diff --git a/CLAUDE.md b/CLAUDE.md
index 7589405..5bec388 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -39,7 +39,7 @@ src/intervalssync/
 
 - **`intervals_icu.py`** — shared upload, skip-existing (`external_id`), sport PUT, calendar workout fetch, sport-settings lookup (`fetch_sport_settings`, `max_hr`).
 - **`igpsport/core.py`** — `sync(SyncConfig, progress)`: login → list → FIT URL → download → upload. `external_id`: `igpsport_{ride_id}`.
-- **`igpsport/profile_sync.py`** — `sync_profile_zones`: intervals.icu sport settings → iGPSPORT profile thresholds/zones.
+- **`igpsport/profile_sync.py`** — `sync_profile_zones`: intervals.icu sport settings + athlete weight → iGPSPORT profile thresholds/zones/weight.
 - **`igpsport/workout.py`** — planned workouts intervals.icu → iGPSPORT.
 - **`bryton/ddp.py`** — Meteor DDP login + `activityList` subscription.
 - **`bryton/api.py`** — `GET https://m3.brytonactive.com/api/activity?id=…` (FIT download; Android app API).
diff --git a/README.md b/README.md
index 5b9b485..88b96a7 100644
--- a/README.md
+++ b/README.md
@@ -63,7 +63,7 @@
 - Optionally deletes the local `.fit` files after a successful upload
 - Stores your credentials in the **OS secure vault** (Windows Credential Manager / macOS Keychain / Android Keystore), never in a file
 - Lets you know when a newer version is available
-- **Sync zones to iGPSPORT** — push FTP, LTHR, max HR, and power/HR zones from intervals.icu into your iGPSPORT profile (Settings → iGPSPORT profile, or `intervalssync sync-zones`; the app prompts on launch when thresholds differ)
+- **Sync zones to iGPSPORT** — push FTP, LTHR, max HR, weight, and power/HR zones from intervals.icu into your iGPSPORT profile (Settings → iGPSPORT profile, or `intervalssync sync-zones`; the app prompts on launch when thresholds differ)
 - **Headless CLI** — activity sync, workout upload, and iGPSPORT zone/threshold sync from the terminal, with JSON output and exit codes for automation and AI agents (see [CLI & automation](#cli--automation-ai-agents))
 - **China iGPSPORT region** — accounts on [app.igpsport.cn](https://app.igpsport.cn/login) use a separate API; choose **China** in Settings (or `INTERVALSSYNC_IGPSPORT_REGION=china` in the CLI)
 
diff --git a/docs/AGENT.md b/docs/AGENT.md
index a413c14..691bf84 100644
--- a/docs/AGENT.md
+++ b/docs/AGENT.md
@@ -100,8 +100,8 @@ uv run intervalssync sync-zones --env-file .env --json
 ```
 
 - **iGPSPORT-only** (no `--source` flag)
-- Reads FTP, LTHR, max HR, power zones, and HR zones from intervals.icu `sport-settings/Ride` (override with `--sport`)
-- Writes them to iGPSPORT via the mobile `UserIntervalInfo` API
+- Reads FTP, LTHR, max HR, power zones, and HR zones from intervals.icu `sport-settings/Ride` (override with `--sport`), plus athlete weight (`icu_weight`) rounded to whole kg
+- Writes thresholds/zones via `UpdatePersonalIntervalInfo`, and weight via `User/UpdatePersonalUserInfo` (the endpoint the app profile editor uses)
 - Progress on **stderr**; result JSON on **stdout**; same exit codes as other commands
 
 Success example:
@@ -114,18 +114,21 @@ Success example:
     "ftp": 240,
     "lthr": 153,
     "mhr": 193,
+    "weight": 79.0,
     "power_zones": "0-132 | 132-180 | …",
     "hr_zones": "0-120 | …"
   },
   "ftp": 242,
   "lthr": 176,
   "mhr": 193,
+  "weight": 76.0,
   "power_zones": "0-133 | 133-182 | …",
   "hr_zones": "0-120 | 120-146 | …",
   "after": {
     "ftp": 242,
     "lthr": 176,
     "mhr": 193,
+    "weight": 76.0,
     "power_zones": "0-133 | 133-182 | …",
     "hr_zones": "0-120 | 120-146 | …"
   }
@@ -173,4 +176,4 @@ Same as GUI **Upload to iGPSPORT** / **Upload to Bryton** — intervals.icu cale
 
 ### Zone sync
 
-Reads FTP, LTHR, max HR, and power/HR zones from intervals.icu sport settings and writes them to the iGPSPORT profile (CLI only for now).
+Reads FTP, LTHR, max HR, power/HR zones, and weight from intervals.icu and writes them to the iGPSPORT profile (CLI only for now).
diff --git a/src/intervalssync/cli/main.py b/src/intervalssync/cli/main.py
index 54fe83a..1618429 100644
--- a/src/intervalssync/cli/main.py
+++ b/src/intervalssync/cli/main.py
@@ -608,7 +608,7 @@ def _build_parser() -> argparse.ArgumentParser:
     sync_zones_parser = subparsers.add_parser(
         "sync-zones",
         parents=[common],
-        help="Push FTP, LTHR, max HR, and zones from intervals.icu to iGPSPORT.",
+        help="Push FTP, LTHR, max HR, weight, and zones from intervals.icu to iGPSPORT.",
     )
     sync_zones_parser.add_argument(
         "--sport",
diff --git a/src/intervalssync/gui/config.py b/src/intervalssync/gui/config.py
index bea9ac9..d46a6f2 100644
--- a/src/intervalssync/gui/config.py
+++ b/src/intervalssync/gui/config.py
@@ -59,7 +59,7 @@ class AppConfig:
     workout_days_ahead: int = 1
     # intervals.icu threshold fingerprint the user declined to sync; cleared after sync.
     profile_sync_declined_fingerprint: str = ""
-    # Prompt on launch when FTP, LTHR, or max HR differ from intervals.icu.
+    # Prompt on launch when FTP, LTHR, max HR, or weight differ from intervals.icu.
     profile_sync_check_on_launch: bool = True
     # Lifetime sync stats (GUI gamification).
     lifetime_activities_uploaded: int = 0
diff --git a/src/intervalssync/gui/profile_sync_ui.py b/src/intervalssync/gui/profile_sync_ui.py
index 4a25333..7e15e58 100644
--- a/src/intervalssync/gui/profile_sync_ui.py
+++ b/src/intervalssync/gui/profile_sync_ui.py
@@ -109,6 +109,8 @@ def _sync_success_message(result: ProfileSyncResult) -> str:
     for key, label in (("ftp", "FTP"), ("lthr", "LTHR"), ("mhr", "max HR")):
         if key in member:
             parts.append(f"{label} {member[key]}")
+    if result.weight_after is not None:
+        parts.append(f"weight {result.weight_after}")
     if parts:
         return "iGPSPORT profile updated — " + ", ".join(parts) + "."
     return "iGPSPORT profile updated."
@@ -190,13 +192,13 @@ async def update_now(_: ft.ControlEvent) -> None:
                 spacing=theme.SPACE_SM,
                 controls=[
                     ft.Text(
-                        "Your iGPSPORT thresholds differ from intervals.icu:",
+                        "Your iGPSPORT profile differs from intervals.icu:",
                         size=13,
                         color=colors["text_muted"],
                     ),
                     *difference_lines,
                     ft.Text(
-                        "Power and heart-rate zones will be updated too.",
+                        "Power/HR zones and weight will be updated too.",
                         size=12,
                         color=colors["text_muted"],
                     ),
diff --git a/src/intervalssync/gui/settings_view.py b/src/intervalssync/gui/settings_view.py
index fc0bb82..119bf29 100644
--- a/src/intervalssync/gui/settings_view.py
+++ b/src/intervalssync/gui/settings_view.py
@@ -410,7 +410,7 @@ async def on_profile_tile_change(e: ft.ControlEvent) -> None:
     profile_sync_options = ft.ExpansionTile(
         title=ft.Text("iGPSPORT profile", weight=ft.FontWeight.W_500),
         subtitle=ft.Text(
-            "FTP, LTHR, max HR, and zones from intervals.icu",
+            "FTP, LTHR, max HR, weight, and zones from intervals.icu",
             size=12,
             color=colors["text_muted"],
         ),
diff --git a/src/intervalssync/igpsport/interval_info.py b/src/intervalssync/igpsport/interval_info.py
index 5e15d44..3b629e1 100644
--- a/src/intervalssync/igpsport/interval_info.py
+++ b/src/intervalssync/igpsport/interval_info.py
@@ -143,13 +143,117 @@ def update_personal_interval_info(
     return result if isinstance(result, dict) else {}
 
 
+def fetch_user_info(
+    session: requests.Session,
+    headers: dict[str, str],
+    region: IgpRegionConfig | str | None = None,
+) -> dict[str, Any]:
+    """GET User/UserInfo (profile fields including weight shown in the app)."""
+    cfg = resolve_region(region.name if isinstance(region, IgpRegionConfig) else region)
+    get_headers = {k: v for k, v in headers.items() if k.lower() != "content-type"}
+    try:
+        resp = session.get(cfg.user_info_url, headers=get_headers, timeout=30)
+    except requests.RequestException as exc:
+        raise RuntimeError(f"GET UserInfo failed: {exc}") from exc
+
+    try:
+        body = resp.json()
+    except ValueError as exc:
+        raise RuntimeError(
+            f"GET UserInfo: HTTP {resp.status_code}, non-JSON body"
+        ) from exc
+
+    if not isinstance(body, dict) or body.get("code") not in (0, None):
+        message = body.get("message") if isinstance(body, dict) else "unknown error"
+        raise RuntimeError(f"GET UserInfo failed: {message}")
+
+    data = body.get("data")
+    if not isinstance(data, dict):
+        raise RuntimeError("GET UserInfo: missing data object")
+    return data
+
+
+def build_personal_user_info_payload(
+    user_info: dict[str, Any],
+    weight_kg: int,
+) -> dict[str, Any]:
+    """Build the UpdatePersonalUserInfo body the iGPSPORT app sends.
+
+    Captured from the Android profile editor: a 6-field personal payload with
+    ``areaId`` (UserInfo ``cityId``) and ``gender`` (UserInfo ``sex``). Using
+    ``UpdateUserInfo`` with a full UserInfo merge clears location.
+    """
+    area_id = user_info.get("cityId")
+    if area_id in (None, "", 0, "0"):
+        area_id = user_info.get("areaId")
+    gender = user_info.get("gender")
+    if gender is None:
+        gender = user_info.get("sex")
+
+    return {
+        "areaId": int(area_id) if area_id not in (None, "") else 0,
+        "birthDate": user_info.get("birthDate") or "",
+        "gender": int(gender) if gender is not None else 0,
+        "height": int(user_info["height"]) if user_info.get("height") is not None else 0,
+        "nickName": user_info.get("nickName") or "",
+        # App sends a float (e.g. 76.0); whole-kg rounding happens before call.
+        "weight": float(int(weight_kg)),
+    }
+
+
+def update_user_weight(
+    session: requests.Session,
+    headers: dict[str, str],
+    weight_kg: int,
+    region: IgpRegionConfig | str | None = None,
+) -> dict[str, Any]:
+    """POST User/UpdatePersonalUserInfo with whole-kg weight (app profile weight).
+
+    Matches the Android editor: personal fields only, with ``areaId`` so location
+    is preserved. ``UpdateUserInfo`` clears ``cityId`` even when present in body.
+    """
+    cfg = resolve_region(region.name if isinstance(region, IgpRegionConfig) else region)
+    current = fetch_user_info(session, headers, region)
+    payload = build_personal_user_info_payload(current, weight_kg)
+
+    try:
+        resp = session.post(
+            cfg.update_personal_user_info_url,
+            headers=headers,
+            json=payload,
+            timeout=30,
+        )
+    except requests.RequestException as exc:
+        raise RuntimeError(f"POST UpdatePersonalUserInfo failed: {exc}") from exc
+
+    try:
+        result = resp.json()
+    except ValueError as exc:
+        raise RuntimeError(
+            f"POST UpdatePersonalUserInfo: HTTP {resp.status_code}, non-JSON body"
+        ) from exc
+
+    if not resp.ok:
+        raise RuntimeError(f"POST UpdatePersonalUserInfo: HTTP {resp.status_code}")
+
+    if isinstance(result, dict) and result.get("code") not in (0, None):
+        message = result.get("message") or "unknown error"
+        raise RuntimeError(f"POST UpdatePersonalUserInfo failed: {message}")
+
+    return result if isinstance(result, dict) else {}
+
+
 def zone_range_summary(zones: list[dict[str, Any]]) -> str:
     if not zones:
         return "(none)"
     return " | ".join(f"{z.get('start')}-{z.get('end')}" for z in zones)
 
 
-def profile_summary(body: dict[str, Any]) -> dict[str, Any]:
+def profile_summary(
+    body: dict[str, Any],
+    *,
+    weight: float | None = None,
+) -> dict[str, Any]:
     """Return a compact summary dict for CLI JSON output."""
     member = body.get("member") if isinstance(body.get("member"), dict) else {}
     power = body.get("power") if isinstance(body.get("power"), list) else []
@@ -158,6 +262,7 @@ def profile_summary(body: dict[str, Any]) -> dict[str, Any]:
         "ftp": member.get("ftp"),
         "lthr": member.get("lthr"),
         "mhr": member.get("mhr"),
+        "weight": weight if weight is not None else member.get("weight"),
         "heart_rate_compute_mode": member.get("heartRateComputeMode"),
         "power_zones": zone_range_summary(power),
         "hr_zones": zone_range_summary(heart_rate),
diff --git a/src/intervalssync/igpsport/profile_sync.py b/src/intervalssync/igpsport/profile_sync.py
index 898a73b..0b7d0b1 100644
--- a/src/intervalssync/igpsport/profile_sync.py
+++ b/src/intervalssync/igpsport/profile_sync.py
@@ -1,4 +1,4 @@
-"""Sync thresholds and zones from intervals.icu to iGPSPORT profile."""
+"""Sync thresholds, zones, and weight from intervals.icu to iGPSPORT profile."""
 
 from __future__ import annotations
 
@@ -15,10 +15,12 @@
 from .interval_info import (
     HEART_RATE_COMPUTE_MODE_MAX_HR,
     fetch_personal_interval_info,
+    fetch_user_info,
     mobile_headers,
     member_id_from_token,
     profile_summary,
     update_personal_interval_info,
+    update_user_weight,
     zone_range_summary,
 )
 from .zone_map import map_hr_zones, map_power_zones
@@ -43,6 +45,8 @@ class ProfileSyncConfig:
 class ProfileSyncResult:
     before: dict[str, Any] | None
     after: dict[str, Any] | None
+    weight_before: float | None = None
+    weight_after: float | None = None
 
 
 @dataclass
@@ -54,10 +58,27 @@ class ProfileThresholdStatus:
     igpsport: dict[str, int | None]
 
 
-_THRESHOLD_LABELS = {"ftp": "FTP", "lthr": "LTHR", "mhr": "max HR"}
+_THRESHOLD_LABELS = {"ftp": "FTP", "lthr": "LTHR", "mhr": "max HR", "weight": "Weight"}
 
 
-def _threshold_values(member: dict[str, Any]) -> dict[str, int | None]:
+def _whole_kg(value: Any) -> int | None:
+    """Round kg to a whole number; iGPSPORT only accepts integer kilograms."""
+    if value is None:
+        return None
+    try:
+        kg = int(round(float(value)))
+    except (TypeError, ValueError):
+        return None
+    if kg <= 0:
+        return None
+    return kg
+
+
+def _threshold_values(
+    member: dict[str, Any],
+    *,
+    weight: float | None = None,
+) -> dict[str, int | None]:
     def _int_val(key: str) -> int | None:
         value = member.get(key)
         if value is None:
@@ -71,38 +92,59 @@ def _int_val(key: str) -> int | None:
         "ftp": _int_val("ftp"),
         "lthr": _int_val("lthr"),
         "mhr": _int_val("mhr"),
+        # App profile weight comes from User/UserInfo, not UserIntervalInfo.member.
+        "weight": _whole_kg(weight),
     }
 
 
-def _threshold_fingerprint(settings: SportSettings) -> str:
+def _threshold_fingerprint(
+    settings: SportSettings,
+    weight: float | None = None,
+) -> str:
     ftp = int(round(settings.ftp or 0))
     mhr = int(round(settings.max_hr or 0))
     lthr = int(round(settings.lthr)) if settings.lthr is not None else ""
-    return f"{ftp}|{lthr}|{mhr}"
+    weight_part = _whole_kg(weight) if weight is not None else ""
+    return f"{ftp}|{lthr}|{mhr}|{weight_part}"
 
 
-def _intervals_threshold_values(settings: SportSettings) -> dict[str, int | None]:
+def _intervals_threshold_values(
+    settings: SportSettings,
+    weight: float | None = None,
+) -> dict[str, int | None]:
     return {
         "ftp": int(round(settings.ftp or 0)),
         "lthr": int(round(settings.lthr)) if settings.lthr is not None else None,
         "mhr": int(round(settings.max_hr or 0)),
+        "weight": _whole_kg(weight),
     }
 
 
 def compare_profile_thresholds(
     current: dict[str, Any],
     settings: SportSettings,
+    *,
+    weight: float | None = None,
+    current_weight: float | None = None,
 ) -> ProfileThresholdStatus:
-    """Return whether FTP, LTHR, or max HR would change on sync."""
+    """Return whether FTP, LTHR, max HR, or weight would change on sync."""
     desired = apply_intervals_settings(current, settings)
     member = current.get("member")
     desired_member = desired.get("member")
-    current_vals = _threshold_values(member if isinstance(member, dict) else {})
-    desired_vals = _threshold_values(desired_member if isinstance(desired_member, dict) else {})
+    current_vals = _threshold_values(
+        member if isinstance(member, dict) else {},
+        weight=current_weight,
+    )
+    desired_vals = _threshold_values(
+        desired_member if isinstance(desired_member, dict) else {},
+        weight=weight,
+    )
 
     keys_to_compare = ["ftp", "mhr"]
     if settings.lthr is not None:
         keys_to_compare.append("lthr")
+    if weight is not None and _whole_kg(weight) is not None:
+        keys_to_compare.append("weight")
 
     differences: list[str] = []
     for key in keys_to_compare:
@@ -116,8 +158,8 @@ def compare_profile_thresholds(
     return ProfileThresholdStatus(
         needs_sync=bool(differences),
         differences=differences,
-        intervals_fingerprint=_threshold_fingerprint(settings),
-        intervals=_intervals_threshold_values(settings),
+        intervals_fingerprint=_threshold_fingerprint(settings, weight),
+        intervals=_intervals_threshold_values(settings, weight),
         igpsport=current_vals,
     )
 
@@ -137,7 +179,11 @@ def apply_intervals_settings(
     body: dict[str, Any],
     settings: SportSettings,
 ) -> dict[str, Any]:
-    """Return a copy of the iGPSPORT payload with thresholds and zones updated."""
+    """Return a copy of the iGPSPORT payload with thresholds and zones updated.
+
+    Weight is updated separately via User/UpdatePersonalUserInfo — UpdatePersonalIntervalInfo
+    ignores member.weight.
+    """
     updated = copy.deepcopy(body)
     member = updated.get("member")
     if not isinstance(member, dict):
@@ -164,19 +210,25 @@ def apply_intervals_settings(
     return updated
 
 
-def _report_summary(report: Progress, label: str, body: dict[str, Any]) -> None:
+def _report_summary(
+    report: Progress,
+    label: str,
+    body: dict[str, Any],
+    *,
+    weight: float | None = None,
+) -> None:
     member = body.get("member") if isinstance(body.get("member"), dict) else {}
     power = body.get("power") if isinstance(body.get("power"), list) else []
     heart_rate = body.get("heartRate") if isinstance(body.get("heartRate"), list) else []
     report(f"{label}:")
-    report(
-        "  member: "
-        + ", ".join(
-            f"{key}={member[key]}"
-            for key in ("ftp", "mhr", "lthr", "heartRateComputeMode", "quietHeartRate")
-            if key in member
-        )
-    )
+    parts = [
+        f"{key}={member[key]}"
+        for key in ("ftp", "mhr", "lthr", "heartRateComputeMode", "quietHeartRate")
+        if key in member
+    ]
+    if weight is not None:
+        parts.append(f"weight={weight}")
+    report("  member: " + ", ".join(parts))
     report(f"  power:  {zone_range_summary(power)}")
     report(f"  heartRate: {zone_range_summary(heart_rate)}")
 
@@ -211,15 +263,33 @@ def sync_profile_zones(
 
     _validate_sport_settings(settings)
 
+    report("Fetching athlete weight from intervals.icu…")
+    try:
+        weight = intervals_icu.fetch_athlete_weight(
+            config.intervals_api_key,
+            http=session,
+        )
+    except requests.RequestException as exc:
+        raise SyncError(f"Could not fetch intervals.icu athlete weight: {exc}") from exc
+
     report("Fetching iGPSPORT profile…")
     try:
         current = fetch_personal_interval_info(session, headers, region)
+        user_info = fetch_user_info(session, headers, region)
     except RuntimeError as exc:
         raise SyncError(str(exc)) from exc
 
+    weight_before = user_info.get("weight")
+    target_weight = _whole_kg(weight)
+
     updated = apply_intervals_settings(current, settings)
-    _report_summary(report, "Before", current)
-    _report_summary(report, "After", updated)
+    _report_summary(report, "Before", current, weight=weight_before)
+    _report_summary(
+        report,
+        "After",
+        updated,
+        weight=float(target_weight) if target_weight is not None else weight_before,
+    )
 
     report("Updating iGPSPORT profile…")
     try:
@@ -227,14 +297,37 @@ def sync_profile_zones(
     except RuntimeError as exc:
         raise SyncError(str(exc)) from exc
 
+    if target_weight is not None and _whole_kg(weight_before) != target_weight:
+        saved_city_id = user_info.get("cityId")
+        report("Updating iGPSPORT weight…")
+        try:
+            update_user_weight(session, headers, target_weight, region)
+        except RuntimeError as exc:
+            raise SyncError(str(exc)) from exc
+        user_info_after_weight = fetch_user_info(session, headers, region)
+        city_after = user_info_after_weight.get("cityId")
+        if saved_city_id not in (None, 0, "0") and city_after in (None, 0, "", "0"):
+            report(
+                "Note: iGPSPORT cleared profile location while updating weight; "
+                "set location again in the app."
+            )
+
     report("Verifying iGPSPORT profile…")
     try:
-        after = fetch_personal_interval_info(session, headers)
+        after = fetch_personal_interval_info(session, headers, region)
+        user_info_after = fetch_user_info(session, headers, region)
     except RuntimeError as exc:
         raise SyncError(str(exc)) from exc
 
-    _report_summary(report, "Read-back", after)
-    return ProfileSyncResult(before=current, after=after)
+    weight_after = user_info_after.get("weight")
+
+    _report_summary(report, "Read-back", after, weight=weight_after)
+    return ProfileSyncResult(
+        before=current,
+        after=after,
+        weight_before=float(weight_before) if weight_before is not None else None,
+        weight_after=float(weight_after) if weight_after is not None else None,
+    )
 
 
 def fetch_profile_threshold_status(config: ProfileSyncConfig) -> ProfileThresholdStatus:
@@ -260,12 +353,26 @@ def fetch_profile_threshold_status(config: ProfileSyncConfig) -> ProfileThreshol
 
     _validate_sport_settings(settings)
 
+    try:
+        weight = intervals_icu.fetch_athlete_weight(
+            config.intervals_api_key,
+            http=session,
+        )
+    except requests.RequestException as exc:
+        raise SyncError(f"Could not fetch intervals.icu athlete weight: {exc}") from exc
+
     try:
         current = fetch_personal_interval_info(session, headers, region)
+        user_info = fetch_user_info(session, headers, region)
     except RuntimeError as exc:
         raise SyncError(str(exc)) from exc
 
-    return compare_profile_thresholds(current, settings)
+    return compare_profile_thresholds(
+        current,
+        settings,
+        weight=weight,
+        current_weight=user_info.get("weight"),
+    )
 
 
 def result_payload(result: ProfileSyncResult, *, ok: bool, error: str | None = None) -> dict[str, Any]:
@@ -274,9 +381,9 @@ def result_payload(result: ProfileSyncResult, *, ok: bool, error: str | None = N
         "source": "igpsport",
     }
     if result.before is not None:
-        payload["before"] = profile_summary(result.before)
+        payload["before"] = profile_summary(result.before, weight=result.weight_before)
     if result.after is not None:
-        summary = profile_summary(result.after)
+        summary = profile_summary(result.after, weight=result.weight_after)
         payload.update(summary)
         payload["after"] = summary
     if error is not None:
diff --git a/src/intervalssync/igpsport/region.py b/src/intervalssync/igpsport/region.py
index 680fc1b..4164d80 100644
--- a/src/intervalssync/igpsport/region.py
+++ b/src/intervalssync/igpsport/region.py
@@ -33,6 +33,15 @@ def get_interval_url(self) -> str:
     def update_interval_url(self) -> str:
         return f"{self.mobile_api_base}/User/UpdatePersonalIntervalInfo"
 
+    @property
+    def user_info_url(self) -> str:
+        return f"{self.mobile_api_base}/User/UserInfo"
+
+    @property
+    def update_personal_user_info_url(self) -> str:
+        # App profile editor saves weight/height/etc here (not UpdateUserInfo).
+        return f"{self.mobile_api_base}/User/UpdatePersonalUserInfo"
+
 
 INTERNATIONAL = IgpRegionConfig(
     name="international",
diff --git a/src/intervalssync/intervals_icu.py b/src/intervalssync/intervals_icu.py
index cbcdb38..d890b1b 100644
--- a/src/intervalssync/intervals_icu.py
+++ b/src/intervalssync/intervals_icu.py
@@ -17,6 +17,7 @@
 INTERVALS_ACTIVITY_URL = "https://intervals.icu/api/v1/activity"
 INTERVALS_EVENTS_URL = "https://intervals.icu/api/v1/athlete/0/events"
 INTERVALS_SPORT_SETTINGS_URL = "https://intervals.icu/api/v1/athlete/0/sport-settings"
+INTERVALS_ATHLETE_URL = "https://intervals.icu/api/v1/athlete/0"
 
 
 @dataclass
@@ -175,3 +176,22 @@ def fetch_sport_settings_max_hr(
 ) -> float | None:
     """Return athlete max HR (bpm) from intervals.icu sport settings."""
     return fetch_sport_settings(api_key, sport, http=http).max_hr
+
+
+def fetch_athlete_weight(
+    api_key: str,
+    *,
+    http: requests.Session | None = None,
+) -> float | None:
+    """Return athlete weight in kg from intervals.icu (`icu_weight`, else `weight`)."""
+    client = http or requests.Session()
+    resp = client.get(
+        INTERVALS_ATHLETE_URL,
+        auth=("API_KEY", api_key),
+        timeout=30,
+    )
+    resp.raise_for_status()
+    data = resp.json()
+    if not isinstance(data, dict):
+        return None
+    return _num(data.get("icu_weight")) or _num(data.get("weight"))
diff --git a/tests/test_intervals_icu.py b/tests/test_intervals_icu.py
index 009b3c1..d2212ae 100644
--- a/tests/test_intervals_icu.py
+++ b/tests/test_intervals_icu.py
@@ -85,3 +85,35 @@ def test_fetch_sport_settings(monkeypatch):
     assert settings.max_hr == 193.0
     assert settings.power_zones == [55.0, 75.0, 90.0, 105.0, 120.0, 999.0]
     assert settings.hr_zones == [120.0, 146.0, 166.0, 185.0, 193.0]
+
+
+def test_fetch_athlete_weight_prefers_icu_weight(monkeypatch):
+    captured: dict = {}
+
+    def fake_get(self, url, auth, timeout):
+        captured["url"] = url
+        captured["auth"] = auth
+        return FakeResponse(json_data={"icu_weight": 76.1, "weight": 70.0})
+
+    monkeypatch.setattr(intervals_icu.requests.Session, "get", fake_get)
+    assert intervals_icu.fetch_athlete_weight("api-key") == 76.1
+    assert captured["url"].endswith("/athlete/0")
+    assert captured["auth"] == ("API_KEY", "api-key")
+
+
+def test_fetch_athlete_weight_falls_back_to_weight(monkeypatch):
+    monkeypatch.setattr(
+        intervals_icu.requests.Session,
+        "get",
+        lambda self, *a, **k: FakeResponse(json_data={"weight": 72.5}),
+    )
+    assert intervals_icu.fetch_athlete_weight("api-key") == 72.5
+
+
+def test_fetch_athlete_weight_missing(monkeypatch):
+    monkeypatch.setattr(
+        intervals_icu.requests.Session,
+        "get",
+        lambda self, *a, **k: FakeResponse(json_data={"name": "Athlete"}),
+    )
+    assert intervals_icu.fetch_athlete_weight("api-key") is None
diff --git a/tests/test_profile_sync.py b/tests/test_profile_sync.py
index 0d099d4..3ca5bb0 100644
--- a/tests/test_profile_sync.py
+++ b/tests/test_profile_sync.py
@@ -38,6 +38,7 @@ def test_apply_intervals_settings_updates_thresholds_and_zones():
     assert updated["member"]["lthr"] == 176
     assert updated["member"]["mhr"] == 193
     assert updated["member"]["heartRateComputeMode"] == 0
+    assert "weight" not in updated["member"]
     assert len(updated["power"]) == 7
     assert updated["power"][0]["end"] == 133
     assert updated["power"][-1]["end"] == 2500
@@ -66,10 +67,12 @@ def _ride_settings(**overrides: object) -> SportSettings:
 
 def test_compare_profile_thresholds_in_sync():
     body = apply_intervals_settings(_igpsport_payload(), _ride_settings())
-    status = compare_profile_thresholds(body, _ride_settings())
+    status = compare_profile_thresholds(
+        body, _ride_settings(), weight=79.0, current_weight=79.0
+    )
     assert status.needs_sync is False
     assert status.differences == []
-    assert status.intervals_fingerprint == "242|176|193"
+    assert status.intervals_fingerprint == "242|176|193|79"
 
 
 def test_compare_profile_thresholds_ftp_mismatch():
@@ -77,6 +80,7 @@ def test_compare_profile_thresholds_ftp_mismatch():
     assert status.needs_sync is True
     assert len(status.differences) == 3
     assert status.differences[0].startswith("FTP:")
+    assert status.intervals_fingerprint == "242|176|193|"
 
 
 def test_compare_profile_thresholds_lthr_mismatch_only():
@@ -97,6 +101,124 @@ def test_compare_profile_thresholds_mhr_mismatch_only():
     assert status.differences == ["max HR: iGPSPORT 190 → intervals.icu 193"]
 
 
+def test_build_personal_user_info_payload_maps_city_and_sex():
+    from intervalssync.igpsport.interval_info import build_personal_user_info_payload
+
+    payload = build_personal_user_info_payload(
+        {
+            "cityId": 103172,
+            "cityName": "Braga",
+            "sex": 1,
+            "height": 179,
+            "nickName": "Jorge Silva",
+            "birthDate": "1998-08-17",
+            "weight": 79.0,
+            "ftp": 242,
+            "avatar": "https://example.com/a.png",
+        },
+        76,
+    )
+    assert payload == {
+        "areaId": 103172,
+        "birthDate": "1998-08-17",
+        "gender": 1,
+        "height": 179,
+        "nickName": "Jorge Silva",
+        "weight": 76.0,
+    }
+
+
+def test_build_personal_user_info_payload_prefers_area_id_and_gender():
+    from intervalssync.igpsport.interval_info import build_personal_user_info_payload
+
+    payload = build_personal_user_info_payload(
+        {
+            "cityId": 0,
+            "areaId": 1101172,
+            "gender": 1,
+            "sex": 0,
+            "height": 179,
+            "nickName": "Jorge",
+            "birthDate": "1998-08-17",
+        },
+        76,
+    )
+    assert payload["areaId"] == 1101172
+    assert payload["gender"] == 1
+    assert payload["weight"] == 76.0
+
+
+def test_update_user_weight_posts_personal_user_info(monkeypatch):
+    from intervalssync.igpsport import interval_info
+
+    posted: dict = {}
+
+    class FakeResp:
+        ok = True
+        status_code = 200
+
+        def json(self):
+            return {"code": 0, "data": True}
+
+    class FakeSession:
+        def post(self, url, headers=None, json=None, timeout=None):
+            posted["url"] = url
+            posted["json"] = json
+            return FakeResp()
+
+    monkeypatch.setattr(
+        interval_info,
+        "fetch_user_info",
+        lambda *a, **k: {
+            "cityId": 103172,
+            "cityName": "Braga",
+            "sex": 1,
+            "height": 179,
+            "nickName": "Jorge Silva",
+            "birthDate": "1998-08-17",
+            "weight": 79.0,
+        },
+    )
+
+    result = interval_info.update_user_weight(FakeSession(), {"Authorization": "Bearer x"}, 76)
+    assert result["code"] == 0
+    assert posted["url"].endswith("/User/UpdatePersonalUserInfo")
+    assert posted["json"] == {
+        "areaId": 103172,
+        "birthDate": "1998-08-17",
+        "gender": 1,
+        "height": 179,
+        "nickName": "Jorge Silva",
+        "weight": 76.0,
+    }
+
+    body = apply_intervals_settings(_igpsport_payload(), _ride_settings())
+    status = compare_profile_thresholds(
+        body, _ride_settings(), weight=76.1, current_weight=79.0
+    )
+    assert status.needs_sync is True
+    assert status.differences == ["Weight: iGPSPORT 79 → intervals.icu 76"]
+    assert status.intervals_fingerprint == "242|176|193|76"
+
+
+def test_compare_profile_thresholds_weight_fractional_matches_after_round():
+    body = apply_intervals_settings(_igpsport_payload(), _ride_settings())
+    status = compare_profile_thresholds(
+        body, _ride_settings(), weight=76.4, current_weight=76.0
+    )
+    assert status.needs_sync is False
+    assert status.intervals_fingerprint == "242|176|193|76"
+
+
+def test_compare_profile_thresholds_skips_weight_when_intervals_missing():
+    body = apply_intervals_settings(_igpsport_payload(), _ride_settings())
+    status = compare_profile_thresholds(
+        body, _ride_settings(), weight=None, current_weight=79.0
+    )
+    assert status.needs_sync is False
+    assert status.intervals_fingerprint == "242|176|193|"
+
+
 def test_compare_profile_thresholds_skips_lthr_when_intervals_missing():
     body = _igpsport_payload()
     body["member"]["ftp"] = 242
@@ -104,7 +226,7 @@ def test_compare_profile_thresholds_skips_lthr_when_intervals_missing():
     settings = _ride_settings(lthr=None)
     status = compare_profile_thresholds(body, settings)
     assert status.needs_sync is False
-    assert status.intervals_fingerprint == "242||193"
+    assert status.intervals_fingerprint == "242||193|"
 
 
 def test_fetch_profile_threshold_status(monkeypatch):
@@ -120,23 +242,35 @@ def test_fetch_profile_threshold_status(monkeypatch):
         "fetch_sport_settings",
         lambda *a, **k: settings,
     )
+    monkeypatch.setattr(
+        profile_sync.intervals_icu,
+        "fetch_athlete_weight",
+        lambda *a, **k: 76.1,
+    )
     monkeypatch.setattr(
         profile_sync,
         "fetch_personal_interval_info",
         lambda *a, **k: current,
     )
+    monkeypatch.setattr(
+        profile_sync,
+        "fetch_user_info",
+        lambda *a, **k: {"weight": 79.0},
+    )
 
     status = profile_sync.fetch_profile_threshold_status(
         ProfileSyncConfig("user", "pass", "api-key"),
     )
     assert status.needs_sync is True
     assert any(diff.startswith("FTP:") for diff in status.differences)
+    assert any(diff.startswith("Weight:") for diff in status.differences)
 
 
 def test_sync_profile_zones_end_to_end(monkeypatch):
     from intervalssync.igpsport import profile_sync
 
     posted: dict = {}
+    weight_posts: list[int] = []
 
     settings = SportSettings(
         ftp=242,
@@ -154,19 +288,35 @@ def test_sync_profile_zones_end_to_end(monkeypatch):
         "fetch_sport_settings",
         lambda *a, **k: settings,
     )
+    monkeypatch.setattr(
+        profile_sync.intervals_icu,
+        "fetch_athlete_weight",
+        lambda *a, **k: 76.1,
+    )
 
     calls = {"get": 0}
+    userinfo_weight = {"value": 79.0}
 
     def fake_fetch(session, headers, *args, **kwargs):
         calls["get"] += 1
         return current if calls["get"] == 1 else apply_intervals_settings(current, settings)
 
+    def fake_user_info(session, headers, *args, **kwargs):
+        return {"weight": userinfo_weight["value"]}
+
     def fake_update(session, headers, body, *args, **kwargs):
         posted["body"] = body
         return {"code": 0}
 
+    def fake_update_weight(session, headers, weight_kg, *args, **kwargs):
+        weight_posts.append(weight_kg)
+        userinfo_weight["value"] = float(weight_kg)
+        return {"code": 0}
+
     monkeypatch.setattr(profile_sync, "fetch_personal_interval_info", fake_fetch)
+    monkeypatch.setattr(profile_sync, "fetch_user_info", fake_user_info)
     monkeypatch.setattr(profile_sync, "update_personal_interval_info", fake_update)
+    monkeypatch.setattr(profile_sync, "update_user_weight", fake_update_weight)
 
     result = profile_sync.sync_profile_zones(
         ProfileSyncConfig("user", "pass", "api-key"),
@@ -174,5 +324,57 @@ def fake_update(session, headers, body, *args, **kwargs):
     )
 
     assert posted["body"]["member"]["ftp"] == 242
+    assert "weight" not in posted["body"]["member"] or posted["body"]["member"].get("weight") != 76.0
+    assert weight_posts == [76]
     assert result.after is not None
     assert result.after["member"]["mhr"] == 193
+    assert result.weight_before == 79.0
+    assert result.weight_after == 76.0
+
+
+def test_sync_profile_zones_skips_weight_update_when_unchanged(monkeypatch):
+    from intervalssync.igpsport import profile_sync
+
+    settings = _ride_settings()
+    current = apply_intervals_settings(_igpsport_payload(), settings)
+    weight_posts: list[int] = []
+
+    monkeypatch.setattr(profile_sync, "login", lambda *a, **k: {"Authorization": "Bearer x"})
+    monkeypatch.setattr(profile_sync, "member_id_from_token", lambda *a, **k: 1171353)
+    monkeypatch.setattr(
+        profile_sync.intervals_icu,
+        "fetch_sport_settings",
+        lambda *a, **k: settings,
+    )
+    monkeypatch.setattr(
+        profile_sync.intervals_icu,
+        "fetch_athlete_weight",
+        lambda *a, **k: 76.0,
+    )
+    monkeypatch.setattr(
+        profile_sync,
+        "fetch_personal_interval_info",
+        lambda *a, **k: current,
+    )
+    monkeypatch.setattr(
+        profile_sync,
+        "fetch_user_info",
+        lambda *a, **k: {"weight": 76.0, "cityId": 103172, "cityName": "Braga"},
+    )
+    monkeypatch.setattr(
+        profile_sync,
+        "update_personal_interval_info",
+        lambda *a, **k: {"code": 0},
+    )
+    monkeypatch.setattr(
+        profile_sync,
+        "update_user_weight",
+        lambda *a, **k: weight_posts.append(a[2]),
+    )
+
+    result = profile_sync.sync_profile_zones(
+        ProfileSyncConfig("user", "pass", "api-key"),
+        progress=lambda _message: None,
+    )
+    assert weight_posts == []
+    assert result.weight_after == 76.0