Eight weeks of heavy strength training increases hemoglobin mass and V̇o2peak in well-trained to elite female and male rowers

Abstract

O₂-transport and endurance exercise performance are greatly influenced by hemoglobin mass (Hb_mass), which largely depends on lean body mass (LBM). This study investigated the effects of 8 wk with three weekly sessions of conventional (3-SET: 3 × 10 reps) or high-volume strength training (10-SET: 5-10 × 10 reps) on LBM, Hb_mass, muscle strength, and exercise performance in female and male rowers. Hematological parameters were obtained through CO rebreathing and body composition by dual-energy X-ray absorptiometry (DEXA) scans before and after the training period. Concomitantly, V̇o_2peak was determined during 2-km ergometer rowing and muscle strength by isometric midthigh pull. There were no differences in training responses between groups for any of the parameters. Pooled data revealed overall increments for Hb_mass (10-SET: 882 ± 199 g to 897 ± 213 g; 3-SET: 936 ± 245 g to 962 ± 247 g, P = 0.02) and V̇o_2peak (10-SET: 4.3 ± 1.0 to 4.4 ± 0.9 L·min^-1; 3-SET: 4.5 ± 0.9 to 4.6 ± 0.9 L·min^-1, P = 0.03), whereas LBM remained unchanged (10-SET: 58.7 ± 10.5 to 58.7 ± 10.1 kg; 3-SET: 64.1 ± 10.8 to 64.5 ± 10.6 kg, P = 0.42). Maximal isometric midthigh pull strength increased (10-SET: 224 ± 47 kg to 237 ± 55 kg; 3-SET: 256 ± 77 kg to 281 ± 83 kg, P = 0.001). Strong associations were observed between LBM and Hb_mass and V̇o_2peak (r² = 0.88-0.90), entailing sex differences in Hb_mass and V̇o_2peak. Normalizing V̇o_2peak to LBM reduced the sex difference to ∼10%, aligning with the sex difference in Hb_mass·LBM^-1. Strength training successfully increased Hb_mass and V̇o_2peak in elite female and male rowers, without an additional effect from increased training volume. Moreover, sex differences in V̇o_2peak were mainly explained by differences in LBM, but likely also by differences in Hb_mass·LBM^-1.NEW & NOTEWORTHY This study in female and male rowers demonstrates that hemoglobin mass (Hb_mass), V̇o_2peak, and muscle strength increases with 8 wk of heavy strength training and that this response is not different between conventional (3 × 10 repetitions) and high-volume strength training (10 × 10 repetitions). Moreover, female rowers exhibited less hemoglobin per kilogram of lean body mass compared with their male counterparts, which likely contributes to sex differences in V̇o_2peak and rowing performance.

Keywords: blood volume; muscle strength; oxygen uptake; performance; rowing.