WITHIN-SESSION RELIABILITY OF THREE METHODS OF ELECTROMYOGRAPHY NORMALIZATION FOR HAMSTRING AND GLUTEAL MUSCLES

PURPOSE: The purpose of the current study was to compare the reliability of three methods for EMG normalization for the hamstring and gluteal muscles. The methods used were; prone lying isometric hip extension (0o) and knee flexion (55o) performed on an isokinetic dynamometer (IKD HIP, IKD KNEE); prone lying isometric hip extension (0o) and knee flexion (55o) with manual resistance applied to the distal thigh (MAN HIP, MAN KNEE) and as a standing squeeze of the gluteal muscles (GS) and hamstrings (HS). METHODS: Ten healthy resistance-trained participants (Age: 23.1 ± 3.5 years; Height: 176.4 cm ± 6.6 cm; Mass: 79.1 kg ± 12.8 kg; 4 Female; 6 Male) volunteered to participate in this study. EMG electrodes were positioned as per the SENIAM guidelines. Raw EMG data were captured at 1500 Hz, with high- and low-pass filtering between 10-1000 Hz. Root mean square values were calculated in a bespoke spreadsheet, using a 200 ms moving average window. Mean and SD were calculated across each trial relating to peak EMG amplitudes. Each participant completed three eight-second, maximal isometric contractions of both limbs across each test in a randomised order, with a 30 second rest between trials. Within-session reliability was assessed using the intraclass correlation coefficient (ICC 2,1), and coefficient of variation (CV), with acceptable reliability set at ≥0.8 and ≤12%, respectively. One-way repeated measures analysis of variance with post-hoc Bonferroni analyses, were completed to determine differences between tests. RESULTS: The results of the current study indicate that the MAN HIP and MAN KNEE methods of normalization produce acceptable levels of reliability for the hamstring muscles, however the 95% CIs were broader for the MAN KNEE. The IKD HIP method produced the greatest reliability for the gluteal muscles (Table 1). There was no significant difference in EMG amplitude between any of the MAN and IKD methods. There was no significant difference across any of the EMG amplitudes for the gluteal muscles. The HS method produced significantly lower EMG peak amplitude than any of the other methods used. CONCLUSIONS: MAN HIP and MAN KNEE methods produce comparable peak EMG amplitudes, with acceptable levels of reliability. The IKD HIP method produced the most reliable results for gluteal normalization. Although the MAN HIP and GS methods have been suggested elsewhere, the poor CV may leave researchers vulnerable to unreliable normalization of EMG. PRACTICAL APPLICATIONS: The MAN HIP and MAN KNEE methods provide researchers with time-efficient and reliable methods of normalizing EMG, with no significant differences in peak EMG amplitudes. The MAN HIP method may be advised, given the broader 95% CIs reported in the current study. The IKD HIP method should be used to maximize reliability in the gluteal muscles, however, does come with considerable time constraints. Should researchers opt for the MAN HIP methods for the gluteal muscles, it is paramount that researchers screen CV of their measures to minimise variability.