The Effect of Local Muscle Cooling on Muscle Activation and Fatigue

THE EFFECT OF LOCAL MUSCLE COOLING ON MUSCLE ACTIVATION AND FATIGUE A. Barnett, S. Ross, A. Guevara, A. Morse, R.S. McCulloch PURPOSE: To determine the effect of cooling on upper arm muscle activation and fatigue during an isometric bicep curl. METHODS: Sixteen untrained females performed 2 trials of isometric dumbbell holds (IDH) to fatigue. Using a force transducer, maximum force producing capability was measured during an isometric biceps curl. Twenty percent of this maximum force was used as the subject’s specified dumbbell weight for IDH. In the local muscle cooling trial (LMC), ice packs were applied to subjects’ biceps and triceps brachii for 20 minutes. The thermoneutral trial (TN) involved a 20-minute rest without ice before IDH. During IDH, subjects were instructed to hold their specified dumbbell at 90 degrees of elbow flexion until fatigue. Fatigue was reached when subjects voluntarily ended the hold or when elbow flexion exceeded 100 degrees as measured by a goniometer. Muscle activity of the biceps and the triceps, normalized to subjects’ maximal voluntary contractions (MVC) was collected using electromyography (EMG). Core and skin temperature were collected before and after the 20 minute intervention, and after IDH. Normalized muscle activation, EMG median frequency, time of hold (TH), and % coactivation (triceps:biceps) were compared between LMC and TN trials using paired t-tests. IDH EMG information was divided into 3 intervals; interval 1 (0-1 minutes), interval 2 (3-4 minutes), and interval 3 (final minute). RESULTS: There was a significant difference in TH between LMC (516.51±143.13 s) and TN (449.39±85.25 s, p=.021). There was 67.1% more coactivation during TN vs. LMC in interval 1 (p = .005), 63.2% more coactivation during TN in interval 2 (p =.007 ), and 60.7% more coactivation during TN in interval 3 (p=.006).The biceps brachii was 5.4% more active in interval 1 (p=.024) and 6.6% more active during interval 3 (p=.027) in LMC vs. TN. In TN, the median frequency was 10.2 Hz greater for the biceps brachii (p=.009) and 7.5 Hz greater for the triceps brachii (p=.032) in interval 1 CONCLUSION: During IDH, LMC attenuated fatigue, increased biceps brachii activity, decreased median frequency, and decreased the coactivation ratio. LMC may provide benefits for athletes who utilize isometric contractions in their sports to prolong endurance through possible increase of pain tolerance and promotion of a more economical contraction