Metabolic and circulatory responses to an isokinetic protocol

The metabolic demand and the cardiorespiratory responses to isokinetic rehabilitation protocol have been studied in 11 females (F) and 11 males (M; age: 25-30 years). The exercise consisted in 3 series of 5 maximal concentric knee extensions/flexions at 180, 120, 90, 120, 180°/s, with a 40 s pause between each series (total duration about 15 min). The work (extensors plus flexors) was determined; V̇E and V̇O2 were measured on a breath-by-breath basis. HR was continuously recorded and arterial pressure (AP) was measured during each pause. It resulted that: i) the work at 180°/s was 1170±400 J (mean±SD) in F and 1670±350 J in M, then changing according to the angular velocities (mean increase at 90°/s: 18% in F and 34% in M); ii) V̇O2, V̇E and HR increased in an exponential-like fashion, reaching constant values after about 2.5-3.5 min of exercise. V̇O2 was 0.8±0.2 L/min and 1.3±0.3 L/min, V̇E 30±6 L/min and 45±15 L/min and HR 153±13 b/min and 145±15 b/min in F and M, respectively; iii) systolic AP increased of about 20 mmHg for the entire exercise, while diastolic pressure was unchanged. Even if the exercise was intermittent, metabolic and cardiocirculatory steady states were reached, which indicate that the maximal isokinetic protocol of this study is comparable to a dynamic exercise of medium-high intensity.