Relationship Between Muscle Activity And Isometric Force During Submersion In Shallow Water.

Abstract

Shallow and deep water running are used by athletes as either substitute or in addition to running on land. However, it is not clear if the relationship between the ability to generate force and electromyography (EMG) is influenced by water submersion. PURPOSE: Compare isometric force-EMG relationship during on land and submersion in shallow water. METHODS: Participants (n=4; 29.7±20.2 yrs, 1.80±0.1 m, 82.2±24.3 kg) were fit with leads to measure rectus femoris (RF) EMG using a telemetry EMG system (Noraxon, 1000 Hz) while wearing a drysuit. Participants sat in a chair with the ankle secured in a cuff and knee angle at 90 degrees of flexion. One end of the cable was attached to the cuff and the other to a linear force transducer which was always above water level. The transducer measured the tension force created with the cable that resisted knee extension. The chair was portable and was used on the deck of a pool and in shallow water. Force data were recorded concurrent with EMG data. Participants completed four 5-sec isometric knee extension conditions ranging from submaximal to maximal effort. The maximal effort condition was always done first with submaximal efforts targeting 25%, 50%, and 75% of maximal effort with real time verbal feedback provided. Participants always completed these conditions on land first then in water submerged to about the xiphoid process while sitting. Rest was provided as needed between conditions. EMG data were processed by removing any offset and full-wave rectifying. Force and EMG data were each averaged over the last 1-sec. Force-EMG plots were generated for each participant for on land and in water data sets and fit with linear lines of best fit. The y-intercepts and slopes were recorded and each compared between on land and in water using paired t-tests (α=0.05). A group line of best fit was also calculated for descriptive purposes. RESULTS: The group linear line of best fit for Force-EMG during Land was EMG=2.3005(Force) + 4.9007 (R2 = 0.9819) and during water was EMG=2.1759(Force) - 4.7535 (R2=0.9874). Using individual data sets, neither the slope (p=0.133) nor y-intercept (p=0.131) were different between on land and in water. CONCLUSIONS: The relationship between knee extension force and EMG was the same while on land and in the water.