Knees Caving and Heels Lifting in the Barbell Class
A 52-year-old woman, 68 kg, has attended a community barbell class twice a week for eight weeks and now back-squats 30 kg for 3 sets of 10. Observation: in the first five reps her knees track over her feet; in reps 6-10 both knees drift medially by roughly 3-4 cm, her heels lift about 2 cm off the floor, and her trunk leans forward so the bar travels ahead of her midfoot. She reports a dull ache at the front of both knees that began three weeks ago, worse going down stairs and after class. There is no swelling, no locking and no giving way. A knee-to-wall test gives 6 cm on both sides, while her class partner reaches 12 cm. In side-lying hip abduction she can hold against gentle resistance but cannot hold 10 seconds without the pelvis dropping. She wants to keep adding 2.5 kg per week.
1. Explain the three observed faults and link each one to the load on a specific structure using moment-arm and torque reasoning.
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1. Medial knee drift (dynamic valgus). The pelvis drops on the stance side because the hip abductors fatigue across the set, so the femur adducts and internally rotates and the knee follows. In the frontal plane this greatly increases the external knee abduction moment - the perpendicular distance from the knee joint centre to the ground reaction force vector grows - and it compresses the lateral compartment while increasing the lateral pull on the patella. That is the mechanism behind her anterior knee ache and the pain on stairs, where patellofemoral joint reaction force peaks.
2. Heel lift. The knee-to-wall result (6 cm versus 12 cm) shows restricted ankle dorsiflexion. When depth exceeds available dorsiflexion, the heel lifts and the foot's base of support moves forward. To keep the bar over the midfoot the lifter must lean the trunk forward, which lengthens the horizontal distance from the bar to L5-S1 and to the hip - a larger spinal and hip extensor moment, and more shear at the lumbar segments.
3. Forward bar path. This is a consequence of 1 and 2 rather than an independent fault. The bar drifting ahead of the midfoot increases the moment arm of the load about every joint below it, so the set feels heavier exactly when her stabilisers are most fatigued.
Note the time course: the faults appear in reps 6-10. That is a fatigue and motor-control signature, not a fixed structural deformity, which matters for the intervention.
2. Rank your interventions across mobility, strength and technique, and write a 4-week progression with sets, reps and loads.
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Priority ranking.
- Technique and range - reduce the depth that produces the heel lift today, so she stops rehearsing the fault. Highest immediate payoff.
- Ankle dorsiflexion mobility - the rate-limiting constraint on depth; cheap and daily.
- Hip abductor strength and endurance - the fatigue-driven valgus will not be fixed by cueing alone, but it is the slowest to change.
Weeks 1-2. Back squat to a box set at the depth she can hold heels down, 3 x 8 at 25 kg, tempo 3-1-2, twice weekly. Temporary 2.5 cm heel wedge or plate under the heels to allow depth while dorsiflexion improves. Daily: knee-to-wall mobilisation 3 x 10 per side, calf stretch 2 x 30 s. Abductor work: side-lying abduction 2 x 12, banded lateral walks 2 x 12.
Weeks 3-4. Full squat, wedge still in place, 3 x 8 at 25-30 kg. Add split squat 2 x 8 per leg at body weight. Progress load only when reps 6-10 look like reps 1-5 - that is the actual criterion, not the calendar.
Keep her training. Pain is dull, 3/10, with no swelling or instability, so modification beats rest; a two-week deload to 25 kg costs nothing, whereas losing the habit costs the programme.
3. Choose the cues you would use and explain why, and state how you keep her safe inside a 12-person class with one instructor.
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Cue externally. The research on attentional focus favours cues directed at the movement effect rather than at muscles. Use: 'spread the floor apart with your feet', 'point your knees at your little toes', 'push the floor away', 'make your feet quiet'. Avoid 'activate your glutes' and 'squeeze your abductors' - internal cues compete for attention with the task, and she is already thinking about her knees.
Add a tactile constraint rather than more words. A light band around the knees gives instant feedback on drift with no talking, which is what a single instructor in a 12-person class can actually deliver. One demonstration, one cue per set maximum, and feedback addressed to the whole group rather than to her by name.
Class management.
- Give her the box-squat variant in the same block as everyone else; the class does not need to know why.
- Put her in the middle of the room, not the back, where you can see reps 6-10.
- One 20-second individual check per session, scheduled, not shouted across the room.
- Ask for a pain score each session; agree in advance that above 4/10 or any swelling means a referral, not another deload.