Pre‐fatiguing Isometric Quadriceps Exercise Impairs Contralateral Quadriceps W’ During All‐out and Not Target Torque Time to Task Failure Exercise

Abstract

PurposeA crossover effect of pre‐fatiguing dynamic quadriceps contractions, between contralateral legs, was recently documented, evidencing a centrally mediated negative impact on performance, assessed by time to task failure (TTF) at a target intensity. This has since been reproduced, however, whether a crossover effect exists during isometric exercise, which permits exercise in a restricted space for a more intricate assessment of muscle function, for example, by magnetic resonance imaging (MRI), has not been determined. Therefore, this study interrogated the crossover effect of isometric pre‐fatiguing quadriceps exercise with the hypothesis that a crossover would impair TTF during isometric exercise.MethodsEight healthy participants (5M/3F) performed all‐out isometric exercise tests (60 maximal voluntary contractions, 3 s contraction, 2 s relaxation) to determine the impulse above end test torque (W′) and critical torque (CT) to establish a target torque that invoked a TTF between 8‐15 min, as defined by the torque‐duration relationship (TTF = W’/(target torque – CT)). Once established, target torque TTF and all‐out exercise CT and W’ were measured with and without pre‐fatiguing all‐out quadriceps exercise in the contralateral leg to assess the crossover effect.ResultsTTF averaged 9.8 ± 0.4 min and, interestingly, was not altered by pre‐fatigue in the contralateral leg (11.9 ± 1.0 min, p = 0.34). CT was not different in control vs. pre‐fatigue (73 ± 8 vs. 76 ± 10 N*m, p= 0.34) but W′, an indicator of exercise capacity, was reduced by 25% (6200 ± 1200 vs. 4700 ± 900 N*m*s, p = 0.02).ConclusionsThese data document a crossover effect of pre‐fatiguing isometric quadriceps exercise on subsequent contralateral quadriceps isometric exercise, but only during all‐out exercise and not target torque TTF. Furthermore, as a consequence of the unique experimental approach, utilizing a dual‐leg isometric ergometer designed to fit in a MRI, the negative impact of contralateral limb pre‐fatigue (e.g. increased afferent feedback) on W′ has been documented for the first time.