Muscle Coordination during an Outdoor Cycling Time Trial

Muscle activity in cycling has primarily been studied in the laboratory; however, conclusions are limited by the ability to recreate realistic environmental conditions. The purpose of this study was to determine muscle coordination patterns in an outdoor time trial and investigate their relationships to power output (PO), total muscle activity (Itot), overall mechanical efficiency (ηO), cadence, and gradient. Surface EMG, gradient, and cycling parameters were measured while cycling 18.8 km outdoors. A principal component analysis was used to establish coordination patterns that were compared with Itot, ηO, PO, cadence, and gradient. PO was positively correlated with Itot, and high PO was associated with elevated rectus femoris and vastus lateralis activity and synchronization of muscles crossing the same joint. PO and cadence demonstrated positive and negative relationships, respectively, with gradient. Relationships between muscle coordination, PO, ηO, Itot, and gradient showed that muscle coordination, PO, and ηO fluctuate during an outdoor time trial as a result of pacing and gradient. A trade-off existed between ηO and PO, and ηO was dependent on muscle activation around the top and bottom of the pedal cycle and activity in more than the knee extensor muscles. Fluctuations in muscle activity due to the changing PO, from pacing and terrain, seemed to mitigate fatigue indices seen in indoor cycling studies. This study provides evidence that muscle activity is dependent on the terrain aspects of the cycle course as muscle coordination changes with the altered locomotor demands. The coordination patterns significantly covaried with PO, Itot, ηO, cadence, and gradient, which highlights the importance of recording these parameters under field conditions and/or careful reproduction of outdoor environments in indoor studies.