INTRODUCTION: Since double-poling in cross-country skiing requires significant power during the poling motion, muscle endurance and high muscle power are essential. The upper body may rely more on muscle power and endurance than the lower body, where endurance is more critical [1]. It is known that there is a threshold in muscle activity, EMGT (electromyographic threshold), during incremental exercise [2]. Two break points (EMGT1 and EMGT2) are recognized for EMGT [3]. However, there are no reports on whether EMGT of muscles for double-poling is detected in the progressive test. This study investigates whether EMGT is observed in muscles for double poling in the progressive exercise test and, if so, how it is related to other physiological parameters. METHODS: We conducted a double-poling test using roller skis (classical type, Marwe) on a treadmill with one World Cup-level cross-country skier. During the test, surface electromyography (EMG) was recorded for three upper body muscles (triceps brachii, posterior deltoid, latissimus dorsi) and two lower body muscles (vastus lateralis, gastrocnemius). Respiratory gas exchange parameters were also measured, while blood lactate concentration was only measured before and after the test. The exercise protocol involved maintaining a constant speed of 10 km/h while increasing the incline by 1° (approximately 1.75%) every minute, starting from 1°. EMGs were expressed as moving averages every 1000 msec after rectification. The thresholds were determined through visual inspection. RESULTS/DISCUSSION: The exercise duration of the double-poling test was 8.5 minutes. An evaluation of the changes in the EMG revealed EMGT1 and EMGT2 in all muscle groups except the gastrocnemius muscle (Fig. 1). For the triceps brachii, a breakpoint corresponding to EMGT1 was observed at 6 minutes (7° incline, approximately 12.3%), and another corresponding to EMGT2 was observed at 8 minutes (9° incline, approximately 15.8%). Although slight breakpoints were observed in the respiratory gas exchange parameters, especially in ventilation and carbon dioxide output, they were not necessarily distinct. CONCLUSION: The incremental exercise test using roller skiing double-poling clearly revealed the presence of EMGT1 and EMGT2, which were less related to changes in expiratory gas variables.
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