RESUMO
Ultrasound imaging was used to investigate vastus medialis (VM) architecture in 10 males and 10 females at different knee angles. Increase in muscle thickness occurs predominantly when the knee angle is changed from 0° (full extension) and 45° (p < 0.05); increases in VM pennation angle can be predominantly observed between 45° and 90° (p < 0.05). Sex differences in the VM architecture can be observed in the distal (p < 0.01) but not in the proximal region of the muscle (p > 0.11).
Assuntos
Articulação do Joelho/anatomia & histologia , Músculo Quadríceps/anatomia & histologia , Adulto , Fenômenos Biomecânicos , Feminino , Humanos , Articulação do Joelho/diagnóstico por imagem , Masculino , Pessoa de Meia-Idade , Músculo Quadríceps/diagnóstico por imagem , Amplitude de Movimento Articular , Fatores Sexuais , Ultrassonografia , Adulto JovemRESUMO
KEY POINTS: The oxygen cost of breathing represents a significant fraction of total oxygen uptake during intense exercise. At a given ventilation, women have a greater work of breathing compared with men, and because work is linearly related to oxygen uptake we hypothesized that their oxygen cost of breathing would also be greater. For a given ventilation, women had a greater absolute oxygen cost of breathing, and this represented a greater fraction of total oxygen uptake. Regardless of sex, those who developed expiratory flow limitation had a greater oxygen cost of breathing at maximal exercise. The greater oxygen cost of breathing in women indicates that a greater fraction of total oxygen uptake (and possibly cardiac output) is directed to the respiratory muscles, which may influence blood flow distribution during exercise. ABSTRACT: We compared the oxygen cost of breathing (VÌO2 RM ) in healthy men and women over a wide range of exercise ventilations (VÌE). Eighteen subjects (nine women) completed 4 days of testing. First, a step-wise maximal cycle exercise test was completed for the assessment of spontaneous breathing patterns. Next, subjects were familiarized with the voluntary hyperpnoea protocol used to estimate VÌO2 RM . During the final two visits, subjects mimicked multiple times (four to six) the breathing patterns associated with five or six different exercise stages. Each trial lasted 5 min, and on-line pressure-volume and flow-volume loops were superimposed on target loops obtained during exercise to replicate the work of breathing accurately. At â¼55 l min(-1) VÌE, VÌO2 RM was significantly greater in women. At maximal ventilation, the absolute VÌO2 RM was not different (P > 0.05) between the sexes, but represented a significantly greater fraction of whole-body VÌO2 in women (13.8 ± 1.5 vs. 9.4 ± 1.1% VÌO2). During heavy exercise at 92 and 100% VÌO2max, the unit cost of VÌE was +0.7 and +1.1 ml O2 l(-1) greater in women (P < 0.05). At VÌO2max, men and women who developed expiratory flow limitation had a significantly greater VÌO2 RM than those who did not (435 ± 44 vs. 331 ± 30 ml O2 min(-1) ). In conclusion, women have a greater VÌO2 RM for a given VÌE, and this represents a greater fraction of whole-body VÌO2. The greater VÌO2 RM in women may have implications for the integrated physiological response to exercise.