July 8, 2016
Usha Kuruganti, Victoria Chester, Danielle Losier and Monica MacDonald
Andrew and Marjorie McCain Human Performance Laboratory, Faculty of Kinesiology, University of New Brunswick, Fredericton NB, E3B 5A3.
The bilateral limb deficit (BLD) is defined as the reduction in force production during bilateral compared to summed unilateral contractions of the same muscle group(s). The BLD has been shown in both large and small muscle groups, athletic and non-athletic populations, can be reduced with training and is more often present in dynamic contractions. The underlying mechanisms of BLD remain to be determined. One potential mechanism for the decline in force during bilateral contractions could be due to neural inhibition, however the results of research to date have been mixed. One method to investigate this is through the use of surface electrodes placed over the muscles of interest. As the muscle contracts an electrical signal can be detected at the skin’s surface, also known as electromyography (EMG). This signal reflects the neural commands sent to the muscle. Changes in the EMG pattern would provide evidence of the neural mechanisms causing the deficit. Better understanding of this phenomenon has applications in athletic training, particular in those sports requiring maximum performance of both limbs.
The purpose of this study was to examine the presence of the BLD during maximal isometric leg press and handgrip exercises in female swimmers (n=9, mean age = 20.1 ± 1.3 years) and non-athletes (n=9, mean age = 21.7 ± 1.3 years) to gain further insight into this phenomenon and its potential impact to athletic training.
Force and surface EMG measures were collected from participants under bilateral and unilateral conditions for handgrip and leg press exercises. Bilateral limb ratios (BLR) were calculated for swimmers (BLRS) and non-athletes (BLRNA). A deficit was found for swimmers and non-athletes in leg force EMG, however no BLD was detected in hand force EMG. Furthermore, no significant differences were found between groups (swimmers versus non athletes) for leg force, leg EMG, hand force, and hand EMG. In summary, a BLD was detected for both groups during bilateral isometric leg press. This suggests that while the BLD may be affected by neural inhibition, other factors such as postural stability requirements to perform the exercise may be involved.
Reference:
Applied Physiology, Nutrition, and Metabolism, 2014, 39(11): 1245-1249, 10.1139/apnm-2014-0040
This article is a summary of an article published in Applied Physiology, Nutrition & Metabolism. If you intend citing any information in this article, please consult the original article and cite that source.