Biomechanical determinants of oxygen extraction during cross-country skiing.

To determine the relationship of muscle activation, force production, and cycle characteristics to O(2) extraction during high- and lower-intensity double poling (DP), nine well-trained male cross-country skiers performed DP on a treadmill for 3 min at 90% VO(2peak) followed by 6 min at 70%. During the final minute at each workload, arterial, femoral, and subclavian venous blood were collected for determination of partial pressure of O(2), partial pressure of CO(2), pH, and lactate. Electromyography (EMG) was recorded from six upper and lower body muscles, leg and pole forces were measured, and cardiorespiratory variables were monitored continuously. O(2) extraction was associated with time point of peak pole force (PF(peak)), duration of recovery, EMG activity, and lower body use. Arm O(2) extraction was lower than in the legs at both intensities (P < 0.001) and was reduced to a lesser extent upon decreasing the workload (P < 0.05). Arm root-mean-square EMG was higher during the poling phase and entire cycle compared with the legs (P < 0.001). Blood lactate was higher in the subclavian than in femoral vein and artery (P < 0.001) and independent of intensity. O(2) extraction was correlated to low muscle activation, later PF(peak) , prolonged poling time, and extensive dynamic lower body use. Cycle rate and recovery time were associated with O(2) extraction during high-intensity exercise only.