Acute Testosterone Deficiency Affects Electrical Properties Of Elbow Flexors And Extensors During Voluntary Contractions

Abstract

Testosterone (T) is a powerful androgenic anabolic steroid (AAS) capable to induce diverse biological modifications both in the nervous system and in the skeletal muscle. Nevertheless, no previous study investigated the effect of T on the neuromuscular control in intact human muscles. PURPOSE: This study aims at assessing the acute effects of reduced T serum concentration on the neuromuscular control in intact human muscle. METHODS: Off-therapy hypogonadal (HY= 9) and eugonadal (EU = 15) volunteers were asked to perform isokinetic elbow flexion-extension at different angular velocities (AV: 0-30-60-120-180- 240°/s). For any considered AV, three cycles were performed. Between each attempt (AV), 5-minute rest were granted. Surface electromyograms (sEMG) of Biceps Brachii (BB) and Triceps Brachii (TB) were recorded in differential mode with two four linear array electrodes. sEMG and torque data were recorded synchronously at a sampling frequency of 2048 Hz. For any AV, during flexion and extension, the maximal torque among the three cycles was detected and used to compare group means. For both BB and TB and for all the considered AV, agonist (AGBB; AGTB) and antagonist (ANBB; ANTB) activation was expressed as a ratio of the agonist activation observed at 0°/s. Furthermore, the median frequency (MDF) of the sEMG power spectrum was computed for both the BB and the TB (MDFBB; MDFTB) at any AV considered. Muscle fiber conduction velocity of the BB (CVBB) was estimated as well. RM-ANOVA was performed to compare group means in mechanical and electromyographic parameters. RESULTS: No main effect of group was observed for peak torque, during flexion (p = .38) and extension (p = .74) and for AGBB (p = .44), AGTB (p = .93), ANBB (p = .99) and ANTB (p = .96). A significant effect of group was observed for MDFTB (p = .02; group mean ± SD. EU: 97.1 ± 14.0; HY: 83.5 ± 9.4) and a trend (p = .05) towards lower MDFBB in the HY group (group mean ± SD. EU: 88.1±15.0; HY: 77.1±13.9). The HY group showed a trend towards lower CVBB (p = .06; EU: 4.5 ± 0.6; HY: 4.1 ± 0.2) CONCLUSION: Since MDF and CV have been associated with motor unit recruitment strategies, the lower MDF and CVBB observed in the HY group seem to reflect a decreased ability to recruit motoneuron pools, which might lead to the well documented force loss following chronic exposure to a reduced T concentrations.