The respiratory muscles may fatigue during prolonged exercises and thereby become a factor that limits extreme physical activity. The aim of the current study was to determine whether respiratory muscle fatigue imposes a limitation on extreme physical activity of well-trained young men. Electromyography (EMG) signals of respiratory (external intercostal and sternomastoid) and calf muscles (gastrocnemius) were measured (N = 8) during 1 hr of treadmill marching at a speed of 8 km/hr with and without a 15 kg backpack. The root mean square (RMS) and the mean power frequency of the EMG signals were evaluated for calculating fatigue indices. The EMG RMS revealed that the respiratory and calf muscles did not fatigue during the marching without a backpack load. The study did show, however, a significant rise in the EMG values when a backpack was carried with respect to the no-load condition (p < .05), which suggests that respiratory muscles should be trained in military recruits who are required to carry loaded backpacks while marching.
Yaara Nadiv, Ricki Vachbroit, Amit Gefen, David Elad, and Uri Zaretsky are with the Department of Biomedical Engineering, Faculty of Engineering, Tel Aviv University, Israel. Dani Moran is with Heller Institute’s Physiology Unit, Sheba Medical Center. Pinchas Halpern is with the Department of Emergency Medicine, Tel Aviv Medical Center, Israel. Anat Ratnovsky (Corresponding Author) is with the Department of Medical Engineering, Afeka College of Engineering, Tel Aviv, Israel. The first-listed coauthors Yaara Nadiv and Ricki Vachbroit contributed equally to this work.