Intra-session Reliability Of Strength And Evoked Measures During Isometric Muscle Actions In Men

PURPOSE: Evoked measures such as voluntary activation (%VA), central activation ratio (CAR), and potentiated twitch torque (PTT) are often used to assess changes in neuromuscular performance. Little is known, however, regarding the reliability of these measures for the upper body. Therefore, this study assessed the intra-session reliability for the torque, %VA, CAR, and PTT of the forearm flexors. METHODS: Twelve men (mean ± SD: age = 21.3 ± 1.8 yrs) performed forearm flexion maximal voluntary isometric contractions (MVICs) at baseline (T1) and after a 10-min rest period (T10) over three different sessions (S1, S2, and S3) each separated by 48-hrs. Transcutaneous, supramaximal electrical stimuli were delivered to the motor point of the biceps brachii during each MVIC (i.e., superimposed twitch), and at rest after each MVIC (i.e., potentiated twitch). The %VA and CAR were calculated as %VA = [1-(superimposed twitch/potentiated twitch)] × 100 and CAR = [MVIC/(MVIC + superimposed twitch)] × 100, respectively. Intra-session reliability was assessed from T1 versus T10 during S1, S2, and S3. Repeated measures ANOVAs were used to assess systematic error and a 2,1 model was used to determine the intraclass correlation coefficient (ICC), standard error of the measurement (SEM), and minimal difference (MD). RESULTS: There were no significant (p > 0.05, range = 0.279-0.817) mean differences for any of the test versus retest measures. The ICCs indicated that MVIC torque (range = 0.969-0.983), %VA (range = -0.143-0.460), CAR (range = -0.031-0.162), and PTT (0.290-0.808) reflected poor to excellent reliability. The SEMs for MVIC torque, %VA, CAR, and PTT ranged from 2.2-2.3 Nm, 2.3-7.6 %, 0.4-0.6 %, and 0.9-3.0 Nm, respectively. The MDs for MVIC torque, %VA, CAR, and PTT ranged from 6.0-6.3 Nm, 14.7-21.1 %, 1.1-1.6 %, and 2.4-8.2 Nm, respectively. CONCLUSIONS: These findings indicated that MVIC torque had the highest reliability, while %VA had the lowest reliability. Furthermore, the SEMs indicated low precision for the %VA values, and the MDs for %VA suggested that the magnitude of change needed to be considered real is larger than what is often demonstrated. Therefore, MVIC, CAR, and PTT may serve as more reliable and sensitive measures of fatigue-induced changes in neuromuscular performance.