Cardiorespiratory and metabolic determinants during moderate and high resistance exercise intensities until exhaustion using dynamic leg press: comparison with critical load

The objective of this study was to assess cardiovascular, respiratory, and metabolic responses during a commonly used dynamic leg press resistance exercise until exhaustion (T(Ex)) at different intensities and compare with critical load (CL). This was a prospective, cross-sectional, controlled, and crossover study. Twelve healthy young men (23±2.5 years old) participated. The subjects carried out three bouts of resistance exercise in different percentages of 1 repetition maximum (60, 75, and 90% 1RM) until T(Ex). CL was obtained by means of hyperbolic model and linearization of the load-duration function. During all bout intensities, oxygen uptake (VO(2)), carbon dioxide production (VCO(2)), ventilation (V(E)), and respiratory exchange ratio (RER) were obtained. Variations (peak-rest=Δ) were corrected by T(Ex). In addition, systolic and diastolic blood pressure (SBP and DBP), blood lactate concentration [La-] and Borg scores were obtained at the peak and corrected to T(Ex). CL induced greater T(Ex) as well as number of repetitions when compared to all intensities (P<0.001). During CL, Borg/T(Ex), ΔSBP/T(Ex), ΔDBP/T(Ex), and [La-] were significantly lower compared with 90% load (P<0.0001). In addition, VO(2,) VCO(2,) V(E), and RER were higher during CL when compared to 90 or 75%. T(Ex) was significantly correlated with VO(2) on CL (r=0.73, P<0.05). These findings support the theory that CL constitutes the intensity that can be maintained for a very long time, provoking greater metabolic and ventilatory demand and lower cardiovascular and fatigue symptoms during resistance exercise.