Add multi-user support with export feature

- New users table (migration 004) with user_id on exercises, training_sets, sessions - User CRUD endpoints (GET/POST /api/v1/users, DELETE /api/v1/users/{id}) - All existing endpoints scoped to X-User-ID header - CSV export endpoint (GET /api/v1/export) for completed sessions - UserGate in PageShell: blocks app until a user is selected - Settings page for managing users (create, switch, delete) - BottomNav/Sidebar updated with settings navigation - Fix: nil pointer panic in handleDeleteUser on success path - Fix: export download now uses fetch with X-User-ID header instead of window.location.href Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
2026-03-21 23:55:51 +01:00
parent bff85908c3
commit a954f2c59d
24 changed files with 793 additions and 95 deletions
--- a/backend/internal/handler/exercise.go
+++ b/backend/internal/handler/exercise.go
@@ -7,10 +7,15 @@ import (
 )

 func (h *Handler) handleListExercises(w http.ResponseWriter, r *http.Request) {
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
 	muscleGroup := r.URL.Query().Get("muscle_group")
 	query := r.URL.Query().Get("q")

-	exercises, err := h.store.ListExercises(muscleGroup, query)
+	exercises, err := h.store.ListExercises(uid, muscleGroup, query)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "Fehler beim Laden der Übungen")
 		return
@@ -19,6 +24,12 @@ func (h *Handler) handleListExercises(w http.ResponseWriter, r *http.Request) {
 }

 func (h *Handler) handleCreateExercise(w http.ResponseWriter, r *http.Request) {
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+
 	var req model.CreateExerciseRequest
 	if err := decodeJSON(r, &req); err != nil {
 		writeError(w, http.StatusBadRequest, "Ungültiger Request-Body")
@@ -29,7 +40,7 @@ func (h *Handler) handleCreateExercise(w http.ResponseWriter, r *http.Request) {
 		return
 	}

-	exercise, err := h.store.CreateExercise(&req)
+	exercise, err := h.store.CreateExercise(uid, &req)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "Fehler beim Erstellen der Übung")
 		return
@@ -38,6 +49,11 @@ func (h *Handler) handleCreateExercise(w http.ResponseWriter, r *http.Request) {
 }

 func (h *Handler) handleUpdateExercise(w http.ResponseWriter, r *http.Request) {
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
 	id, err := pathID(r, "id")
 	if err != nil {
 		writeError(w, http.StatusBadRequest, "Ungültige ID")
@@ -54,7 +70,7 @@ func (h *Handler) handleUpdateExercise(w http.ResponseWriter, r *http.Request) {
 		return
 	}

-	exercise, err := h.store.UpdateExercise(id, &req)
+	exercise, err := h.store.UpdateExercise(id, uid, &req)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "Fehler beim Aktualisieren der Übung")
 		return
@@ -67,13 +83,18 @@ func (h *Handler) handleUpdateExercise(w http.ResponseWriter, r *http.Request) {
 }

 func (h *Handler) handleDeleteExercise(w http.ResponseWriter, r *http.Request) {
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
 	id, err := pathID(r, "id")
 	if err != nil {
 		writeError(w, http.StatusBadRequest, "Ungültige ID")
 		return
 	}

-	err = h.store.SoftDeleteExercise(id)
+	err = h.store.SoftDeleteExercise(id, uid)
 	if err == sql.ErrNoRows {
 		writeError(w, http.StatusNotFound, "Übung nicht gefunden")
 		return
--- a/backend/internal/handler/export.go
+++ b/backend/internal/handler/export.go
@@ -0,0 +1,42 @@
+package handler
+
+import (
+	"encoding/csv"
+	"net/http"
+	"strconv"
+	"time"
+)
+
+// handleExport gibt alle Trainingsdaten eines Nutzers als CSV zurück.
+func (h *Handler) handleExport(w http.ResponseWriter, r *http.Request) {
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+
+	rows, err := h.store.ExportLogs(uid)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "Export fehlgeschlagen")
+		return
+	}
+
+	filename := "training-export-" + time.Now().Format("2006-01-02") + ".csv"
+	w.Header().Set("Content-Type", "text/csv; charset=utf-8")
+	w.Header().Set("Content-Disposition", "attachment; filename=\""+filename+"\"")
+
+	cw := csv.NewWriter(w)
+	cw.Write([]string{"datum", "uebung", "satz", "gewicht_kg", "wiederholungen", "notiz"})
+
+	for _, row := range rows {
+		cw.Write([]string{
+			row.SessionStarted.Format("2006-01-02 15:04"),
+			row.ExerciseName,
+			strconv.Itoa(row.SetNumber),
+			strconv.FormatFloat(row.WeightKg, 'f', 2, 64),
+			strconv.Itoa(row.Reps),
+			row.Note,
+		})
+	}
+	cw.Flush()
+}
--- a/backend/internal/handler/handler.go
+++ b/backend/internal/handler/handler.go
@@ -2,6 +2,7 @@ package handler

 import (
 	"encoding/json"
+	"errors"
 	"krafttrainer/internal/store"
 	"net/http"
 	"strconv"
@@ -19,6 +20,11 @@ func New(store *store.Store) *Handler {

 // RegisterRoutes registriert alle API-Routen am ServeMux.
 func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
+	// Users (kein X-User-ID Header nötig)
+	mux.HandleFunc("GET /api/v1/users", h.handleListUsers)
+	mux.HandleFunc("POST /api/v1/users", h.handleCreateUser)
+	mux.HandleFunc("DELETE /api/v1/users/{id}", h.handleDeleteUser)
+
 	// Exercises
 	mux.HandleFunc("GET /api/v1/exercises", h.handleListExercises)
 	mux.HandleFunc("POST /api/v1/exercises", h.handleCreateExercise)
@@ -46,6 +52,9 @@ func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
 	mux.HandleFunc("GET /api/v1/exercises/{id}/last-log", h.handleGetLastLog)
 	mux.HandleFunc("GET /api/v1/exercises/{id}/history", h.handleGetExerciseHistory)
 	mux.HandleFunc("GET /api/v1/stats/overview", h.handleGetStatsOverview)
+
+	// Export
+	mux.HandleFunc("GET /api/v1/export", h.handleExport)
 }

 // --- Hilfsfunktionen ---
@@ -81,3 +90,16 @@ func queryInt(r *http.Request, name string, defaultVal int) int {
 	}
 	return n
 }
+
+// userID liest die X-User-ID aus dem Request-Header.
+func userID(r *http.Request) (int64, error) {
+	v := r.Header.Get("X-User-ID")
+	if v == "" {
+		return 0, errors.New("X-User-ID Header fehlt")
+	}
+	id, err := strconv.ParseInt(v, 10, 64)
+	if err != nil || id <= 0 {
+		return 0, errors.New("ungültige User-ID")
+	}
+	return id, nil
+}
--- a/backend/internal/handler/session.go
+++ b/backend/internal/handler/session.go
@@ -8,6 +8,12 @@ import (
 )

 func (h *Handler) handleCreateSession(w http.ResponseWriter, r *http.Request) {
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+
 	var req model.CreateSessionRequest
 	if err := decodeJSON(r, &req); err != nil {
 		writeError(w, http.StatusBadRequest, "Ungültiger Request-Body")
@@ -18,7 +24,7 @@ func (h *Handler) handleCreateSession(w http.ResponseWriter, r *http.Request) {
 		return
 	}

-	session, err := h.store.CreateSession(req.SetID)
+	session, err := h.store.CreateSession(uid, req.SetID)
 	if err != nil {
 		if strings.Contains(err.Error(), "existiert nicht") {
 			writeError(w, http.StatusBadRequest, err.Error())
@@ -31,10 +37,15 @@ func (h *Handler) handleCreateSession(w http.ResponseWriter, r *http.Request) {
 }

 func (h *Handler) handleListSessions(w http.ResponseWriter, r *http.Request) {
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
 	limit := queryInt(r, "limit", 20)
 	offset := queryInt(r, "offset", 0)

-	sessions, err := h.store.ListSessions(limit, offset)
+	sessions, err := h.store.ListSessions(uid, limit, offset)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "Fehler beim Laden der Sessions")
 		return
@@ -62,6 +73,11 @@ func (h *Handler) handleGetSession(w http.ResponseWriter, r *http.Request) {
 }

 func (h *Handler) handleEndSession(w http.ResponseWriter, r *http.Request) {
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
 	id, err := pathID(r, "id")
 	if err != nil {
 		writeError(w, http.StatusBadRequest, "Ungültige ID")
@@ -71,10 +87,9 @@ func (h *Handler) handleEndSession(w http.ResponseWriter, r *http.Request) {
 	var body struct {
 		Note string `json:"note"`
 	}
-	// Body ist optional
 	decodeJSON(r, &body)

-	session, err := h.store.EndSession(id, body.Note)
+	session, err := h.store.EndSession(id, uid, body.Note)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "Fehler beim Beenden der Session")
 		return
--- a/backend/internal/handler/stats.go
+++ b/backend/internal/handler/stats.go
@@ -3,13 +3,18 @@ package handler
 import "net/http"

 func (h *Handler) handleGetLastLog(w http.ResponseWriter, r *http.Request) {
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
 	id, err := pathID(r, "id")
 	if err != nil {
 		writeError(w, http.StatusBadRequest, "Ungültige ID")
 		return
 	}

-	lastLog, err := h.store.GetLastLog(id)
+	lastLog, err := h.store.GetLastLog(id, uid)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "Fehler beim Laden des letzten Logs")
 		return
@@ -22,6 +27,11 @@ func (h *Handler) handleGetLastLog(w http.ResponseWriter, r *http.Request) {
 }

 func (h *Handler) handleGetExerciseHistory(w http.ResponseWriter, r *http.Request) {
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
 	id, err := pathID(r, "id")
 	if err != nil {
 		writeError(w, http.StatusBadRequest, "Ungültige ID")
@@ -29,7 +39,7 @@ func (h *Handler) handleGetExerciseHistory(w http.ResponseWriter, r *http.Reques
 	}
 	limit := queryInt(r, "limit", 30)

-	logs, err := h.store.GetExerciseHistory(id, limit)
+	logs, err := h.store.GetExerciseHistory(id, uid, limit)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "Fehler beim Laden der Übungshistorie")
 		return
@@ -38,7 +48,13 @@ func (h *Handler) handleGetExerciseHistory(w http.ResponseWriter, r *http.Reques
 }

 func (h *Handler) handleGetStatsOverview(w http.ResponseWriter, r *http.Request) {
-	overview, err := h.store.GetStatsOverview()
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+
+	overview, err := h.store.GetStatsOverview(uid)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "Fehler beim Laden der Statistiken")
 		return
--- a/backend/internal/handler/training_set.go
+++ b/backend/internal/handler/training_set.go
@@ -8,7 +8,13 @@ import (
 )

 func (h *Handler) handleListSets(w http.ResponseWriter, r *http.Request) {
-	sets, err := h.store.ListSets()
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+
+	sets, err := h.store.ListSets(uid)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "Fehler beim Laden der Sets")
 		return
@@ -17,6 +23,12 @@ func (h *Handler) handleListSets(w http.ResponseWriter, r *http.Request) {
 }

 func (h *Handler) handleCreateSet(w http.ResponseWriter, r *http.Request) {
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+
 	var req model.CreateSetRequest
 	if err := decodeJSON(r, &req); err != nil {
 		writeError(w, http.StatusBadRequest, "Ungültiger Request-Body")
@@ -27,7 +39,7 @@ func (h *Handler) handleCreateSet(w http.ResponseWriter, r *http.Request) {
 		return
 	}

-	set, err := h.store.CreateSet(&req)
+	set, err := h.store.CreateSet(uid, &req)
 	if err != nil {
 		if strings.Contains(err.Error(), "existiert nicht") {
 			writeError(w, http.StatusBadRequest, err.Error())
@@ -40,6 +52,11 @@ func (h *Handler) handleCreateSet(w http.ResponseWriter, r *http.Request) {
 }

 func (h *Handler) handleUpdateSet(w http.ResponseWriter, r *http.Request) {
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
 	id, err := pathID(r, "id")
 	if err != nil {
 		writeError(w, http.StatusBadRequest, "Ungültige ID")
@@ -56,7 +73,7 @@ func (h *Handler) handleUpdateSet(w http.ResponseWriter, r *http.Request) {
 		return
 	}

-	set, err := h.store.UpdateSet(id, &req)
+	set, err := h.store.UpdateSet(id, uid, &req)
 	if err != nil {
 		if strings.Contains(err.Error(), "existiert nicht") {
 			writeError(w, http.StatusBadRequest, err.Error())
@@ -73,13 +90,18 @@ func (h *Handler) handleUpdateSet(w http.ResponseWriter, r *http.Request) {
 }

 func (h *Handler) handleDeleteSet(w http.ResponseWriter, r *http.Request) {
+	uid, err := userID(r)
+	if err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
 	id, err := pathID(r, "id")
 	if err != nil {
 		writeError(w, http.StatusBadRequest, "Ungültige ID")
 		return
 	}

-	err = h.store.SoftDeleteSet(id)
+	err = h.store.SoftDeleteSet(id, uid)
 	if err == sql.ErrNoRows {
 		writeError(w, http.StatusNotFound, "Set nicht gefunden")
 		return
--- a/backend/internal/handler/user.go
+++ b/backend/internal/handler/user.go
@@ -0,0 +1,59 @@
+package handler
+
+import (
+	"database/sql"
+	"krafttrainer/internal/model"
+	"net/http"
+	"strings"
+)
+
+func (h *Handler) handleListUsers(w http.ResponseWriter, r *http.Request) {
+	users, err := h.store.ListUsers()
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "Fehler beim Laden der Nutzer")
+		return
+	}
+	writeJSON(w, http.StatusOK, users)
+}
+
+func (h *Handler) handleCreateUser(w http.ResponseWriter, r *http.Request) {
+	var req model.CreateUserRequest
+	if err := decodeJSON(r, &req); err != nil {
+		writeError(w, http.StatusBadRequest, "Ungültiger Request-Body")
+		return
+	}
+	if err := req.Validate(); err != nil {
+		writeError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+
+	user, err := h.store.CreateUser(req.Name)
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "Fehler beim Erstellen des Nutzers")
+		return
+	}
+	writeJSON(w, http.StatusCreated, user)
+}
+
+func (h *Handler) handleDeleteUser(w http.ResponseWriter, r *http.Request) {
+	id, err := pathID(r, "id")
+	if err != nil {
+		writeError(w, http.StatusBadRequest, "Ungültige ID")
+		return
+	}
+
+	err = h.store.DeleteUser(id)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			writeError(w, http.StatusNotFound, "Nutzer nicht gefunden")
+			return
+		}
+		if strings.Contains(err.Error(), "LAST_USER") {
+			writeError(w, http.StatusConflict, "Der letzte Nutzer kann nicht gelöscht werden")
+			return
+		}
+		writeError(w, http.StatusInternalServerError, "Fehler beim Löschen des Nutzers")
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}
--- a/backend/internal/model/user.go
+++ b/backend/internal/model/user.go
@@ -0,0 +1,31 @@
+package model
+
+import (
+	"errors"
+	"strings"
+	"time"
+)
+
+// User repräsentiert einen Nutzer der Applikation.
+type User struct {
+	ID        int64     `json:"id"`
+	Name      string    `json:"name"`
+	CreatedAt time.Time `json:"created_at"`
+}
+
+// CreateUserRequest enthält die Felder zum Anlegen eines Nutzers.
+type CreateUserRequest struct {
+	Name string `json:"name"`
+}
+
+// Validate prüft den Request.
+func (r *CreateUserRequest) Validate() error {
+	r.Name = strings.TrimSpace(r.Name)
+	if len(r.Name) == 0 {
+		return errors.New("Name darf nicht leer sein")
+	}
+	if len(r.Name) > 50 {
+		return errors.New("Name darf maximal 50 Zeichen lang sein")
+	}
+	return nil
+}
--- a/backend/internal/store/exercise_store.go
+++ b/backend/internal/store/exercise_store.go
@@ -6,16 +6,17 @@ import (
 	"krafttrainer/internal/model"
 )

-// ListExercises gibt alle nicht-gelöschten Übungen zurück, optional gefiltert.
-func (s *Store) ListExercises(muscleGroup, query string) ([]model.Exercise, error) {
+// ListExercises gibt alle nicht-gelöschten Übungen eines Nutzers zurück, optional gefiltert.
+func (s *Store) ListExercises(userID int64, muscleGroup, query string) ([]model.Exercise, error) {
 	rows, err := s.db.Query(`
 		SELECT id, name, description, muscle_group, weight_step_kg, created_at, updated_at
 		FROM exercises
 		WHERE deleted_at IS NULL
+		  AND user_id = ?
 		  AND (muscle_group = ? OR ? = '')
 		  AND (name LIKE '%' || ? || '%' OR ? = '')
 		ORDER BY name`,
-		muscleGroup, muscleGroup, query, query,
+		userID, muscleGroup, muscleGroup, query, query,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("Übungen abfragen: %w", err)
@@ -36,7 +37,7 @@ func (s *Store) ListExercises(muscleGroup, query string) ([]model.Exercise, erro
 	return exercises, rows.Err()
 }

-// GetExercise gibt eine einzelne Übung zurück.
+// GetExercise gibt eine einzelne Übung zurück (intern, ohne User-Scope).
 func (s *Store) GetExercise(id int64) (*model.Exercise, error) {
 	var e model.Exercise
 	err := s.db.QueryRow(`
@@ -53,11 +54,11 @@ func (s *Store) GetExercise(id int64) (*model.Exercise, error) {
 }

 // CreateExercise legt eine neue Übung an und gibt sie zurück.
-func (s *Store) CreateExercise(req *model.CreateExerciseRequest) (*model.Exercise, error) {
+func (s *Store) CreateExercise(userID int64, req *model.CreateExerciseRequest) (*model.Exercise, error) {
 	result, err := s.db.Exec(`
-		INSERT INTO exercises (name, description, muscle_group, weight_step_kg)
-		VALUES (?, ?, ?, ?)`,
-		req.Name, req.Description, req.MuscleGroup, *req.WeightStepKg,
+		INSERT INTO exercises (name, description, muscle_group, weight_step_kg, user_id)
+		VALUES (?, ?, ?, ?, ?)`,
+		req.Name, req.Description, req.MuscleGroup, *req.WeightStepKg, userID,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("Übung erstellen: %w", err)
@@ -67,14 +68,14 @@ func (s *Store) CreateExercise(req *model.CreateExerciseRequest) (*model.Exercis
 	return s.GetExercise(id)
 }

-// UpdateExercise aktualisiert eine Übung und gibt sie zurück.
-func (s *Store) UpdateExercise(id int64, req *model.CreateExerciseRequest) (*model.Exercise, error) {
+// UpdateExercise aktualisiert eine Übung eines Nutzers und gibt sie zurück.
+func (s *Store) UpdateExercise(id, userID int64, req *model.CreateExerciseRequest) (*model.Exercise, error) {
 	result, err := s.db.Exec(`
 		UPDATE exercises
 		SET name = ?, description = ?, muscle_group = ?, weight_step_kg = ?,
 		    updated_at = CURRENT_TIMESTAMP
-		WHERE id = ? AND deleted_at IS NULL`,
-		req.Name, req.Description, req.MuscleGroup, *req.WeightStepKg, id,
+		WHERE id = ? AND user_id = ? AND deleted_at IS NULL`,
+		req.Name, req.Description, req.MuscleGroup, *req.WeightStepKg, id, userID,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("Übung aktualisieren: %w", err)
@@ -87,11 +88,11 @@ func (s *Store) UpdateExercise(id int64, req *model.CreateExerciseRequest) (*mod
 	return s.GetExercise(id)
 }

-// SoftDeleteExercise markiert eine Übung als gelöscht.
-func (s *Store) SoftDeleteExercise(id int64) error {
+// SoftDeleteExercise markiert eine Übung eines Nutzers als gelöscht.
+func (s *Store) SoftDeleteExercise(id, userID int64) error {
 	result, err := s.db.Exec(`
 		UPDATE exercises SET deleted_at = CURRENT_TIMESTAMP, updated_at = CURRENT_TIMESTAMP
-		WHERE id = ? AND deleted_at IS NULL`, id,
+		WHERE id = ? AND user_id = ? AND deleted_at IS NULL`, id, userID,
 	)
 	if err != nil {
 		return fmt.Errorf("Übung löschen: %w", err)
--- a/backend/internal/store/export_store.go
+++ b/backend/internal/store/export_store.go
@@ -0,0 +1,40 @@
+package store
+
+import (
+	"fmt"
+	"time"
+)
+
+// ExportRow repräsentiert eine Zeile im Trainingsexport.
+type ExportRow struct {
+	SessionStarted time.Time
+	ExerciseName   string
+	SetNumber      int
+	WeightKg       float64
+	Reps           int
+	Note           string
+}
+
+// ExportLogs gibt alle Logs abgeschlossener Sessions eines Nutzers zurück (für AI-Export).
+func (s *Store) ExportLogs(userID int64) ([]ExportRow, error) {
+	rows, err := s.db.Query(`
+		SELECT s.started_at, sl.exercise_name, sl.set_number, sl.weight_kg, sl.reps, sl.note
+		FROM session_logs sl
+		JOIN sessions s ON s.id = sl.session_id
+		WHERE s.ended_at IS NOT NULL AND s.user_id = ?
+		ORDER BY s.started_at, sl.exercise_name, sl.set_number`, userID)
+	if err != nil {
+		return nil, fmt.Errorf("Export abfragen: %w", err)
+	}
+	defer rows.Close()
+
+	var result []ExportRow
+	for rows.Next() {
+		var row ExportRow
+		if err := rows.Scan(&row.SessionStarted, &row.ExerciseName, &row.SetNumber, &row.WeightKg, &row.Reps, &row.Note); err != nil {
+			return nil, fmt.Errorf("Export scannen: %w", err)
+		}
+		result = append(result, row)
+	}
+	return result, rows.Err()
+}
--- a/backend/internal/store/session_store.go
+++ b/backend/internal/store/session_store.go
@@ -7,11 +7,10 @@ import (
 	"strings"
 )

-// CreateSession startet eine neue Trainingseinheit.
-func (s *Store) CreateSession(setID int64) (*model.Session, error) {
-	// Set prüfen
+// CreateSession startet eine neue Trainingseinheit für einen Nutzer.
+func (s *Store) CreateSession(userID, setID int64) (*model.Session, error) {
 	var setName string
-	err := s.db.QueryRow(`SELECT name FROM training_sets WHERE id = ? AND deleted_at IS NULL`, setID).Scan(&setName)
+	err := s.db.QueryRow(`SELECT name FROM training_sets WHERE id = ? AND user_id = ? AND deleted_at IS NULL`, setID, userID).Scan(&setName)
 	if err == sql.ErrNoRows {
 		return nil, fmt.Errorf("Set %d existiert nicht", setID)
 	}
@@ -19,7 +18,7 @@ func (s *Store) CreateSession(setID int64) (*model.Session, error) {
 		return nil, fmt.Errorf("Set prüfen: %w", err)
 	}

-	result, err := s.db.Exec(`INSERT INTO sessions (set_id) VALUES (?)`, setID)
+	result, err := s.db.Exec(`INSERT INTO sessions (set_id, user_id) VALUES (?, ?)`, setID, userID)
 	if err != nil {
 		return nil, fmt.Errorf("Session erstellen: %w", err)
 	}
@@ -28,7 +27,7 @@ func (s *Store) CreateSession(setID int64) (*model.Session, error) {
 	return s.GetSession(id)
 }

-// GetSession gibt eine Session mit allen Logs zurück.
+// GetSession gibt eine Session mit allen Logs zurück (intern, ohne User-Scope).
 func (s *Store) GetSession(id int64) (*model.Session, error) {
 	var sess model.Session
 	err := s.db.QueryRow(`
@@ -52,11 +51,11 @@ func (s *Store) GetSession(id int64) (*model.Session, error) {
 	return &sess, nil
 }

-// EndSession beendet eine Session.
-func (s *Store) EndSession(id int64, note string) (*model.Session, error) {
+// EndSession beendet eine Session eines Nutzers.
+func (s *Store) EndSession(id, userID int64, note string) (*model.Session, error) {
 	result, err := s.db.Exec(`
 		UPDATE sessions SET ended_at = CURRENT_TIMESTAMP, note = ?
-		WHERE id = ? AND ended_at IS NULL`, note, id,
+		WHERE id = ? AND user_id = ? AND ended_at IS NULL`, note, id, userID,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("Session beenden: %w", err)
@@ -68,14 +67,15 @@ func (s *Store) EndSession(id int64, note string) (*model.Session, error) {
 	return s.GetSession(id)
 }

-// ListSessions gibt paginierte Sessions zurück (neueste zuerst).
-func (s *Store) ListSessions(limit, offset int) ([]model.Session, error) {
+// ListSessions gibt paginierte Sessions eines Nutzers zurück (neueste zuerst).
+func (s *Store) ListSessions(userID int64, limit, offset int) ([]model.Session, error) {
 	rows, err := s.db.Query(`
 		SELECT s.id, s.set_id, ts.name, s.started_at, s.ended_at, s.note
 		FROM sessions s
 		JOIN training_sets ts ON ts.id = s.set_id
+		WHERE s.user_id = ?
 		ORDER BY s.started_at DESC
-		LIMIT ? OFFSET ?`, limit, offset,
+		LIMIT ? OFFSET ?`, userID, limit, offset,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("Sessions abfragen: %w", err)
@@ -98,12 +98,10 @@ func (s *Store) ListSessions(limit, offset int) ([]model.Session, error) {

 // CreateLog fügt einen Satz zu einer offenen Session hinzu.
 func (s *Store) CreateLog(sessionID int64, req *model.CreateLogRequest) (*model.SessionLog, error) {
-	// Session offen?
 	if err := s.checkSessionOpen(sessionID); err != nil {
 		return nil, err
 	}

-	// Übungsname denormalisiert speichern
 	var exerciseName string
 	err := s.db.QueryRow(`SELECT name FROM exercises WHERE id = ? AND deleted_at IS NULL`, req.ExerciseID).Scan(&exerciseName)
 	if err == sql.ErrNoRows {
@@ -135,7 +133,6 @@ func (s *Store) UpdateLog(sessionID, logID int64, req *model.UpdateLogRequest) (
 		return nil, err
 	}

-	// Log gehört zur Session?
 	var exists bool
 	err := s.db.QueryRow(`SELECT EXISTS(SELECT 1 FROM session_logs WHERE id = ? AND session_id = ?)`, logID, sessionID).Scan(&exists)
 	if err != nil {
@@ -145,7 +142,6 @@ func (s *Store) UpdateLog(sessionID, logID int64, req *model.UpdateLogRequest) (
 		return nil, nil
 	}

-	// Partielle Updates
 	updates := []string{}
 	args := []any{}
 	if req.WeightKg != nil {
@@ -192,13 +188,15 @@ func (s *Store) DeleteLog(sessionID, logID int64) error {
 	return nil
 }

-// GetLastLog gibt die letzten Werte einer Übung zurück.
-func (s *Store) GetLastLog(exerciseID int64) (*model.LastLogResponse, error) {
+// GetLastLog gibt die letzten Werte einer Übung für einen Nutzer zurück.
+func (s *Store) GetLastLog(exerciseID, userID int64) (*model.LastLogResponse, error) {
 	var resp model.LastLogResponse
 	err := s.db.QueryRow(`
-		SELECT weight_kg, reps FROM session_logs
-		WHERE exercise_id = ?
-		ORDER BY logged_at DESC LIMIT 1`, exerciseID,
+		SELECT sl.weight_kg, sl.reps
+		FROM session_logs sl
+		JOIN sessions s ON s.id = sl.session_id
+		WHERE sl.exercise_id = ? AND s.user_id = ?
+		ORDER BY sl.logged_at DESC LIMIT 1`, exerciseID, userID,
 	).Scan(&resp.WeightKg, &resp.Reps)
 	if err == sql.ErrNoRows {
 		return nil, nil
--- a/backend/internal/store/set_store.go
+++ b/backend/internal/store/set_store.go
@@ -6,11 +6,11 @@ import (
 	"krafttrainer/internal/model"
 )

-// ListSets gibt alle nicht-gelöschten Sets mit ihren Übungen zurück.
-func (s *Store) ListSets() ([]model.TrainingSet, error) {
+// ListSets gibt alle nicht-gelöschten Sets eines Nutzers mit ihren Übungen zurück.
+func (s *Store) ListSets(userID int64) ([]model.TrainingSet, error) {
 	rows, err := s.db.Query(`
 		SELECT id, name, created_at FROM training_sets
-		WHERE deleted_at IS NULL ORDER BY name`)
+		WHERE deleted_at IS NULL AND user_id = ? ORDER BY name`, userID)
 	if err != nil {
 		return nil, fmt.Errorf("Sets abfragen: %w", err)
 	}
@@ -41,7 +41,7 @@ func (s *Store) ListSets() ([]model.TrainingSet, error) {
 	return sets, nil
 }

-// GetSet gibt ein einzelnes Set mit Übungen zurück.
+// GetSet gibt ein einzelnes Set mit Übungen zurück (intern, ohne User-Scope).
 func (s *Store) GetSet(id int64) (*model.TrainingSet, error) {
 	var ts model.TrainingSet
 	err := s.db.QueryRow(`
@@ -63,17 +63,16 @@ func (s *Store) GetSet(id int64) (*model.TrainingSet, error) {
 }

 // CreateSet legt ein neues Set an (in einer Transaktion).
-func (s *Store) CreateSet(req *model.CreateSetRequest) (*model.TrainingSet, error) {
+func (s *Store) CreateSet(userID int64, req *model.CreateSetRequest) (*model.TrainingSet, error) {
 	tx, err := s.db.Begin()
 	if err != nil {
 		return nil, fmt.Errorf("Transaktion starten: %w", err)
 	}
 	defer tx.Rollback()

-	// Prüfen ob alle Übungen existieren
 	for _, eid := range req.ExerciseIDs {
 		var exists bool
-		err := tx.QueryRow(`SELECT EXISTS(SELECT 1 FROM exercises WHERE id = ? AND deleted_at IS NULL)`, eid).Scan(&exists)
+		err := tx.QueryRow(`SELECT EXISTS(SELECT 1 FROM exercises WHERE id = ? AND user_id = ? AND deleted_at IS NULL)`, eid, userID).Scan(&exists)
 		if err != nil {
 			return nil, fmt.Errorf("Übung prüfen: %w", err)
 		}
@@ -82,7 +81,7 @@ func (s *Store) CreateSet(req *model.CreateSetRequest) (*model.TrainingSet, erro
 		}
 	}

-	result, err := tx.Exec(`INSERT INTO training_sets (name) VALUES (?)`, req.Name)
+	result, err := tx.Exec(`INSERT INTO training_sets (name, user_id) VALUES (?, ?)`, req.Name, userID)
 	if err != nil {
 		return nil, fmt.Errorf("Set erstellen: %w", err)
 	}
@@ -102,17 +101,16 @@ func (s *Store) CreateSet(req *model.CreateSetRequest) (*model.TrainingSet, erro
 	return s.GetSet(id)
 }

-// UpdateSet aktualisiert ein Set (Name + Übungszuordnungen).
-func (s *Store) UpdateSet(id int64, req *model.UpdateSetRequest) (*model.TrainingSet, error) {
+// UpdateSet aktualisiert ein Set eines Nutzers (Name + Übungszuordnungen).
+func (s *Store) UpdateSet(id, userID int64, req *model.UpdateSetRequest) (*model.TrainingSet, error) {
 	tx, err := s.db.Begin()
 	if err != nil {
 		return nil, fmt.Errorf("Transaktion starten: %w", err)
 	}
 	defer tx.Rollback()

-	// Prüfen ob Set existiert
 	var exists bool
-	err = tx.QueryRow(`SELECT EXISTS(SELECT 1 FROM training_sets WHERE id = ? AND deleted_at IS NULL)`, id).Scan(&exists)
+	err = tx.QueryRow(`SELECT EXISTS(SELECT 1 FROM training_sets WHERE id = ? AND user_id = ? AND deleted_at IS NULL)`, id, userID).Scan(&exists)
 	if err != nil {
 		return nil, fmt.Errorf("Set prüfen: %w", err)
 	}
@@ -120,10 +118,9 @@ func (s *Store) UpdateSet(id int64, req *model.UpdateSetRequest) (*model.Trainin
 		return nil, nil
 	}

-	// Prüfen ob alle Übungen existieren
 	for _, eid := range req.ExerciseIDs {
 		var eExists bool
-		err := tx.QueryRow(`SELECT EXISTS(SELECT 1 FROM exercises WHERE id = ? AND deleted_at IS NULL)`, eid).Scan(&eExists)
+		err := tx.QueryRow(`SELECT EXISTS(SELECT 1 FROM exercises WHERE id = ? AND user_id = ? AND deleted_at IS NULL)`, eid, userID).Scan(&eExists)
 		if err != nil {
 			return nil, fmt.Errorf("Übung prüfen: %w", err)
 		}
@@ -155,11 +152,11 @@ func (s *Store) UpdateSet(id int64, req *model.UpdateSetRequest) (*model.Trainin
 	return s.GetSet(id)
 }

-// SoftDeleteSet markiert ein Set als gelöscht.
-func (s *Store) SoftDeleteSet(id int64) error {
+// SoftDeleteSet markiert ein Set eines Nutzers als gelöscht.
+func (s *Store) SoftDeleteSet(id, userID int64) error {
 	result, err := s.db.Exec(`
 		UPDATE training_sets SET deleted_at = CURRENT_TIMESTAMP, updated_at = CURRENT_TIMESTAMP
-		WHERE id = ? AND deleted_at IS NULL`, id,
+		WHERE id = ? AND user_id = ? AND deleted_at IS NULL`, id, userID,
 	)
 	if err != nil {
 		return fmt.Errorf("Set löschen: %w", err)
--- a/backend/internal/store/stats_store.go
+++ b/backend/internal/store/stats_store.go
@@ -13,16 +13,16 @@ type StatsOverview struct {
 	Exercises        []model.ExerciseStats `json:"exercises"`
 }

-// GetStatsOverview gibt die Gesamtstatistik zurück.
-func (s *Store) GetStatsOverview() (*StatsOverview, error) {
+// GetStatsOverview gibt die Gesamtstatistik eines Nutzers zurück.
+func (s *Store) GetStatsOverview(userID int64) (*StatsOverview, error) {
 	var overview StatsOverview

 	err := s.db.QueryRow(`
 		SELECT
-			(SELECT COUNT(*) FROM sessions WHERE ended_at IS NOT NULL),
-			(SELECT COALESCE(SUM(weight_kg * reps), 0) FROM session_logs),
-			(SELECT COUNT(*) FROM sessions WHERE ended_at IS NOT NULL AND started_at >= date('now', '-7 days'))
-	`).Scan(&overview.TotalSessions, &overview.TotalVolumeKg, &overview.SessionsThisWeek)
+			(SELECT COUNT(*) FROM sessions WHERE user_id = ? AND ended_at IS NOT NULL),
+			(SELECT COALESCE(SUM(sl.weight_kg * sl.reps), 0) FROM session_logs sl JOIN sessions s ON s.id = sl.session_id WHERE s.user_id = ?),
+			(SELECT COUNT(*) FROM sessions WHERE user_id = ? AND ended_at IS NOT NULL AND started_at >= date('now', '-7 days'))
+	`, userID, userID, userID).Scan(&overview.TotalSessions, &overview.TotalVolumeKg, &overview.SessionsThisWeek)
 	if err != nil {
 		return nil, fmt.Errorf("Übersicht abfragen: %w", err)
 	}
@@ -36,8 +36,10 @@ func (s *Store) GetStatsOverview() (*StatsOverview, error) {
 			COUNT(*) as total_sets,
 			MAX(sl.logged_at) as last_trained
 		FROM session_logs sl
+		JOIN sessions s ON s.id = sl.session_id
+		WHERE s.user_id = ?
 		GROUP BY sl.exercise_id
-		ORDER BY last_trained DESC`)
+		ORDER BY last_trained DESC`, userID)
 	if err != nil {
 		return nil, fmt.Errorf("Übungs-Stats abfragen: %w", err)
 	}
@@ -56,14 +58,15 @@ func (s *Store) GetStatsOverview() (*StatsOverview, error) {
 	return &overview, rows.Err()
 }

-// GetExerciseHistory gibt die letzten N Logs einer Übung zurück.
-func (s *Store) GetExerciseHistory(exerciseID int64, limit int) ([]model.SessionLog, error) {
+// GetExerciseHistory gibt die letzten N Logs einer Übung für einen Nutzer zurück.
+func (s *Store) GetExerciseHistory(exerciseID, userID int64, limit int) ([]model.SessionLog, error) {
 	rows, err := s.db.Query(`
-		SELECT id, session_id, exercise_id, exercise_name, set_number, weight_kg, reps, note, logged_at
-		FROM session_logs
-		WHERE exercise_id = ?
-		ORDER BY logged_at DESC
-		LIMIT ?`, exerciseID, limit,
+		SELECT sl.id, sl.session_id, sl.exercise_id, sl.exercise_name, sl.set_number, sl.weight_kg, sl.reps, sl.note, sl.logged_at
+		FROM session_logs sl
+		JOIN sessions s ON s.id = sl.session_id
+		WHERE sl.exercise_id = ? AND s.user_id = ?
+		ORDER BY sl.logged_at DESC
+		LIMIT ?`, exerciseID, userID, limit,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("Übungshistorie abfragen: %w", err)
--- a/backend/internal/store/user_store.go
+++ b/backend/internal/store/user_store.go
@@ -0,0 +1,73 @@
+package store
+
+import (
+	"database/sql"
+	"fmt"
+	"krafttrainer/internal/model"
+)
+
+// ListUsers gibt alle Nutzer zurück.
+func (s *Store) ListUsers() ([]model.User, error) {
+	rows, err := s.db.Query(`SELECT id, name, created_at FROM users ORDER BY created_at`)
+	if err != nil {
+		return nil, fmt.Errorf("Nutzer abfragen: %w", err)
+	}
+	defer rows.Close()
+
+	var users []model.User
+	for rows.Next() {
+		var u model.User
+		if err := rows.Scan(&u.ID, &u.Name, &u.CreatedAt); err != nil {
+			return nil, fmt.Errorf("Nutzer scannen: %w", err)
+		}
+		users = append(users, u)
+	}
+	if users == nil {
+		users = []model.User{}
+	}
+	return users, rows.Err()
+}
+
+// CreateUser legt einen neuen Nutzer an.
+func (s *Store) CreateUser(name string) (*model.User, error) {
+	result, err := s.db.Exec(`INSERT INTO users (name) VALUES (?)`, name)
+	if err != nil {
+		return nil, fmt.Errorf("Nutzer erstellen: %w", err)
+	}
+	id, _ := result.LastInsertId()
+	return s.getUser(id)
+}
+
+// DeleteUser löscht einen Nutzer, sofern noch mindestens ein weiterer existiert.
+func (s *Store) DeleteUser(id int64) error {
+	var count int
+	if err := s.db.QueryRow(`SELECT COUNT(*) FROM users`).Scan(&count); err != nil {
+		return fmt.Errorf("Nutzeranzahl prüfen: %w", err)
+	}
+	if count <= 1 {
+		return fmt.Errorf("LAST_USER: letzter Nutzer kann nicht gelöscht werden")
+	}
+
+	result, err := s.db.Exec(`DELETE FROM users WHERE id = ?`, id)
+	if err != nil {
+		return fmt.Errorf("Nutzer löschen: %w", err)
+	}
+	rows, _ := result.RowsAffected()
+	if rows == 0 {
+		return sql.ErrNoRows
+	}
+	return nil
+}
+
+func (s *Store) getUser(id int64) (*model.User, error) {
+	var u model.User
+	err := s.db.QueryRow(`SELECT id, name, created_at FROM users WHERE id = ?`, id).
+		Scan(&u.ID, &u.Name, &u.CreatedAt)
+	if err == sql.ErrNoRows {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, fmt.Errorf("Nutzer abfragen: %w", err)
+	}
+	return &u, nil
+}
--- a/backend/migrations/004_add_users.down.sql
+++ b/backend/migrations/004_add_users.down.sql
@@ -0,0 +1,4 @@
+ALTER TABLE sessions      DROP COLUMN user_id;
+ALTER TABLE training_sets DROP COLUMN user_id;
+ALTER TABLE exercises     DROP COLUMN user_id;
+DROP TABLE IF EXISTS users;
--- a/backend/migrations/004_add_users.up.sql
+++ b/backend/migrations/004_add_users.up.sql
@@ -0,0 +1,12 @@
+CREATE TABLE users (
+    id         INTEGER PRIMARY KEY AUTOINCREMENT,
+    name       TEXT NOT NULL CHECK(length(name) >= 1 AND length(name) <= 50),
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Standardnutzer für bestehende Daten
+INSERT INTO users (name) VALUES ('Standard');
+
+ALTER TABLE exercises     ADD COLUMN user_id INTEGER NOT NULL DEFAULT 1;
+ALTER TABLE training_sets ADD COLUMN user_id INTEGER NOT NULL DEFAULT 1;
+ALTER TABLE sessions      ADD COLUMN user_id INTEGER NOT NULL DEFAULT 1;
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -4,6 +4,7 @@ import { ExercisesPage } from './pages/ExercisesPage';
 import { SetsPage } from './pages/SetsPage';
 import { TrainingPage } from './pages/TrainingPage';
 import { HistoryPage } from './pages/HistoryPage';
+import { SettingsPage } from './pages/SettingsPage';

 const router = createBrowserRouter([
  {
@@ -13,6 +14,7 @@ const router = createBrowserRouter([
      { path: '/sets', element: <SetsPage /> },
      { path: '/training', element: <TrainingPage /> },
      { path: '/history', element: <HistoryPage /> },
+      { path: '/settings', element: <SettingsPage /> },
    ],
  },
 ]);
--- a/frontend/src/api/client.ts
+++ b/frontend/src/api/client.ts
@@ -5,6 +5,7 @@ import type {
  SessionLog,
  LastLogResponse,
  ExerciseStats,
+  User,
  CreateExerciseRequest,
  CreateSetRequest,
  UpdateSetRequest,
@@ -12,6 +13,7 @@ import type {
  CreateLogRequest,
  UpdateLogRequest,
 } from '../types';
+import { getActiveUserId } from '../stores/userStore';

 export class ApiError extends Error {
  constructor(
@@ -27,8 +29,12 @@ async function request<T>(
  url: string,
  options?: RequestInit,
 ): Promise<T> {
+  const headers: Record<string, string> = { 'Content-Type': 'application/json' };
+  const uid = getActiveUserId();
+  if (uid) headers['X-User-ID'] = uid;
+
  const res = await fetch(url, {
-    headers: { 'Content-Type': 'application/json' },
+    headers,
    ...options,
  });

@@ -46,6 +52,21 @@ async function request<T>(
 }

 export const api = {
+  users: {
+    list(): Promise<User[]> {
+      return request<User[]>('/api/v1/users');
+    },
+    create(name: string): Promise<User> {
+      return request<User>('/api/v1/users', {
+        method: 'POST',
+        body: JSON.stringify({ name }),
+      });
+    },
+    delete(id: number): Promise<void> {
+      return request<void>(`/api/v1/users/${id}`, { method: 'DELETE' });
+    },
+  },
+
  exercises: {
    list(muscleGroup?: string, q?: string): Promise<Exercise[]> {
      const params = new URLSearchParams();
--- a/frontend/src/components/layout/BottomNav.tsx
+++ b/frontend/src/components/layout/BottomNav.tsx
@@ -1,4 +1,5 @@
 import { NavLink } from 'react-router-dom';
+import { useUserStore } from '../../stores/userStore';

 const navItems = [
  {
@@ -37,6 +38,16 @@ const navItems = [
      </svg>
    ),
  },
+  {
+    to: '/settings',
+    label: 'Einstellungen',
+    icon: (
+      <svg className="w-6 h-6" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>
+        <path strokeLinecap="round" strokeLinejoin="round" d="M10.325 4.317c.426-1.756 2.924-1.756 3.35 0a1.724 1.724 0 002.573 1.066c1.543-.94 3.31.826 2.37 2.37a1.724 1.724 0 001.065 2.572c1.756.426 1.756 2.924 0 3.35a1.724 1.724 0 00-1.066 2.573c.94 1.543-.826 3.31-2.37 2.37a1.724 1.724 0 00-2.572 1.065c-.426 1.756-2.924 1.756-3.35 0a1.724 1.724 0 00-2.573-1.066c-1.543.94-3.31-.826-2.37-2.37a1.724 1.724 0 00-1.065-2.572c-1.756-.426-1.756-2.924 0-3.35a1.724 1.724 0 001.066-2.573c-.94-1.543.826-3.31 2.37-2.37.996.608 2.296.07 2.572-1.065z" />
+        <path strokeLinecap="round" strokeLinejoin="round" d="M15 12a3 3 0 11-6 0 3 3 0 016 0z" />
+      </svg>
+    ),
+  },
 ];

 export function BottomNav() {
@@ -64,10 +75,12 @@ export function BottomNav() {
 }

 export function Sidebar() {
+  const { activeUser } = useUserStore();
+
  return (
    <nav className="hidden md:flex flex-col w-56 bg-gray-900 border-r border-gray-800 min-h-screen p-4">
      <h1 className="text-xl font-bold text-blue-500 mb-8">Krafttrainer</h1>
-      <div className="flex flex-col gap-1">
+      <div className="flex flex-col gap-1 flex-1">
        {navItems.map((item) => (
          <NavLink
            key={item.to}
@@ -86,6 +99,14 @@ export function Sidebar() {
          </NavLink>
        ))}
      </div>
+      {activeUser && (
+        <div className="pt-4 border-t border-gray-800 flex items-center gap-2">
+          <div className="w-7 h-7 rounded-full bg-blue-600 flex items-center justify-center text-white text-xs font-bold flex-shrink-0">
+            {activeUser.name.charAt(0).toUpperCase()}
+          </div>
+          <span className="text-sm text-gray-300 truncate">{activeUser.name}</span>
+        </div>
+      )}
    </nav>
  );
 }
--- a/frontend/src/components/layout/PageShell.tsx
+++ b/frontend/src/components/layout/PageShell.tsx
@@ -1,9 +1,98 @@
+import { useEffect, useState } from 'react';
 import { Outlet } from 'react-router-dom';
 import { BottomNav, Sidebar } from './BottomNav';
 import { ToastContainer } from './Toast';
+import { useUserStore } from '../../stores/userStore';
+
+function UserGate({ children }: { children: React.ReactNode }) {
+  const { users, activeUser, setActiveUser, fetchUsers, createUser } = useUserStore();
+  const [newName, setNewName] = useState('');
+  const [loading, setLoading] = useState(false);
+  const [fetched, setFetched] = useState(false);
+
+  useEffect(() => {
+    fetchUsers().then(() => setFetched(true));
+  }, [fetchUsers]);
+
+  if (!fetched) {
+    return (
+      <div className="min-h-screen bg-gray-950 flex items-center justify-center">
+        <div className="text-gray-400">Laden…</div>
+      </div>
+    );
+  }
+
+  if (!activeUser) {
+    async function handleCreate(e: React.FormEvent) {
+      e.preventDefault();
+      const name = newName.trim();
+      if (!name) return;
+      setLoading(true);
+      const user = await createUser(name);
+      setLoading(false);
+      if (user) setActiveUser(user);
+    }
+
+    return (
+      <div className="min-h-screen bg-gray-950 flex items-center justify-center px-4">
+        <div className="w-full max-w-sm space-y-6">
+          <div className="text-center">
+            <h1 className="text-3xl font-bold text-blue-500 mb-1">Krafttrainer</h1>
+            <p className="text-gray-400">Wer trainiert heute?</p>
+          </div>
+
+          {users.length > 0 && (
+            <ul className="space-y-2">
+              {users.map((user) => (
+                <li key={user.id}>
+                  <button
+                    onClick={() => setActiveUser(user)}
+                    className="w-full flex items-center gap-3 bg-gray-900 hover:bg-gray-800 rounded-lg px-4 py-3 min-h-[56px] transition-colors text-left"
+                  >
+                    <div className="w-9 h-9 rounded-full bg-blue-600 flex items-center justify-center text-white font-bold text-sm flex-shrink-0">
+                      {user.name.charAt(0).toUpperCase()}
+                    </div>
+                    <span className="text-gray-100 font-medium">{user.name}</span>
+                  </button>
+                </li>
+              ))}
+            </ul>
+          )}
+
+          <form onSubmit={handleCreate} className="space-y-3">
+            <p className="text-sm text-gray-400">
+              {users.length === 0 ? 'Ersten Nutzer anlegen:' : 'Oder neuen Nutzer anlegen:'}
+            </p>
+            <div className="flex gap-2">
+              <input
+                type="text"
+                value={newName}
+                onChange={(e) => setNewName(e.target.value)}
+                placeholder="Name"
+                maxLength={50}
+                autoFocus
+                className="flex-1 bg-gray-900 border border-gray-700 rounded-lg px-3 py-2 text-gray-100 placeholder-gray-500 focus:outline-none focus:border-blue-500 min-h-[44px]"
+              />
+              <button
+                type="submit"
+                disabled={loading || !newName.trim()}
+                className="px-4 py-2 bg-blue-600 hover:bg-blue-500 disabled:opacity-50 text-white rounded-lg font-medium min-h-[44px] transition-colors"
+              >
+                Los
+              </button>
+            </div>
+          </form>
+        </div>
+      </div>
+    );
+  }
+
+  return <>{children}</>;
+}

 export function PageShell() {
  return (
+    <UserGate>
      <div className="flex min-h-screen">
        <Sidebar />
        <main className="flex-1 pb-20 md:pb-0">
@@ -14,5 +103,6 @@ export function PageShell() {
        <BottomNav />
        <ToastContainer />
      </div>
+    </UserGate>
  );
 }
--- a/frontend/src/pages/HistoryPage.tsx
+++ b/frontend/src/pages/HistoryPage.tsx
@@ -1,15 +1,47 @@
 import { useState } from 'react';
 import { SessionList } from '../components/history/SessionList';
 import { ExerciseChart } from '../components/history/ExerciseChart';
+import { getActiveUserId } from '../stores/userStore';

 type Tab = 'history' | 'stats';

+async function downloadExport() {
+  const uid = getActiveUserId();
+  const headers: Record<string, string> = {};
+  if (uid) headers['X-User-ID'] = uid;
+
+  const res = await fetch('/api/v1/export', { headers });
+  if (!res.ok) return;
+
+  const blob = await res.blob();
+  const url = URL.createObjectURL(blob);
+  const a = document.createElement('a');
+  a.href = url;
+  a.download = `training-export-${new Date().toISOString().slice(0, 10)}.csv`;
+  document.body.appendChild(a);
+  a.click();
+  document.body.removeChild(a);
+  URL.revokeObjectURL(url);
+}
+
 export function HistoryPage() {
  const [activeTab, setActiveTab] = useState<Tab>('history');

  return (
    <div className="space-y-4">
+      <div className="flex items-center justify-between">
        <h1 className="text-2xl font-bold text-gray-100">Historie</h1>
+        <button
+          onClick={downloadExport}
+          className="flex items-center gap-2 px-3 py-2 rounded-lg bg-gray-800 text-gray-300 hover:text-white hover:bg-gray-700 text-sm min-h-[44px] transition-colors"
+          title="Trainingsdaten als CSV exportieren"
+        >
+          <svg xmlns="http://www.w3.org/2000/svg" className="w-4 h-4" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+            <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M4 16v1a3 3 0 003 3h10a3 3 0 003-3v-1m-4-4l-4 4m0 0l-4-4m4 4V4" />
+          </svg>
+          Export CSV
+        </button>
+      </div>

      {/* Tab Toggle */}
      <div className="flex bg-gray-900 rounded-lg p-1">
--- a/frontend/src/pages/SettingsPage.tsx
+++ b/frontend/src/pages/SettingsPage.tsx
@@ -0,0 +1,95 @@
+import { useEffect, useState } from 'react';
+import { useUserStore } from '../stores/userStore';
+
+export function SettingsPage() {
+  const { users, activeUser, setActiveUser, fetchUsers, createUser, deleteUser } =
+    useUserStore();
+  const [newName, setNewName] = useState('');
+  const [loading, setLoading] = useState(false);
+
+  useEffect(() => {
+    fetchUsers();
+  }, [fetchUsers]);
+
+  async function handleCreate(e: React.FormEvent) {
+    e.preventDefault();
+    const name = newName.trim();
+    if (!name) return;
+    setLoading(true);
+    const user = await createUser(name);
+    setLoading(false);
+    if (user) setNewName('');
+  }
+
+  async function handleDelete(id: number) {
+    await deleteUser(id);
+  }
+
+  return (
+    <div className="space-y-6">
+      <h1 className="text-2xl font-bold text-gray-100">Einstellungen</h1>
+
+      <section className="space-y-3">
+        <h2 className="text-lg font-semibold text-gray-200">Nutzer</h2>
+
+        <ul className="space-y-2">
+          {users.map((user) => (
+            <li
+              key={user.id}
+              className="flex items-center justify-between bg-gray-900 rounded-lg px-4 py-3"
+            >
+              <button
+                onClick={() => setActiveUser(user)}
+                className="flex items-center gap-3 flex-1 text-left"
+              >
+                <div
+                  className={`w-8 h-8 rounded-full flex items-center justify-center text-sm font-bold ${
+                    activeUser?.id === user.id
+                      ? 'bg-blue-600 text-white'
+                      : 'bg-gray-700 text-gray-300'
+                  }`}
+                >
+                  {user.name.charAt(0).toUpperCase()}
+                </div>
+                <span className="text-gray-100">{user.name}</span>
+                {activeUser?.id === user.id && (
+                  <span className="text-xs text-blue-400 font-medium">Aktiv</span>
+                )}
+              </button>
+
+              {users.length > 1 && (
+                <button
+                  onClick={() => handleDelete(user.id)}
+                  className="p-2 text-gray-500 hover:text-red-400 transition-colors min-h-[44px] min-w-[44px] flex items-center justify-center"
+                  title="Nutzer löschen"
+                >
+                  <svg xmlns="http://www.w3.org/2000/svg" className="w-4 h-4" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+                    <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M19 7l-.867 12.142A2 2 0 0116.138 21H7.862a2 2 0 01-1.995-1.858L5 7m5 4v6m4-6v6m1-10V4a1 1 0 00-1-1h-4a1 1 0 00-1 1v3M4 7h16" />
+                  </svg>
+                </button>
+              )}
+            </li>
+          ))}
+        </ul>
+
+        <form onSubmit={handleCreate} className="flex gap-2">
+          <input
+            type="text"
+            value={newName}
+            onChange={(e) => setNewName(e.target.value)}
+            placeholder="Neuer Nutzername"
+            maxLength={50}
+            className="flex-1 bg-gray-900 border border-gray-700 rounded-lg px-3 py-2 text-gray-100 placeholder-gray-500 focus:outline-none focus:border-blue-500 min-h-[44px]"
+          />
+          <button
+            type="submit"
+            disabled={loading || !newName.trim()}
+            className="px-4 py-2 bg-blue-600 hover:bg-blue-500 disabled:opacity-50 text-white rounded-lg font-medium min-h-[44px] transition-colors"
+          >
+            Hinzufügen
+          </button>
+        </form>
+      </section>
+    </div>
+  );
+}
--- a/frontend/src/stores/userStore.ts
+++ b/frontend/src/stores/userStore.ts
@@ -0,0 +1,71 @@
+import { create } from 'zustand';
+import { persist } from 'zustand/middleware';
+import type { User } from '../types';
+
+interface UserState {
+  users: User[];
+  activeUser: User | null;
+  setActiveUser: (user: User) => void;
+  fetchUsers: () => Promise<void>;
+  createUser: (name: string) => Promise<User | null>;
+  deleteUser: (id: number) => Promise<boolean>;
+}
+
+export const useUserStore = create<UserState>()(
+  persist(
+    (set, get) => ({
+      users: [],
+      activeUser: null,
+
+      setActiveUser: (user) => set({ activeUser: user }),
+
+      fetchUsers: async () => {
+        const res = await fetch('/api/v1/users', {
+          headers: { 'Content-Type': 'application/json' },
+        });
+        if (!res.ok) return;
+        const users: User[] = await res.json();
+        set({ users });
+
+        // Aktiven Nutzer aktualisieren falls er sich geändert hat
+        const { activeUser } = get();
+        if (activeUser) {
+          const updated = users.find((u) => u.id === activeUser.id);
+          if (updated) set({ activeUser: updated });
+        }
+      },
+
+      createUser: async (name) => {
+        const res = await fetch('/api/v1/users', {
+          method: 'POST',
+          headers: { 'Content-Type': 'application/json' },
+          body: JSON.stringify({ name }),
+        });
+        if (!res.ok) return null;
+        const user: User = await res.json();
+        set((s) => ({ users: [...s.users, user] }));
+        return user;
+      },
+
+      deleteUser: async (id) => {
+        const res = await fetch(`/api/v1/users/${id}`, { method: 'DELETE' });
+        if (!res.ok) return false;
+        set((s) => ({
+          users: s.users.filter((u) => u.id !== id),
+          activeUser: s.activeUser?.id === id ? null : s.activeUser,
+        }));
+        return true;
+      },
+    }),
+    {
+      name: 'user-store',
+      partialize: (state) => ({ activeUser: state.activeUser }),
+    },
+  ),
+);
+
+// Gibt die aktive User-ID zurück — wird von api/client.ts verwendet.
+export function getActiveUserId(): string | null {
+  const { activeUser } = useUserStore.getState();
+  return activeUser ? String(activeUser.id) : null;
+}
--- a/frontend/src/types/index.ts
+++ b/frontend/src/types/index.ts
@@ -121,6 +121,16 @@ export interface CreateSessionRequest {
  set_id: number;
 }

+export interface User {
+  id: number;
+  name: string;
+  created_at: string;
+}
+
+export interface CreateUserRequest {
+  name: string;
+}
+
 export interface CreateLogRequest {
  exercise_id: number;
  set_number: number;