diff --git a/backend/app/api/profile.py b/backend/app/api/profile.py
index b061606..7668676 100644
--- a/backend/app/api/profile.py
+++ b/backend/app/api/profile.py
@@ -19,6 +19,7 @@ class ProfileUpdate(BaseModel):
     resting_heart_rate: Optional[int] = None
     birth_year: Optional[int] = None
     height_cm: Optional[float] = None
+    biological_sex: Optional[str] = None
 
 
 class ProfileOut(BaseModel):
@@ -29,6 +30,7 @@ class ProfileOut(BaseModel):
     resting_heart_rate: Optional[int]
     birth_year: Optional[int]
     height_cm: Optional[float]
+    biological_sex: Optional[str]
     estimated_max_hr: Optional[int]
     is_admin: bool
 
@@ -72,6 +74,10 @@ async def update_profile(
         if not (50 <= body.height_cm <= 300):
             raise HTTPException(400, "Height must be 50–300 cm")
         current_user.height_cm = body.height_cm
+    if body.biological_sex is not None:
+        if body.biological_sex not in ('male', 'female', ''):
+            raise HTTPException(400, "biological_sex must be 'male' or 'female'")
+        current_user.biological_sex = body.biological_sex or None
 
     await db.commit()
     await db.refresh(current_user)
diff --git a/backend/app/main.py b/backend/app/main.py
index 2861843..b6b5174 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -64,6 +64,15 @@ async def init_db():
     except Exception as e:
         print(f"health_metrics column migration skipped: {e}")
 
+    # biological_sex column on users added after initial creation
+    try:
+        async with engine.begin() as conn:
+            await conn.execute(text(
+                "ALTER TABLE users ADD COLUMN IF NOT EXISTS biological_sex VARCHAR(8)"
+            ))
+    except Exception as e:
+        print(f"users.biological_sex column migration skipped: {e}")
+
     # route_segments auto_generated column added after initial creation
     try:
         async with engine.begin() as conn:
diff --git a/backend/app/models/user.py b/backend/app/models/user.py
index f2b0a61..bf6c9f0 100644
--- a/backend/app/models/user.py
+++ b/backend/app/models/user.py
@@ -27,6 +27,7 @@ class User(Base):
     resting_heart_rate = Column(Integer, nullable=True)
     birth_year = Column(Integer, nullable=True)
     height_cm = Column(Float, nullable=True)
+    biological_sex = Column(String(8), nullable=True)   # 'male' | 'female'
 
     # PocketID config (stored per-user so admin can set via UI)
     pocketid_issuer = Column(String(512), nullable=True)
diff --git a/frontend/src/pages/HealthPage.jsx b/frontend/src/pages/HealthPage.jsx
index ae1a002..6e4ac3b 100644
--- a/frontend/src/pages/HealthPage.jsx
+++ b/frontend/src/pages/HealthPage.jsx
@@ -9,14 +9,124 @@ import api from '../utils/api'
 import { formatSleep, sportIcon } from '../utils/format'
 
 const RANGES = [
-  { label: '1W', days: 7 },
-  { label: '2W', days: 14 },
-  { label: '1M', days: 30 },
-  { label: '3M', days: 90 },
-  { label: '6M', days: 180 },
-  { label: '1Y', days: 365 },
+  { label: '1W',  days: 7 },
+  { label: '2W',  days: 14 },
+  { label: '1M',  days: 30 },
+  { label: '3M',  days: 90 },
+  { label: '6M',  days: 180 },
+  { label: '1Y',  days: 365 },
+  { label: '3Y',  days: 1095 },
+  { label: '5Y',  days: 1825 },
 ]
 
+// ── VO2 Max gauge ────────────────────────────────────────────────────────────
+
+// ACSM sex-specific VO2 max thresholds
+// [maxAge, [veryPoor_max, poor_max, fair_max, good_max]]  (above good_max → Excellent)
+const VO2_MALE = [
+  [29, [32, 36, 41, 45]],
+  [39, [30, 34, 38, 43]],
+  [49, [29, 33, 37, 42]],
+  [59, [25, 30, 34, 38]],
+  [69, [20, 24, 28, 32]],
+  [Infinity, [17, 21, 24, 28]],
+]
+const VO2_FEMALE = [
+  [29, [27, 33, 36, 41]],
+  [39, [26, 30, 35, 39]],
+  [49, [24, 28, 32, 36]],
+  [59, [21, 24, 28, 32]],
+  [69, [18, 21, 24, 28]],
+  [Infinity, [15, 18, 22, 25]],
+]
+const VO2_CATEGORIES = [
+  { label: 'Very Poor', color: '#ef4444' },
+  { label: 'Poor',      color: '#f97316' },
+  { label: 'Fair',      color: '#22c55e' },
+  { label: 'Good',      color: '#3b82f6' },
+  { label: 'Excellent', color: '#a855f7' },
+]
+
+function getVo2Category(value, age, sex) {
+  const table = sex === 'female' ? VO2_FEMALE : VO2_MALE
+  const row = table.find(([maxAge]) => age <= maxAge) || table[table.length - 1]
+  const thresholds = row[1]
+  const idx = thresholds.findIndex(t => value <= t)
+  return idx === -1 ? VO2_CATEGORIES[4] : VO2_CATEGORIES[idx]
+}
+
+function arcPath(cx, cy, r, startDeg, endDeg) {
+  const toRad = d => (d - 90) * Math.PI / 180
+  const x1 = cx + r * Math.cos(toRad(startDeg))
+  const y1 = cy + r * Math.sin(toRad(startDeg))
+  const x2 = cx + r * Math.cos(toRad(endDeg))
+  const y2 = cy + r * Math.sin(toRad(endDeg))
+  const large = endDeg - startDeg > 180 ? 1 : 0
+  return `M ${x1} ${y1} A ${r} ${r} 0 ${large} 1 ${x2} ${y2}`
+}
+
+function Vo2MaxGauge({ value, birthYear, biologicalSex }) {
+  const age = birthYear ? new Date().getFullYear() - birthYear : 40
+  const cat = value != null ? getVo2Category(value, age, biologicalSex) : null
+
+  // Gauge spans 180° — from 180° (9 o'clock) to 360° (3 o'clock) across the top
+  const cx = 70, cy = 72, r = 52, sw = 14
+  const startDeg = 180, totalDeg = 180
+  const segDeg = totalDeg / 5
+
+  // Compute value angle for needle
+  let needleAngle = null
+  if (value != null) {
+    const table = biologicalSex === 'female' ? VO2_FEMALE : VO2_MALE
+    const row = table.find(([maxAge]) => age <= maxAge) || table[table.length - 1]
+    const thresholds = row[1]
+    const rangeMin = thresholds[0] - 8   // below Very Poor threshold
+    const rangeMax = thresholds[3] + 12  // above Good threshold (Excellent zone)
+    const pct = Math.max(0, Math.min(1, (value - rangeMin) / (rangeMax - rangeMin)))
+    needleAngle = startDeg + pct * totalDeg
+  }
+
+  return (
+    <div className="flex flex-col items-center">
+      <svg width="140" height="80" viewBox="0 0 140 80">
+        {/* Background track */}
+        <path d={arcPath(cx, cy, r, startDeg, startDeg + totalDeg)}
+          stroke="#1f2937" strokeWidth={sw} fill="none" strokeLinecap="butt" />
+        {/* 5 coloured category segments */}
+        {VO2_CATEGORIES.map((c, i) => (
+          <path key={i}
+            d={arcPath(cx, cy, r, startDeg + i * segDeg, startDeg + (i + 1) * segDeg)}
+            stroke={c.color} strokeWidth={sw} fill="none" strokeLinecap="butt"
+            strokeOpacity={0.25}
+          />
+        ))}
+        {/* Filled arc up to current value */}
+        {needleAngle != null && needleAngle > startDeg && (
+          <path d={arcPath(cx, cy, r, startDeg, needleAngle)}
+            stroke={cat?.color} strokeWidth={sw} fill="none" strokeLinecap="butt" />
+        )}
+        {/* Needle dot */}
+        {needleAngle != null && (() => {
+          const toRad = d => (d - 90) * Math.PI / 180
+          const nx = cx + r * Math.cos(toRad(needleAngle))
+          const ny = cy + r * Math.sin(toRad(needleAngle))
+          return <circle cx={nx} cy={ny} r={5} fill={cat?.color} />
+        })()}
+        {/* Value */}
+        <text x={cx} y={cy - 6} textAnchor="middle" dominantBaseline="middle"
+          fontSize="22" fontWeight="700" fill={cat?.color ?? '#6b7280'}>
+          {value != null ? value.toFixed(1) : '--'}
+        </text>
+        {/* Category label */}
+        <text x={cx} y={cy + 14} textAnchor="middle" dominantBaseline="middle"
+          fontSize="9" fill="#9ca3af">
+          {cat?.label ?? (biologicalSex ? '' : 'Set sex in profile')}
+        </text>
+      </svg>
+    </div>
+  )
+}
+
 const tooltipStyle = {
   background: '#111827', border: '1px solid #374151', borderRadius: 8, fontSize: 12,
 }
@@ -304,7 +414,7 @@ function NavArrow({ onClick, disabled, children }) {
   )
 }
 
-function DailySnapshot({ day, avg30, intradayHr, bodyBattery, bbHires, sleepStages, activities, latestVo2max, onOlder, onNewer, hasOlder, hasNewer }) {
+function DailySnapshot({ day, avg30, intradayHr, bodyBattery, bbHires, sleepStages, activities, latestVo2max, birthYear, biologicalSex, onOlder, onNewer, hasOlder, hasNewer }) {
   if (!day) return (
     <div className="text-center py-10 text-gray-600">
       <p className="text-3xl mb-2">📊</p>
@@ -341,9 +451,9 @@ function DailySnapshot({ day, avg30, intradayHr, bodyBattery, bbHires, sleepStag
       </div>
 
       {/* Sleep (wide) + Heart / HRV */}
-      <div className="grid grid-cols-1 lg:grid-cols-3 gap-4">
+      <div className="grid grid-cols-1 lg:grid-cols-2 gap-4">
 
-        <div className="lg:col-span-2 bg-gray-900 rounded-xl border border-gray-800 p-5 space-y-3">
+        <div className="bg-gray-900 rounded-xl border border-gray-800 p-5 space-y-3">
           <div className="flex items-center justify-between">
             <h3 className="text-sm font-medium text-gray-300">Sleep</h3>
             {day.sleep_score != null && (
@@ -396,56 +506,58 @@ function DailySnapshot({ day, avg30, intradayHr, bodyBattery, bbHires, sleepStag
           ) : null}
         </div>
 
-        <div className="bg-gray-900 rounded-xl border border-gray-800 p-5 space-y-4">
-          <h3 className="text-sm font-medium text-gray-300">Heart & HRV</h3>
-          <div>
-            <p className="text-xs text-gray-500 mb-0.5">Resting HR</p>
-            <div className="flex items-baseline gap-1.5">
-              <span className="text-3xl font-bold text-rose-400">
-                {day.resting_hr ? Math.round(day.resting_hr) : '--'}
-              </span>
-              <span className="text-sm text-gray-500">bpm</span>
+        <div className="bg-gray-900 rounded-xl border border-gray-800 p-5">
+          <h3 className="text-sm font-medium text-gray-300 mb-3">Heart & HRV</h3>
+          <div className="grid grid-cols-2 gap-x-4 gap-y-3">
+            <div>
+              <p className="text-xs text-gray-500 mb-0.5">Resting HR</p>
+              <div className="flex items-baseline gap-1.5">
+                <span className="text-3xl font-bold text-rose-400">
+                  {day.resting_hr ? Math.round(day.resting_hr) : '--'}
+                </span>
+                <span className="text-sm text-gray-500">bpm</span>
+              </div>
+              {avg30?.resting_hr && day.resting_hr && (
+                <p className="text-xs text-gray-500 mt-0.5">
+                  30d avg {Math.round(avg30.resting_hr)}
+                  {day.resting_hr < avg30.resting_hr
+                    ? <span className="text-green-400 ml-1">↓</span>
+                    : day.resting_hr > avg30.resting_hr
+                    ? <span className="text-red-400 ml-1">↑</span>
+                    : null}
+                </p>
+              )}
             </div>
-            {avg30?.resting_hr && day.resting_hr && (
-              <p className="text-xs text-gray-500 mt-0.5">
-                30d avg {Math.round(avg30.resting_hr)} bpm
-                {day.resting_hr < avg30.resting_hr
-                  ? <span className="text-green-400 ml-1">↓</span>
-                  : day.resting_hr > avg30.resting_hr
-                  ? <span className="text-red-400 ml-1">↑</span>
-                  : null}
-              </p>
-            )}
-          </div>
-          <div>
-            <p className="text-xs text-gray-500 mb-0.5">HRV</p>
-            <div className="flex items-baseline gap-1.5 flex-wrap">
-              <span className="text-3xl font-bold text-violet-400">
-                {day.hrv_nightly_avg ? Math.round(day.hrv_nightly_avg) : '--'}
-              </span>
-              <span className="text-sm text-gray-500">ms</span>
-              <HrvBadge status={day.hrv_status} />
+            <div>
+              <p className="text-xs text-gray-500 mb-0.5">HRV</p>
+              <div className="flex items-baseline gap-1.5 flex-wrap">
+                <span className="text-3xl font-bold text-violet-400">
+                  {day.hrv_nightly_avg ? Math.round(day.hrv_nightly_avg) : '--'}
+                </span>
+                <span className="text-sm text-gray-500">ms</span>
+              </div>
+              <div className="mt-0.5"><HrvBadge status={day.hrv_status} /></div>
             </div>
-          </div>
-          {day.avg_hr_day && (
             <div>
               <p className="text-xs text-gray-500 mb-0.5">Avg HR (day)</p>
               <div className="flex items-baseline gap-1.5">
-                <span className="text-xl font-semibold text-orange-400">{Math.round(day.avg_hr_day)}</span>
-                {day.max_hr_day && <span className="text-xs text-gray-500">/ {Math.round(day.max_hr_day)} max bpm</span>}
+                <span className="text-xl font-semibold text-orange-400">
+                  {day.avg_hr_day ? Math.round(day.avg_hr_day) : '--'}
+                </span>
+                {day.max_hr_day && <span className="text-xs text-gray-500">/ {Math.round(day.max_hr_day)} max</span>}
               </div>
             </div>
-          )}
-          {day.weight_kg && (
             <div>
               <p className="text-xs text-gray-500 mb-0.5">Weight</p>
               <div className="flex items-baseline gap-1.5 flex-wrap">
-                <span className="text-xl font-semibold text-emerald-400">{day.weight_kg.toFixed(1)}</span>
-                <span className="text-xs text-gray-500">kg</span>
+                <span className="text-xl font-semibold text-emerald-400">
+                  {day.weight_kg ? day.weight_kg.toFixed(1) : '--'}
+                </span>
+                {day.weight_kg && <span className="text-xs text-gray-500">kg</span>}
                 {day.body_fat_pct && <span className="text-xs text-gray-500">{day.body_fat_pct.toFixed(1)}% fat</span>}
               </div>
             </div>
-          )}
+          </div>
         </div>
       </div>
 
@@ -519,14 +631,16 @@ function DailySnapshot({ day, avg30, intradayHr, bodyBattery, bbHires, sleepStag
           {stressLabel && <p className="text-xs text-gray-500 mt-1">{stressLabel}</p>}
         </div>
 
-        <div className="bg-gray-900 rounded-xl border border-gray-800 p-4">
+        <div className="bg-gray-900 rounded-xl border border-gray-800 p-4 flex flex-col">
           <p className="text-xs text-gray-500 mb-1">VO2 Max</p>
-          <div className="flex items-baseline gap-1">
-            <span className="text-2xl font-bold text-blue-400">
-              {(day.vo2max ?? latestVo2max) != null ? (day.vo2max ?? latestVo2max).toFixed(1) : '--'}
-            </span>
+          <div className="flex-1 flex items-center justify-center">
+            <Vo2MaxGauge
+              value={(day.vo2max ?? latestVo2max) ?? null}
+              birthYear={birthYear}
+              biologicalSex={biologicalSex}
+            />
           </div>
-          {day.fitness_age && <p className="text-xs text-gray-500 mt-1">Fitness age {day.fitness_age}</p>}
+          {day.fitness_age && <p className="text-xs text-gray-500 mt-1 text-center">Fitness age {day.fitness_age}</p>}
         </div>
       </div>
     </div>
@@ -637,12 +751,17 @@ export default function HealthPage() {
     queryFn: () => api.get('/health-metrics/summary').then(r => r.data),
   })
 
+  const { data: profile } = useQuery({
+    queryKey: ['profile'],
+    queryFn: () => api.get('/profile/').then(r => r.data),
+  })
+
   // Full history for snapshot navigation.
   // Key starts with ['health-metrics'] so UploadPage invalidation hits it automatically.
   const { data: allDays } = useQuery({
     queryKey: ['health-metrics', 'all'],
     queryFn: () =>
-      api.get('/health-metrics/', { params: { limit: 365 } })
+      api.get('/health-metrics/', { params: { limit: 2000 } })
         .then(r => r.data.map(d => ({ ...d, date: d10(d.date) }))),
   })
 
@@ -721,6 +840,8 @@ export default function HealthPage() {
         sleepStages={intradayData?.sleep_stages}
         activities={dayActivities}
         latestVo2max={latestVo2max}
+        birthYear={profile?.birth_year}
+        biologicalSex={profile?.biological_sex}
         onOlder={goOlder}
         onNewer={goNewer}
         hasOlder={selectedIdx >= 0 && selectedIdx < allDaysSorted.length - 1}
@@ -857,6 +978,7 @@ export default function HealthPage() {
                 <h3 className="text-sm font-medium text-gray-300 mb-3">VO2 Max</h3>
                 <MetricChart data={metrics} dataKey="vo2max" color="#3b82f6"
                   formatter={v => v.toFixed(1)}
+                  connectNulls showDots
                   selectedDate={selDateForCharts} onDayClick={handleDayClick} />
               </div>
             )}
diff --git a/frontend/src/pages/ProfilePage.jsx b/frontend/src/pages/ProfilePage.jsx
index a8f1c8d..9d24aa4 100644
--- a/frontend/src/pages/ProfilePage.jsx
+++ b/frontend/src/pages/ProfilePage.jsx
@@ -74,7 +74,7 @@ export default function ProfilePage() {
   }, [recentMetrics])
 
   // HR / measurements form
-  const [hrForm, setHrForm] = useState({ max_heart_rate: '', birth_year: '', height_cm: '' })
+  const [hrForm, setHrForm] = useState({ max_heart_rate: '', birth_year: '', height_cm: '', biological_sex: '' })
   const [hrSaved, setHrSaved] = useState(false)
   const [hrZoneRecalc, setHrZoneRecalc] = useState(false)
   const maxHrChangedRef = useRef(false)
@@ -83,6 +83,7 @@ export default function ProfilePage() {
       max_heart_rate: profile.max_heart_rate || '',
       birth_year: profile.birth_year || '',
       height_cm: profile.height_cm || '',
+      biological_sex: profile.biological_sex || '',
     })
   }, [profile])
 
@@ -246,6 +247,21 @@ export default function ProfilePage() {
             <Input type="number" value={hrForm.height_cm} placeholder="e.g. 178" min={50} max={300}
               onChange={e => setHrForm(f => ({ ...f, height_cm: e.target.value }))} />
           </Field>
+          <Field label="Biological sex" hint="Used for VO2 max fitness category thresholds">
+            <div className="flex gap-2">
+              {['male', 'female'].map(s => (
+                <button key={s} type="button"
+                  onClick={() => setHrForm(f => ({ ...f, biological_sex: f.biological_sex === s ? '' : s }))}
+                  className={`flex-1 py-2 rounded-lg text-sm border transition-colors capitalize ${
+                    hrForm.biological_sex === s
+                      ? 'bg-blue-600 border-blue-600 text-white'
+                      : 'border-gray-700 text-gray-400 hover:text-white'
+                  }`}>
+                  {s}
+                </button>
+              ))}
+            </div>
+          </Field>
         </div>
 
         {(avgRestingHr || healthSummary?.latest?.weight_kg) && (
@@ -268,7 +284,7 @@ export default function ProfilePage() {
         <SaveButton
           onClick={() => {
             const data = Object.fromEntries(
-              Object.entries(hrForm).filter(([,v]) => v !== '').map(([k,v]) => [k, parseFloat(v)])
+              Object.entries(hrForm).filter(([,v]) => v !== '').map(([k,v]) => [k, k === 'biological_sex' ? v : parseFloat(v)])
             )
             maxHrChangedRef.current = data.max_heart_rate !== undefined && data.max_heart_rate !== profile?.max_heart_rate
             updateProfile.mutate(data)