Kyphotic Posture Reduces Respiratory Efficiency During Walking and Running

Altered spinal alignment can affect ventilatory mechanics, yet the acute impact of kyphotic posture during dynamic exercise remains unclear. This study aimed to examine the acute effects of a simulated kyphotic posture on ventilatory efficiency during treadmill standing, walking, and running in healthy young adults. We hypothesized that kyphotic posture would increase ventilatory burden, particularly at higher exercise intensities.

Ten healthy young men completed two postural conditions (kyphotic and neutral) while standing, walking (4 km/h), and running (10 km/h) on a rehabilitation treadmill (Biodex Medical Systems, Inc., Shirley, NY, USA). Spinal curvature was quantified using three-dimensional motion capture (VICON Motion Systems Ltd., Oxford, UK; 50 Hz) as the spinal curvature angle (θ) defined by the C7-PSIS-midpoint and C7-T10 lines. Breath-by-breath gas exchange was measured using Aeromonitor AE-310s (Minato Medical Science Co., Ltd., Osaka, Japan) under controlled ambient conditions. The variables included oxygen uptake (VO₂), carbon dioxide output (VCO₂), mass-specific oxygen uptake (VO₂/W), respiratory exchange ratio (RER), respiratory rate (RR), minute ventilation (VE), end-tidal oxygen (ETO₂), end-tidal CO₂ partial pressure (ETCO₂), VE/VO₂, VE/VCO₂, and physiological dead space to tidal volume ratio (VD/VT). Steady-state values were extracted from the final 1-min epoch of each condition (<5% coefficient of variation for VO₂ over 30 s). Paired t-tests or Wilcoxon signed-rank tests were used as appropriate; effect sizes were reported as dz (t-tests) or rrb (Wilcoxon) with 95% confidence intervals (CIs) (α=0.05).

Kyphotic posture significantly increased spinal flexion during all tasks. At rest, the kyphotic posture showed a higher RR and ETCO₂, lower ETO₂, and higher VD/VT than the neutral posture (all p≤0.05). During walking (4 km/h), the RER was higher in the kyphotic posture (p=0.049), and ETCO₂ remained elevated; VO₂ and VO₂/W did not differ, whereas VCO₂ and VE/VCO₂ showed non-significant trends. During running (10 km/h), the kyphotic posture produced higher VCO₂ (p=0.036) and RER (p=0.004), with a non-significant trend toward higher VE; VO₂ and VO₂/W remained comparable between the postures. Across conditions, several effects were supported by confidence intervals consistent with posture-related differences, despite the modest sample size of the study.

A transient, simulated kyphotic posture was associated with a small but consistent increase in ventilatory burden during dynamic exercise in healthy young men, reflected by higher ETCO₂ at rest, higher RER during walking and running, and higher VCO₂ during running, despite similar VO₂. These preliminary findings warrant confirmation in larger, sex- and age-diverse cohorts, including individuals with structural kyphosis.