Dose-and gender-specific effects of resistance training on circulating levels of brain derived neurotrophic factor (BDNF) in community-dwelling older adults.

BACKGROUND BDNF is known to induce neuroplasticity and low circulating levels have been related to neuronal loss in older persons. Physical exercise is thought to trigger BDNF-induced neuroplasticity, but conflicting observations have been reported regarding the effects of resistance training on circulating BDNF in the elderly. These conflicting observations might reflect dose-and gender-specific differences. METHOD Fifty-six apparently healthy elderly (68 ± 5 years) participants were randomized to 12 weeks of resistance training (3×/week) at either high-resistance (HIGH, 8 Males, 10 Females, 2 × 10-15 repetitions at 80% 1 RM), low-resistance (LOW, 9 Males, 10 Females, 1 × 80-100 repetitions at 20% 1 RM), or mixed low-resistance (LOW+, 9 Males, 10 Females, 1 × 60 repetitions at 20% 1 RM followed by 1 × 10-20 repetitions at 40% 1 RM). Serum was collected for BDNF assay at baseline and after 12 weeks (24 h-48 h after the last training). RESULTS 12 weeks of LOW+ exercise significantly increased BDNF levels in male (from 34.9 ± 10.7 ng/mL to 42.9 ± 11.9 ng/mL, time × group interaction p=0.013), but not in female participants. No significant change was observed in HIGH or LOW, neither in male nor female subjects. CONCLUSION Our results show that only the mixed-low-resistance training program with a very high number of repetitions at a sufficiently high external resistance was able to increase circulating BDNF in older male participants. Training to volitional fatigue might be necessary to obtain optimal results. Additional studies are needed to unravel the underlying mechanisms, as well as to confirm the observed gender difference.