diff --git a/exercises.py b/exercises.py
new file mode 100644
index 0000000..d277ce8
--- /dev/null
+++ b/exercises.py
@@ -0,0 +1,184 @@
+import time
+import numpy as np
+
+# COCO keypoint indices used by YOLO pose
+_NOSE        =  0
+_L_SHOULDER  =  5
+_R_SHOULDER  =  6
+_L_ELBOW     =  7
+_R_ELBOW     =  8
+_L_WRIST     =  9
+_R_WRIST     = 10
+_L_HIP       = 11
+_R_HIP       = 12
+_L_ANKLE     = 15
+_R_ANKLE     = 16
+
+
+# ── helpers ──────────────────────────────────────────────────────────────────
+
+def _angle(a, b, c):
+    a, b, c = np.array(a), np.array(b), np.array(c)
+    rad = np.arctan2(c[1]-b[1], c[0]-b[0]) - np.arctan2(a[1]-b[1], a[0]-b[0])
+    deg = np.abs(rad * 180.0 / np.pi)
+    return 360 - deg if deg > 180 else deg
+
+
+def _elbow(kps, conf, side):
+    sh, el, wr = (_L_SHOULDER, _L_ELBOW, _L_WRIST) if side == 'left' \
+                 else (_R_SHOULDER, _R_ELBOW, _R_WRIST)
+    return _angle(kps[sh], kps[el], kps[wr]), min(conf[sh], conf[el], conf[wr])
+
+
+def _best_elbow(kps, conf):
+    la, lv = _elbow(kps, conf, 'left')
+    ra, rv = _elbow(kps, conf, 'right')
+    if lv > 0.5 and rv > 0.5:
+        return (la + ra) / 2, max(lv, rv)
+    return (la, lv) if lv >= rv else (ra, rv)
+
+
+def _mid(kps, a, b):
+    return ((kps[a][0] + kps[b][0]) / 2,
+            (kps[a][1] + kps[b][1]) / 2)
+
+
+def _is_horizontal(kps):
+    """Nose and hips at similar y → body is lying flat (side-on view)."""
+    nose_y     = kps[_NOSE][1]
+    _, hip_y   = _mid(kps, _L_HIP, _R_HIP)
+    return abs(nose_y - hip_y) < 0.38
+
+
+def _wrists_above_shoulders(kps, margin=0.05):
+    """At least one wrist clearly above its shoulder (front-on view)."""
+    l = kps[_L_WRIST][1] < kps[_L_SHOULDER][1] - margin
+    r = kps[_R_WRIST][1] < kps[_R_SHOULDER][1] - margin
+    return l or r
+
+
+def _plank_deviation(kps):
+    """Signed hip deviation from the shoulder-to-ankle line.
+    0 = straight.  Positive = hips sagging.  Negative = hips piking."""
+    sh_x, sh_y = _mid(kps, _L_SHOULDER, _R_SHOULDER)
+    hi_x, hi_y = _mid(kps, _L_HIP,      _R_HIP)
+    an_x, an_y = _mid(kps, _L_ANKLE,    _R_ANKLE)
+    dx = an_x - sh_x
+    if abs(dx) < 0.01:
+        return 0.0
+    t = (hi_x - sh_x) / dx
+    return hi_y - (sh_y + t * (an_y - sh_y))
+
+
+# ── exercise update functions ─────────────────────────────────────────────────
+# All return (new_stage: str | None, rep_counted: bool)
+# Side-on:  push-up, curl, sit-up, plank
+# Front-on: pull-up, bench
+
+def update_pushup(kps, conf, stage):
+    angle, vis = _best_elbow(kps, conf)
+    if vis < 0.4 or not _is_horizontal(kps):
+        return stage, False
+    if angle > 155 and stage != 'up':
+        return 'up', False
+    if angle < 85 and stage == 'up':
+        return 'down', True
+    return stage, False
+
+
+def update_pullup(kps, conf, stage):
+    angle, vis = _best_elbow(kps, conf)
+    if vis < 0.4 or not _wrists_above_shoulders(kps):
+        return stage, False
+    if angle > 155 and stage != 'down':
+        return 'down', False
+    if angle < 90 and stage == 'down':
+        return 'up', True
+    return stage, False
+
+
+def update_bench(kps, conf, stage):
+    """Horizontal body + wrists above shoulders (lying on back). Count on lockout."""
+    angle, vis = _best_elbow(kps, conf)
+    if vis < 0.4 or not _is_horizontal(kps) or not _wrists_above_shoulders(kps):
+        return stage, False
+    if angle < 90 and stage != 'down':
+        return 'down', False
+    if angle > 155 and stage == 'down':
+        return 'up', True
+    return stage, False
+
+
+def update_curl(kps, conf, stage):
+    """Standing (not horizontal). Count at full curl."""
+    angle, vis = _best_elbow(kps, conf)
+    if vis < 0.4 or _is_horizontal(kps):
+        return stage, False
+    if angle > 150 and stage != 'down':
+        return 'down', False
+    if angle < 60 and stage == 'down':
+        return 'up', True
+    return stage, False
+
+
+def update_situp(kps, conf, stage):
+    """Side-on view. Count when shoulders rise well above hips."""
+    _, sh_y = _mid(kps, _L_SHOULDER, _R_SHOULDER)
+    _, hi_y = _mid(kps, _L_HIP,      _R_HIP)
+    rise = hi_y - sh_y      # larger = shoulders further above hips
+    if rise < 0.10 and stage != 'down':
+        return 'down', False
+    if rise > 0.28 and stage == 'down':
+        return 'up', True
+    return stage, False
+
+
+class _PlankUpdater:
+    """Holds a per-second tick timer so the count increments in whole seconds."""
+    _LIMIT = 0.08
+
+    def __init__(self):
+        self._tick = None
+
+    def __call__(self, kps, conf, stage):
+        if stage is None:
+            self._tick = None
+
+        dev  = _plank_deviation(kps)
+        flat = _is_horizontal(kps)
+
+        if not flat:
+            self._tick = None
+            return 'get flat', False
+        if dev > self._LIMIT:
+            self._tick = None
+            return 'sagging', False
+        if dev < -self._LIMIT:
+            self._tick = None
+            return 'piking', False
+
+        now = time.time()
+        if self._tick is None:
+            self._tick = now
+        if now - self._tick >= 1.0:
+            self._tick = now
+            return 'holding', True
+        return 'holding', False
+
+
+_plank_fn = _PlankUpdater()
+
+def update_plank(kps, conf, stage):
+    return _plank_fn(kps, conf, stage)
+
+
+# ── registry ──────────────────────────────────────────────────────────────────
+
+EXERCISES = {
+    'p': {'name': 'PUSH-UPS',    'fn': update_pushup, 'color': (50,  220, 100), 'unit': 'REPS'},
+    'u': {'name': 'PULL-UPS',    'fn': update_pullup, 'color': (80,  120, 255), 'unit': 'REPS'},
+    'b': {'name': 'BENCH PRESS', 'fn': update_bench,  'color': (0,   200, 255), 'unit': 'REPS'},
+    'c': {'name': 'BICEP CURLS', 'fn': update_curl,   'color': (200,  80, 255), 'unit': 'REPS'},
+    's': {'name': 'SIT-UPS',     'fn': update_situp,  'color': (255, 160,  30), 'unit': 'REPS'},
+    'l': {'name': 'PLANK',       'fn': update_plank,  'color': (30,  200, 220), 'unit': 'SECS'},
+}