EARLY AND LATE RAPID NEUROMUSCULAR PARAMATERS OF THE PLANTAR FLEXORS IN MIDDLE-AGED AND OLDER MALES

Abstract

Rapid torque production is important for physical function in older adults. Early and late rapid torque parameters are influenced by different physiological factors; therefore, they may be differentially affected by aging. Few comparisons exist between middle-aged and older adults for early and late rapid torque measures. PURPOSE: To compare early and late rapid torque measures of the plantar flexors (PFs) in middle-aged (MM) and older males (OM). METHODS: Twenty-nine MM (n=14; 45.3±2.6 yrs) and OM (n=15; 65.3±3.2 yrs) performed maximal voluntary isometric contractions of the PFs using a dynamometer. Peak torque (PT), as well as rate of torque development (RTD; Δtorque/Δtime) and impulse (area under the curve) during the early (0-50 ms; RTD0-50, IMP0-50) and late (100-200 ms; RTD100-200, IMP100-200) contraction phases were calculated. Torque at 50 (TQ50), 100 (TQ100), and 200 ms (TQ200) was also obtained. Additionally, RTD and TQ variables were normalized to PT. The onset was 2.5 Nm for all torque variables. Electromyography of the medial gastrocnemius was recorded in order to obtain rate of electromyography rise (RER). RER was calculated as the linear slope of the normalized electromyography signal at 30, 50, and 75 ms from the onset. Independent samples t-tests were used for group comparisons. RESULTS: PT (p=0.105), TQ50 (p=0.156), early (p=0.162), and late (p=0.074) RTD were similar between groups. TQ100 (MM=69.71±16.85 vs. OM=55.99±18.54 Nm·s-1; p=0.046), TQ200 (MM=114.76±26.79 vs. OM=91.56±28.10 Nm·s-1; p=0.031), and IMP100-200 (MM=4.79±1.11 vs. OM=3.83±1.17 Nm·s; p=0.032) were lower in OM. Normalized torque variables showed no differences (p>0.05). RER (p=0.057-0.072) was similar between groups. CONCLUSIONS: Our data indicates that late rapid torque parameters of the PFs were preferentially influenced by age, yet PT appeared to mediate this result. Although not significant, the effect sizes for RER (d=0.69-0.74) may suggest that rapid muscle activation was influential as well.