MOTOR UNIT DISCHARGE BEHAVIOR DURING 10% MVC ISOMETRIC CONTRACTIONS FOLLOWING RESISTANCE EXERCISE TRAINING IN YOUNG AND OLDER ADULTS

1. The activity of 40 triceps brachii motor units was recorded from the dominant arms of 9 healthy adult volunteers (age 27.8 +/- 4.4 yr, mean +/- SD) during a fatigue task that included both isometric and anisometric contractions. The fatigue task lasted 8.3 min and consisted of 50 extension and 50 flexion movements of the elbow. Each movement (40 degrees in 0.8s) was separated by an isometric contraction. A constant load resisting extension of 17.7 +/- 3.0% of maximal voluntary contractions (MVC) was applied throughout the task. This paradigm enabled the direct contrast of motor-unit discharge behavior during the different types of fatiguing contractions. 2. Motor-unit behavior was examined to determine the relative contribution of two mechanisms for optimizing force production under fatiguing conditions: recruitment of motor units and modulation of motor-unit discharge following recruitment. Threshold torques for motor-unit recruitment thresholds were determined by ramp-and-hold isometric contractions. Motor-unit discharge was evaluated during the fatigue task by contrasting the number of motor-unit potentials (spikes) per contraction for concentric eccentric, and isometric contractions. 3. The fatigue task resulted in a 30 +/- 12% decline in the mean MVC of elbow extension. Recruitment of nine new motor units (23%) was evident during the fatiguing extension movements, often within five to seven movements (i.e., within 25-35 s). Each newly recruited motor unit had the largest recruitment threshold torque in that experiment. 4. Analysis of the motor units that were active from the beginning of the fatigue task revealed that the mean number of motor-unit spikes per contraction increased, or remained constant as fatigue ensued, yet for the majority of motor units it increased or remained constant. None of the newly recruited motor units demonstrated decreased number of mean spikes per contraction after recruitment. Further, concurrently active motor units displayed different discharge behavior in two-thirds of the subjects. It is proposed that if the neural drive to the muscle is distributed uniformly upon the motoneuron pool, peripheral feedback from the exercising muscle may modulate specific motoneuron discharge levels during fatigue.

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Type 2 Diabetes Reduces the Muscle Anabolic Effect of Resistance Exercise Training in Older Adults

Innovation in Aging ◽

10.1093/geroni/igaa057.1706 ◽

2020 ◽

Vol 4 (Supplement_1) ◽

pp. 529-529

Author(s):

Amanda Randolph ◽

Tatiana Moro ◽

Adetutu Odejimi ◽

Blake Rasmussen ◽

Elena Volpi

Keyword(s):

Type 2 Diabetes ◽

Older Adults ◽

Muscle Strength ◽

Exercise Training ◽

Resistance Exercise ◽

Lean Mass ◽

Synthesis Rate ◽

Resistance Exercise Training ◽

Appendicular Lean Mass

Abstract Type 2 Diabetes Mellitus (T2DM) accelerates the incidence and increases the prevalence of sarcopenia in older adults. This suggests an urgent need for identifying effective sarcopenia treatments for older adults with T2DM. It is unknown whether traditional approaches, such as progressive resistance exercise training (PRET), can effectively counteract sarcopenia in older patients with T2DM. To test the efficacy of PRET for the treatment of sarcopenia in older adults with T2DM, 30 subjects (15 T2DM and 15 age- and sex- matched controls) underwent metabolic testing with muscle biopsies before and after a 13-week full-body PRET program. Primary outcome measures included changes in appendicular lean mass, muscle strength, and mixed muscle fractional synthesis rate (FSR). Before PRET, BMI-adjusted appendicular lean mass was significantly lower in the T2DM group (0.7095±0.0381 versus 0.8151±0.0439, p<0.0001). As a result of PRET, appendicular lean mass adjusted for BMI and muscle strength increased significantly in both groups, but to a lesser extent for the T2DM group (p=0.0009) . Preliminary results for FSR (n=25) indicate that subjects with T2DM had lower basal FSR prior to PRET (p=0.0197) . Basal FSR increased significantly in the control group after PRET (p=0.0196), while it did not change in the T2DM group (p=0.3537). These results suggest that in older adults the positive effect of PRET on muscle anabolism and strength is reduced by T2DM . Thus, older adults with T2DM may require more intensive, multimodal and targeted sarcopenia treatment. Funded by NIH R01AG049611 and P30AG024832.

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