Changing crank length by ±5 mm does not change gross efficiency or heart rate; a longer crank adds 1.8–3.4° of hip and knee flexion and range of motion
Key Findings
Gross efficiency was 20.4%, 20.1% and 20.3% on the preferred, +5 mm and −5 mm cranks, with heart rate unchanged; the longer crank added 1.8–3.4° of hip and knee flexion.
Twelve amateur road cyclists rode their preferred crank (172.5–175 mm), +5 mm and −5 mm at 150, 200 and 250 W and 91.3 ± 0.8 rpm.
Heart rate 144 ± 13, 145 ± 12 and 145 ± 13 bpm; gross efficiency 20.4 ± 2.1, 20.1 ± 2.2 and 20.3 ± 2.4% — no significant effect.
With the longer crank, maximum flexion and range of motion of the hip and knee increased by 1.8–3.4° (P < 0.05); the ankle was unaffected.
Authors: in case of doubt between two lengths, the shorter one might be recommended.
Practical Application
What a crank change actually changes is how far the hip and knee fold at the top of the stroke. That is the reason to go shorter: a closed hip in an aero or low position, tightness or pinching at the top, a knee or hip that complains.
When undecided between two lengths, the shorter is the reasonable default — on joint-angle grounds, since efficiency is the same.
Do not promise more power, better climbing or injury prevention from a crank change: none of these was measured.
Limitations
Acute, N = 12; the authors' remark about long-term adverse effects of longer cranks is speculation — no pain or injury outcome was measured.
A submaximal joint-mechanics study (Barratt 2016, DOI 10.1249/mss.0000000000000817) found knee extension moments tended to decrease with longer cranks: "shorter cranks unload the knee" is not supported.
Abstract only was read.