Worked example & answer key · PE · Year 9
DCF: Citizenship → Health and well-being
Also assessed, LNF: Numeracy → Learning that statistics represent data and that probability models chance helps us make informed inferences and decisions → Interpreting data
An annotated Year 9 model response and complete answer key. Key figures: Step 1 heart-rate errors 12, 11, 2, 15, 2, 12 bpm (total 54 bpm, overall mean 9 bpm; sprint mean 12.5 bpm vs steady run mean 2 bpm); recovery rates 24, 25, 22, 26, 20, 26 bpm/min. Step 2 GPS distance errors 8 m (8%), 18 m (9%), 24 m (6%), 20 m (1%).
(a) Completed heart-rate and recovery table
| Session | Type | Chest-strap peak (bpm) | Wrist peak (bpm) | Error: Chest − Wrist (bpm) | 2-min recovery HR (bpm) | Recovery rate per min: (Peak − Rec) ÷ 2 |
|---|---|---|---|---|---|---|
| 1 | Short sprint | 184 | 172 | 12 | 136 | (184 − 136) ÷ 2 = 24 bpm/min |
| 2 | Short sprint | 188 | 177 | 11 | 138 | (188 − 138) ÷ 2 = 25 bpm/min |
| 3 | Steady run | 170 | 168 | 2 | 126 | (170 − 126) ÷ 2 = 22 bpm/min |
| 4 | Short sprint | 192 | 177 | 15 | 140 | (192 − 140) ÷ 2 = 26 bpm/min |
| 5 | Steady run | 156 | 154 | 2 | 116 | (156 − 116) ÷ 2 = 20 bpm/min |
| 6 | Short sprint | 186 | 174 | 12 | 134 | (186 − 134) ÷ 2 = 26 bpm/min |
(b) Mean error comparison:
Total error across all 6 sessions = 12 + 11 + 2 + 15 + 2 + 12 = 54 bpm. Overall mean error = 54 ÷ 6 = 9 bpm.
Mean error on the 4 short sprint sessions (Sessions 1, 2, 4 and 6) = (12 + 11 + 15 + 12) ÷ 4 = 50 ÷ 4 = 12.5 bpm.
Mean error on the 2 steady runs (Sessions 3 and 5) = (2 + 2) ÷ 2 = 4 ÷ 2 = 2 bpm.
The wrist tracker is more than six times less accurate during sprints because violent arm swings create motion artefacts on the skin and the optical sensor lags 10 to 15 seconds behind sudden spikes in pulse.
Calculates overall and subgroup means accurately and links the numerical gap (12.5 bpm vs 2 bpm) to how optical wrist sensors work. Evidences criteria 1 and 2.
(a) Completed GPS inaccuracy table
| Run description | True distance (m) | Wrist GPS (m) | Distance error (m) | Percentage inaccuracy: (Error ÷ True) × 100 |
|---|---|---|---|---|
| 100 m straight sprint | 100 | 92 | 8 m | (8 ÷ 100) × 100 = 8% |
| 200 m bend sprint | 200 | 182 | 18 m | (18 ÷ 200) × 100 = 9% |
| 400 m one-lap sprint | 400 | 376 | 24 m | (24 ÷ 400) × 100 = 6% |
| 2,000 m straight park path | 2,000 | 1,980 | 20 m | (20 ÷ 2,000) × 100 = 1% |
(b) Explanation: Even though the 2,000 m run has a 20 m error, 20 m out of 2,000 m is only 1%. On the 200 m bend sprint, the GPS samples only once every 3 seconds and joins points with straight lines that cut inside the curve of the track, losing 18 m (9%). Nia must keep using a stopwatch and measured track lines for 100 m sprints because the GPS auto-split is 1.2 seconds too slow (14.6 s instead of 13.4 s).
Shows why percentage error matters more than raw metres when comparing short and long distances. Evidences criterion 3.
| App setting | Why this is a privacy or well-being risk | Safe setting to choose instead |
|---|---|---|
| A: Public profile (name, age 14, school, photo) | Strangers online can identify an under-18 pupil by full name, age, school uniform and location. | Set account to Private (Approve-only) so only trusted family or school athletics coaches can view logs, and remove school name and uniform photo. |
| B: Full street GPS map (14 Heol y Castell, Tue/Thu 07:15) | Reveals Nia’s exact home address and shows a predictable routine of when she leaves home alone in the morning. | Hide route maps completely, or enable a 500 m privacy zone around home and school and turn off automatic posting. |
| C: Live Location Beacon (enabled for 312 followers) | Anyone among her 312 public followers can track where she is running in real time. | Switch Live Location Beacon OFF (or share only with a parent or carer when running outdoors). |
| D: 21:30 “Streak lost!” alerts (exercising with a sore ankle) | Gamified streak badges pressure pupils into exercising late at night, disrupting sleep and worsening sports injuries. | Turn off streak and calorie alerts, set Quiet Hours after 20:00, and schedule rest and injury-recovery days. |
Links each setting to a concrete safeguarding or physical well-being consequence and gives a practical fix. Evidences criterion 4.
The PE department should use wrist fitness trackers for steady endurance runs and cross-country pacing, where the mean heart-rate error is only 2 bpm and the 2,000 m GPS distance inaccuracy is just 1%. However, wrist trackers should not be used to time or monitor short track sprints, because optical lag causes a mean heart-rate error of 12.5 bpm and GPS corner-cutting causes 8% to 9% distance error on 100 m and 200 m sprints; chest straps, trundle-wheel track marks and stopwatches should be used instead. For pupil safeguarding, school policy should ban public fitness app profiles for under-18s, require Live Location to be switched off, and enforce a 500 m privacy zone around home and school addresses. Finally, pupils should disable daily streak notifications so that rest days and injury recovery are protected.
Combines calculated evidence from Steps 1 and 2 with clear equipment, privacy and well-being rules. Evidences criterion 5.
Percentage error in Peak HR: Session 4 (Hill sprints) = (15 ÷ 192) × 100 = 7.8%. Session 5 (Easy jog) = (2 ÷ 156) × 100 = 1.3%.
100 m mean speed comparison: True speed from track and stopwatch = 100 m ÷ 13.4 s = 7.46 m/s. Wrist GPS speed = 92 m ÷ 14.6 s = 6.30 m/s (an underestimate of 1.16 m/s).