The effect of two concurrent training programs with different inter-session recovery on musculoskeletal strength

Background. Gains in musculoskeletal strength acquired via concurrent strength and endurance training have been of lesser magnitude when compared to those acquired when performing strength training alone. This attenuation in strength may be due to a lack of recovery from the high volume of exercise characteristic of concurrent training. Purpose. The purpose of this study is (a) to evaluate the relative effectiveness of two concurrent training regimens, differing only in the duration of the rest between the strength and endurance training sessions, with regard to increasing strength and (b) to determine if the responses of testosterone and cortisol and the changes in FFM, RMR, and blood urea nitrogen can be identified as contributing factors in this phenomenon. Methods. Twenty-four physically active, untrained males (21 +/- 1.37 years) completed six weeks of training in one of three groups: a same day concurrent training (SDCT, N=8), an alternate day concurrent training (ADCT, N=10), or a strength training only group (ST, N=6). Body composition measures (body weight, percent body fat, FFM, fat mass), RMR, blood urea nitrogen, VO2max, 1RM bench press, 1RM hac-squat, daily total caloric intake, and percentage energy macronutrients were measured before and after training. Salivary testosterone, salivary cortisol, and the salivary T:C were measured pre-, mid-, and post-training. All data was analyzed using the appropriate 2-way ANOVA with repeated measures. Results. 1RM bench press, 1RM hac-squat, VO2max, body composition measures, RMR, salivary cortisol, and fat consumption significantly increased from pre- to post-training. The only significant interaction was that of blood urea nitrogen, which decreased in the SDCT group and increased in the ST group from pre- to post-training. Conclusions. The lack of any significant difference among the study groups regarding musculoskeletal strength, cardiorespiratory endurance, body composition, and RMR does not support the existence of an interference phenomenon regarding the musculoskeletal adaptations to concurrent training.