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

Poster Board Number: E347

Matthew Lewis (University of Utah), Ryan Broxterman (University of Utah), Jesse Craig (University of Utah), Joshua Weavil (University of Utah), Fabio Laginestra (University of Verona), Catherine Jarrett (University of Utah), Kanokwan Bunsawat (University of Utah), Markus Amann (University of Utah), Russell Richardson (University of Utah)

Purpose: A 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.

Methods: Eight 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.

Results: TTF 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).

Conclusions: These 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.

This study was supported by National Heart, Lung, and Blood Institute Grants (HL-103786, HL-116579, HL142603, HL-125756, and HL-091830); a Ruth L. Kirschstein National Research Service Award T32 (HL 139451); Merit (I01 CX001999, E6910-R, E1697-R, E1572-P, and E3207-R), Spire (I21RX001572, E1433-P), Advanced Fellowship in Geriatrics and Senior Research Career Scientist (E9275-L) Awards from the Veterans Affairs Rehabilitation Research and Development.