Reliability of the repetition-to-fatigue method for estimating one-repetition maximum in unilateral strength exercises and its relationship with gait tests in people with multiple sclerosis

Objective: to analyze the reliability of the estimated one-repetition maximum (e1RM) through the repetition to fatigue method in four unilateral resistance training exercises performed using weight machines (i.e., leg press, calf raises, leg extension, seated leg curl), and their relationship to gait-related tests.

Design: cross-sectional study.

Setting: university sports complex.

Participants: twenty-four participants with multiple sclerosis completed three testing sessions. They performed three testing sessions that were integrated into a long-term multimodal exercise regime comprising strength, balance, and functional mobility exercises, conducted twice a week in 90-minute sessions.

Main outcome measures: the first session consisted in the assessment of the gait-related tests [i.e., timed up and go (TUG), timed 25-foot walk (T25FW), 6-minute walk (6MW)]. Two testing sessions were dedicated to the assessment of the e1RM in the aforementioned exercises.

Results: intraclass correlation coefficients (ICC_2.1) of absolute e1RM ranged from 0.92 to 0.97 and they were slightly higher than those relative to the body mass (0.85<ICC_2.1<0.96). Typical errors for the four exercises ranged between 2.2 and 4.7 kg (9.3 - 11.6%). The weaker leg e1RM for the calf raises and leg curl exercises were significantly associated with the 6MW (0.654≤r≤0.677), T25FW (-0.555≥r≥-0.557) and TUG (-0.480≥r≥-0.526). Between-leg e1RM asymmetries in these exercises were also correlated to the 6MW (0.420≤r≤0.467), T25FW (0.553≤r≤0.590) and TUG (0.626≤r≤0.627). Unilateral e1RMs during the leg press and leg extension showed no or few significant associations with gait-related tests.

Conclusions: the results suggest that e1RM can be safely and reliably performed to quantify single-leg strength and to control the training load in these exercises. Knee flexors and ankle extensors strength, especially of the weaker leg, along with their asymmetry, seem to be the most relevant factors to consider in the strength assessment and training of this population.