Medicine & Science in Sports & Exercise:
C-35 Free Communication/Poster - Motor Units and EMG: MAY 28, 2009 7:30 AM - 12:30 PM ROOM: Hall 4F
Deschenes, Michael R. FACSM; Roby, Mackenzie A.; Glass, Emily K.
College of William & Mary, Williamsburg, VA.
(No relationships reported)
Although the effects of aging on training-induced remodeling of skeletal muscle have been well studied, little is known regarding the capacity of aging to influence exercise-induced adaptations of the neuromuscular junction (NMJ).
PURPOSE: This study aimed to determine whether aged and young adult NMJs responded differently to the same program of endurance training.
METHODS: Twenty young adult (8 mo old) and 20 aged (24 mo old) male Fischer 344 rats were randomly assigned to either exercise trained or control groups (4 groups, N=10/group). Trained rats from each age group participated in an identical 10 week program of treadmill running (5days/wk) while age matched controls remained sedentary in their cages. Following the 10 week intervention, all rats were euthanized and soleus muscles were removed and quickly frozen at resting length. Muscles were sectioned and stained with cytofluorescent techniques to visualize pre-synaptic nerve terminal branches, and post-synaptic acetylcholine receptors. Pre- and post-synaptic images were collected with confocal microscopy and used to quantify various parameters of NMJ morphology. Myofiber profiles (fiber size and composition) were determined with standard histochemistry and light microscopy. Data were analyzed with a 2 way ANOVA with main effects of age and treatment.
RESULTS: Young adult, but not aged rats demonstrated significant (P<0.05) training-induced increases in pre-synaptic nerve terminal branch number, total branch length, and branching complexity. Similarly, when examining post-synaptic morphology, only young rats displayed significant training-induced increments in perimeter length around endplate regions, and expanded areas occupied by acetylcholine receptors. And although myofibers of aged control rats were smaller than their younger counterparts, training elicited a significant increase in fiber size only among aged rats restoring their size to that observed among younger ones.
CONCLUSIONS: Our data show that aging blunts the adaptability of the NMJ to endurance exercise training. This is meaningful because failure of neuromuscular transmission is an important contributor to muscle fatigue, thus limiting exercise performance and associated health benefits.
Supported by the NIH grant R15 AG17440.