Source
1Canadian Centre for Activity and Aging, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, ON, Canada; 2School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, NL, Canada; 3Departments of Clinical Neurological Sciences and Rehabilitation Medicine, The University of Western Ontario, London, ON, Canada; 4School of Physical Therapy, Faculty of Health Sciences, The University of Western Ontario, London, ON, Canada; 5Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, ON, Canada.
Abstract
A contributing factor to the loss of muscle mass and strength with adultaging is the reduction in the number of functioning motor units (MUs). Recently, we reportedthat life-long competitive runners (masters runners; ∼66y) had greater numbers of MUs in a leg muscle (tibialis anterior) than age-matched recreationally active controls. This suggested that chronic exposure to high levels of physical activity may limit the loss of MU numbers with adultaging. However, it is unknown if this finding is the result of chronic activation of the specificallyexercised motoneuron (MN) pool (i.e., tibialis anterior), or an overall systemic neuroprotective effect of high levels of physical activity.
PURPOSE:
The purposewas to estimate the number of functioning MUs (MUNEs) in the bicepsbrachii (an upper body muscle not directly loaded by running) of 9 young (27±5y) and 9 old (70±5y) men, and 9 life-long competitive masters runners (67±4y).
METHODS:
Decomposition-enhanced spike-triggered averagingwas used to measure surface and intramuscular electromyography signals during elbow flexion at 10% of maximum voluntary isometric contraction.
RESULTS:
Derived MUNEswerelower in the biceps of runners (185±69 MUs) and old men (133±69 MUs)thanthe young (354±113 MUs), but the old and masters runners were similar.
CONCLUSION:
Althoughthere were no significant differences in MUNE between both older groups in the biceps brachii muscle, with the number of subjects tested here, we cannot eliminate the possibility of some whole body neuroprotective effect. However, when compared with the remote biceps muscle a greater influence on age-related spinal MN survival was found in a chronically activated MN pool specific to the exercised muscle.