A Comparison of Measures of the Bilateral Limb Deficit During Short and Long Time Isometric Knee Extensions

Aim: To investigate the presence of the Bilateral Limb Deficit (BLD) during isometric knee extensions and the differences in voluntary activation and muscle fatigue during bilateral and unilateral contractions. Methods: Twelve subjects (6 female, 6 male, (mean ± standard deviation) age = 27.6 ± 6.9 years) completed a series of short (5-second) and long (30-second) isometric knee extensions during which force, myoelectric signal (MES) amplitude and voluntary activation were measured.Results: No BLD was detected during the isometric contractions and voluntary activation (estimated using the twitch interpolation technique) did not differ between unilateral and bilateral conditions The mean voluntary activation levels were significantly higher (p<.05) during the short (5-second) contractions (91% activation) than the first five seconds of the long (30-second) contractions (80% activation). Unilateral and bilateral contractions resulted in similar decreases in fatigue (measured as a decline in mean frequency). Significant differences were detected in the mean frequency (14 – 17 Hz) between short and long contractions (p < 0.001). Finally, it was found that the current used to elicit the maximal twitch force differed between unilateral and bilateral contractions suggesting that there are differences in the twitch response that may contribute to the BLD.Conclusion: These data showed that the BLD is not present during isometric knee extensions and that voluntary activation and neuromuscular fatigue are similar for bilateral and unilateral conditions. Differences were detected in voluntary activation between short and long contractions and between the current required to elicit a supramaximal twitch during bilateral and unilateral contractions.