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Eur J Appl Physiol. 2013 Sep;113(9):2391-9. doi: 10.1007/s00421-013-2675-y. Epub 2013 Jun 15.

Effects of neuromuscular fatigue on the electromechanical delay of the leg extensors and flexors in young and old men.

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Applied Musculoskeletal and Human Physiology Laboratory, Department of Health and Human Performance, Oklahoma State University, Stillwater, OK 74078, USA.



The purpose of this study was to investigate the effects of a fatigue-inducing bout of submaximal, intermittent isometric contractions on the electromechanical delay (EMD) of the leg extensors and flexors in young and old men.


Twenty young (mean ± SD: age = 25 ± 2.8 years) and sixteen old (age = 70.8 ± 3.8) recreationally active men performed maximal voluntary contractions (MVCs) followed by a fatigue-inducing protocol consisting of intermittent isometric contractions of the leg extensors or flexors using a 0.6 duty cycle (6 s contraction, 4 s relaxation) at 60 % of MVC until volitional fatigue. MVCs were again performed at 0, 7, 15, and 30 min post fatigue. A three-way mixed factorial ANOVA was used to analyze the EMD data.


There was a two-way muscle × time interaction (P = 0.039) where the EMD of the leg flexors was greater (P = 0.001-0.034) compared with baseline at all post fatigue time periods, but was only greater at immediately post fatigue for the extensors (P = 0.001). A significant two-way interaction for muscle × age (P = 0.009) revealed that the EMD was greater (P = 0.003) for the extensors for the old compared with the young men, but not different for the flexors (P = 0.506).


These findings showed differential fatigue-induced EMD recovery patterns between the leg extensors and flexors with the flexors being slower to recover and also that age-related increases of EMD are muscle group specific. The sustained increased EMD of the flexors during recovery may have important injury and performance implications in a variety of populations and settings.

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