Novel Crank with Elastomer Spring Improves Effective Power in Trained Cyclists and Triathletes

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PURPOSE: Test claims a novel cycling crank (IMPACT, Huron Cycling, LLC) may increase effective cycling power. The crank incorporates an elastomer spring is purported to return energy during the “dead spot” of the pedal revolution, thus improving the net transfer of external power. METHODS: 15 trained cyclists/triathletes (38 ± 7 y, 74.5 ± 9.9 kg, 174.7 ± 6.6 cm) consented to procedures approved by the EMU-HSRC. The study consisted of three visits. During V1, subjects performed a graded exercise protocol on a Velotron (Racermate, WA) cycle ergometer (VCE) to determine ventilatory threshold (VT) (Parvomedics, CO) and power at VT (pVT).During V2 and V3, subjects warmed-up on VCE then completed twelve, six-minute stages which consisted of pedaling at a 85 rpm while maintaining a power output equivalent to 70, 80, or 90 % of pVT. Additionally, a cadence effect was tested at 80% pVT at 75, 85 or 95 rpm. The six stages were randomized, and each stage was completed twice; i) with a pin in the crank (CON), and ii) without the pin (EXP). The pin eliminated the spring effect of the elastomer, thus making a traditional rigid crank. There was a minute rest between each stage, except when changing from EXP to CON (3 minutes) to change the pin and allow subject to drink. The VCE was used as the external load generator and power was also measured at the pedals (PowerTap P1, WI; PT) to determine if any difference in power between external load and power necessary to turn the cranks against the load was present. MANOVA statistical tests compared %pVT between PT and VCE and VO2 in both EXP and CON (α=.05). RESULTS: Across all conditions, there was a Large effect for EXP power being 1.3 % lower than CON (p=.008; n=.028 ). Although not significant, there were small effects for cadence at 80% pVT, where EXP was lower than CON, but to a greater extent at 85 and 95 than 75 rpm (77.7+ 2.8, 77.1+3.6 and 78.5+4.2 %, respectively, n=.019). There was no significant difference between VO2 at each workload when expressed as a percentage of VT between EXP and CON. There were no significant differences by trial for any variables tested. CONCLUSION: Lower power, but similar VO2 during EXP compared to CON supports the notion that the IMPACT crank improves effective power during cycling. Although small in magnitude, the effect was large and could be of interest to competitive cyclists or triathletes.