Similar hormonal responses to concentric and eccentric muscle actions using relative loading

Area of Science:

• Exercise Physiology
• Endocrinology
• Sports Science

Background:

• Conventional resistance training involves sequential concentric (CON) and eccentric (ECC) muscle contractions.
• Previous research indicated greater growth hormone (GH) response with absolute concentric loading compared to eccentric.
• The role of relative loading on endocrine responses (GH, total testosterone [TT], free testosterone [FT]) requires further investigation.

Purpose of the Study:

• To investigate and compare the endocrine responses (GH, TT, FT) to CON and ECC muscle contractions under relative loading conditions.
• To test the hypothesis that relative loading would result in similar GH responses but greater TT and FT responses after ECC contractions.

Main Methods:

• Seven recreationally trained young men participated in a counterbalanced study.
• Participants completed six upper and lower body exercises (lat pulldown, leg press, bench press, leg extension, military press, leg curl) in both CON and ECC trials.
• Exercises were performed at 65% of a 1-repetition maximum (1-RM) for each contraction type, with ECC 1-RM set at 120% of CON 1-RM. Blood samples were collected pre-exercise, immediately post-exercise, and 15 minutes post-exercise.

Main Results:

• Growth hormone (GH) levels significantly increased in both CON and ECC trials, with no significant difference between the two.
• Total testosterone (TT) levels did not show significant alterations in either trial.
• Free testosterone (FT) concentrations increased significantly following both CON and ECC contractions.

Conclusions:

• Under relative loading conditions, both CON and ECC muscle contractions elicit similar GH responses.
• Relative loading results in comparable increases in total and free testosterone for both CON and ECC contractions.
• These findings suggest that the type of muscle contraction (CON vs. ECC) may not differentially impact endocrine responses when normalized for relative intensity.