PURPOSE: To determine the effects of six different crank lengths (150, 165, 170, 172.5, 175, and 180 mm) on gross efficiency, maximum power, optimal pedaling rate (cadence at maximum power), and joint kinematics of the hip and knee.
METHODS: Elite level cyclists (n = 18) participated in two visits to the Cal Poly Cycling Lab. The purpose of the first lab session was to measure VO2 peak (60.6 ± 7.6 mL·min-1·kg-1), participant characteristics (28.2 ± 5.3 yrs; 175.6 ± 7.4 cm; 70.5 ± 5.3 kg; 255 ± 105 km/week), and complete familiarization trials with four different crank lengths. These practice trials consisted of 4 second seated maximal sprints on the participant’s original crank length (170, 172.5, or 175 mm) and three other crank lengths (150, 165, and 180 mm). The second test session was a single-blind randomized crossover design with the six different crank lengths. After a 5 minute warm up, participants performed a 3 minute steady state effort at 65% VO2 peak and 90 rpm. This was followed by two maximum effort 4 second seated sprints with 90 seconds rest prior to each sprint. Participants rested for 5 minutes before the next crank length trial.
RESULTS: During steady state cycling, shorter cranks had a higher gross efficiency (150 mm: 22.1%) compared to longer cranks (180 mm: 21.6%), (p < 0.001). No significant differences were found between crank lengths for maximum power output during the 4 second sprints. There was an increase in optimal pedaling rate between 150 mm cranks (130 rpm) and all other lengths (180 mm: 120 rpm) (p < 0.001). 150 mm cranks have a significantly smaller hip (45°) and knee (67°) range of motion than all other cranks measured (180 mm: hip 51°, knee 75°) (p < 0.001).
CONCLUSIONS: Shorter cranks resulted in a significantly higher gross efficiency, smaller knee and hip range of motion, and a higher optimal pedaling rate.