Effects of body posture and exercise training on cardiorespiratory responses to exercise

The primary aims of the present study were to evaluate cardiorespiratory responses to incremental head down tilt exercise and to determine if the cardiorespiratory adaptations obtained from endurance training in the head down tilt posture transfer to the upright posture. 22 men (25 ± 3 years) performed V˙O2peak cycle exercise tests in the upright and head down tilt postures. Of these, 11 men were endurance trained on a cycle ergometer in the upright posture for 8 weeks (upright training group; UTG) or in the upright posture for 4 weeks followed by 4 weeks in the head down tilt posture (head down training group; HTG). During acute exercise, V˙O2peak was decreased in the head down tilt posture compared to upright (2.01 ± 0.51 vs. 2.32 ± 0.61 l/min respectively, P < 0.05). Stroke volume (SV) at 100 W was greater during head down tilt cycling compared to the upright (77 ± 5 vs. 71 ± 4 ml/beat, P < 0.05). Following training V˙O2peak increased in both groups during upright exercise. However, V˙O2peak during head down tilt cycling was only increased in the HTG. Sub-maximal and peak SV in the HTG increased in both upright and head down tilt postures. SV in the UTG increased only in the upright posture and was unchanged during head down tilt cycling. In conclusion, acute head down tilt exercise increases sub-maximal SV compared to upright exercise. Furthermore, training in the head down tilt posture induces cardiorespiratory adaptations in both upright and head down tilt postures, while the adaptations to upright exercise training are primarily observed when upright exercise was performed.