PowerCranks versus Normal bicycle cranks: An EMG comparison
Nuckles, J., Bills, B., Wagner, D., and Bressel, E., HPER Department, Utah State University
Powercranks are an independent bicycle crank system that eliminates contralateral leg contribution during the pulling phase of the crank cycle. As such, Powercranks are thought to activate and thus train the hip and knee muscle flexors to a greater extent then pedalling with normal cranks. Our study examined if the hip and knee flexors were in fact more active during pedalling with Powercranks than normal cranks. Eight participants randomly performed 5 min exercise bouts using Powercranks and normal cranks while surface EMG activity of muscles iliopsoas, rectus femoris, biceps femoris, and lateral gastrocnemius were recorded during stationary ergometry. EMG data were collected 1 week after cessation of a 6 week Powercrank training program. Raw EMG data for each muscle were analyzed by first computing the average root mean square (RMS) for ten crank cycles and then normalizing the mean RMS value to the peak RMS value for each muscle. Results revealed that muscles iliopsoas and rectus femoris were 31% and 35% more activity, respectively, during the Powercrank than normal crank condition (p = 0.001-0.017). Muscles biceps femoris and lateral gastrocnemius were not different between conditions (p > 0.05). From these results it may be concluded that after familiarization, pedalling with Powercranks requires greater muscle activation from hip flexor but not knee flexor muscles suggesting that pedalling with Powercranks may be a more effective exercise for the hip flexor muscles than pedalling with normal cranks.
Oral presentation at Southwest regional meeting of the American College of Sports Medicine (SWACSM) in San Diego, CA on Nov. 9, 2007. unpublished.
COMMENT: While we are not surprised by the large improvement seen in the ilipsoas muscles we are a little surprised at the lack of change seen in the hamstring and "increase" seen in the quad (rectus femoris) muscles (we would "expect" to see an increase in hamstring activation and a lessening of the quads (unless the power is substantially increased) of the quads. This "unexpected result" can be explained in many ways (including that the study participants may have already been doing a good job of applying force across the bottom of the stroke so that increases in knee flexor activity might have been too small to see). The devil is in the details, which we don't have.