Growth Hormone And Testosterone Responses To Relative Loading Of Concentric And Eccentric Muscle Actions

Abstract

Applying the same constant muscle loads in an earlier study, we showed that concentric (CON) muscle contractions were associated with greater GH but similar T responses than eccentric (ECC) muscle contractions, and attributed the GH difference to a greater relative CON load. PURPOSE The purpose of the present study was to determine whether GH would respond in a similar fashion to CON and ECC muscle actions using constant relative loads. METHODS Seven young men (mean±SE age 25.7±2.17 y; weight 98.5±8.92 kg) with recreational weight training experience completed CON and ECC muscle contraction trials in a counterbalanced fashion. The exercises consisted of 4 sets of 10 repetitions of lat pull-down, leg press, bench press, leg extension, military press, and leg curl exercises at 65% of a CON or an ECC 1-RM with 90 s between sets and exercises. ECC 1-RMs were considered to be 120% of the CON 1-RM for the same exercise. Blood samples were collected 20 min before, at the conclusion of, and 15 min after the exercise. RESULTS Serum GH significantly increased from rest to postexercise for the CON trial (from 0.099±0.38 to 5.58±2.46 ng/mL] and the ECC trial (from 0.019±0.01 to 4.72±1.78 ng/mL), but was not different between the two trials. Total testosterone from rest to postexercise for the CON trial (from 374.7±45.79 to 451.14±50.56 ng/mL) and the ECC trial (from 438.0±50.56 to 445.86±62.58 ng/mL) was not significantly altered. However, free testosterone concentrations significantly increased in response to CON (from 16.3±2.75 to 17.1±2.61 ng/mL) and ECC (from 15.86±1.79 to 17.79±2.05 ng/mL) trials, but were not different from each other. Although RPE was similar between trials, lactate levels were greater for the CON trial. CONCLUSIONS Data suggest that CON and ECC muscle contractions produce similar GH, T, and FT responses when loading is relative to a 1-RM (ECC @ 120% of CON 1-RM) for the specific muscle action.