Validation of a 5 Minute 5 Hz protocol for Muscle Specific Endurance

Abstract

Muscle endurance has been measured using an electrical stimulation twitch protocol and an accelerometer.  This protocol used stimulation frequencies of 2, 4, and 6 Hz over nine minutes.  This study compared endurance index values using a shorter protocol of 5 Hz for 5 Minutes to the original nine minute protocol. Fifteen healthy subjects (19-22yrs) were electrically stimulated on the forearm muscles twice: one day for 5 minutes at 5 Hz and on another day for 3 minutes at each at 2, 4 and 6 Hz. A triaxial accelerometer measured the resultant vector of the movements and the decrease in acceleration was used to indicate fatigue. There was no difference in Endurance Index (EI) between the 5 and 9 minute protocols (63.2+18.7%, 64.1+19.8%, respectively, p=0.532). The correlation between the two EI measurements was y= 0.91x+4.99%, r2=0.93. Equivalency testing found the mean difference between EI values for the two methods was 0.88% with a 95% confidence interval of the difference in EI of -2.09 to 3.81%. In conclusion, the shorter 5 Hz five minute endurance index protocol provided similar results to the longer 2 ,4, 6 Hz nine minute protocol. These results support the use of the shorter protocol when measuring muscle specific endurance.