Intra-rater reliability of electromyographic recordings and subjective evaluation of neck muscle fatigue among helicopter pilots.
The aim was to evaluate the reliability of a method of measuring neck muscle fatigue among helicopter pilots.


METHODS
Surface EMG from three areas in the neck region, bilaterally, was recorded among 10 male helicopter pilots while they were performing isometric contractions in flexion and extension for 45 s, sustaining a force representing 75% of maximum strength in a seated position. Perceived fatigue was rated using the Borg CR-10 scale. The test was repeated twice the first day and then two additional times with one-week intervals. Variables analyzed were the slope of the median frequency change, the normalized slope, and the ratings after 15, 30 and 45 s; and also the initial median frequency (IMDF). The intra-class correlation (ICC) and the measurement error (S(w)), intra- and inter-day were calculated statistically.


RESULTS
The best reliability for the slope was found for the 45 s intra-day analysis taking all measurements into account (ICC 0.65-0.83). The reliability after 30 s was poorer but still acceptable (ICC 0.52-0.71). For the subjective ratings, the highest reliability was found after 30 s inter-day (ICC 0.86-0.88). IMDF showed generally high reliability for the intra-day analyses (ICC 0.63-0.80).


CONCLUSIONS
The method is reliable for use in further research. Since performing a contraction of 75% of maximum was quite strenuous, we recommend that the protocol be shortened to 30 s.
Thuresson
Marcus
M
Section of Physiotherapy, Neurotec Department, Karolinska Institutet, Stockholm, Sweden. marcus.thuresson@neurotec.ki.se
Ang
Björn
B
Linder
Jan
J
Harms-Ringdahl
Karin
K
D000328:Adult; D000337:Aerospace Medicine; D000401:Aircraft; D001294:Attitude to Health; D004576:Electromyography / Q000706:statistics & numerical data; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D009334:Neck Muscles / Q000502:physiology*; D011187:Posture / Q000502:physiology; D015203:Reproducibility of Results; D013997:Time Factors