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F19U FREE COMMUNICATION/POSTER SKELETAL MUSCLE II

INTERPRETATION OF CHANGES IN RMS DURING FATIGUING CYCLE EXERCISE MUST CONSIDER PEDAL FREQUENCY

Barstow, T J. FACSM1; Scheuermann, B W.1; Frazier, B C.1; Meadows, K D.1

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Medicine & Science in Sports & Exercise: May 2001 - Volume 33 - Issue 5 - p S263
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During fatiguing constant power output (PO) exercise on a cycle ergometer, an increase in RMS from surface EMG has been interpreted to represent additional recruitment of motor units (MU). However, fatigue is also associated with reduced pedal rate, which would require greater force/pedal stroke, which itself would be associated with greater RMS. To further evaluate these relationships, we examined the pattern of change in RMS during fatiguing cycle ergometer exercise at 90, 100 and 110% of the power output obtained during incremental exercise. 21 subjects (15 males) performed 3 bouts of constant work rate cycle exercise to fatigue on different days. Surface EMG of the vastus lateralis was obtained for each trial. RMS for each muscle contraction during exercise was determined off-line. Changes in RMS from the first 20 s of exercise to the last 20 sec preceding fatigue were calculated. In addition, RMS was divided by an index of the average torque per stroke (as PO/pedal frequency), and changes in this term were calculated as for RMS. For all three work intensities, correcting the RMS for changes in torque due to alteration in pedal frequency led to significant reduction in the percent change over the duration of the exhausting exercise (mean increase 37%), compared to changes in the uncorrected RMS (50–60%, P < 0.001). Thus, 27–38% of the increase in RMS during this fatiguing exercise could be attributed to changes necessary to meet force requirements at a lower rpm, with the remainder possibly reflecting increased MU recruitment as fatigue develops. These results point out the need to consider changes in muscle force consequent to changes in pedal frequency when interpreting changes in RMS to reflect MU recruitment patterns during fatiguing exercise on electrically-braked cycle ergometers. Supported by NIH HL46769

©2001The American College of Sports Medicine