Abstract
-
Introduction: Thoracic load carriage reduces pulmonary function
as a consequence of increased inertial and elastic forces. When
heavy loads are carried during periods of increased metabolic
demand, those forces can have adverse consequences on operational
lung volumes. In this investigation, the impact of a backpack
and body-armour ensemble on the ventilatory pump was explored
during a steady-state marching simulation.
Methods: Twelve males (age 24.0 y [SD 4.1], mass 81.6 kg [SD
9.5], height 1.83 m [SD 7.79]) participated in six treatments (separate
days): control trial (clothing only) plus five loading treatments
(15, 25, 35, 41, 54 kg; 75% rear distribution) using backpack and
body-armour ensemble. Subjects completed 15 min of steady-state
walking (4.8 km h−1) while metabolic, cardiorespiratory and operational
lung volumes were collected.
Results: Load carriage increased minute ventilation, heart rate
and oxygen consumption in a dose-dependent manner (p < 0.05).
For each treatment, increments in minute ventilation were primarily
achieved by significant elevations in breathing frequency
(control: 23.98 breaths/min [±1.15]; 15 kg: 26.75 [±1.18]; 25 kg:
27.74 [±1.25]; 35 kg: 30.32 [±1.37]; 41 kg: 33.81 [±1.69]; 54 kg:
37.27 [±1.51] p < 0.05), rather than tidal volume (L) (p > 0.05).
Consequently, operational lung volumes decreased in a loaddependant
manner: slow vital capacity (control: 5.19 L [±0.18];
15 kg: 4.88 [±0.14]; 25 kg: 4.66 [±0.14]; 35 kg: 4.43 [±0.15]; 41 kg:
4.31 [±0.18]; 54 kg: 3.95 [±0.22] p < 0.05); end-inspiratory lung
volume (control: 2.82 L [±0.13]; 15 kg: 2.59 [±0.12]; 25 kg: 2.55
[±0.10]; 35 kg: 2.51 [±0.09]; 41 kg: 2.35 [±0.11]; 54 kg: 2.32 [±0.11]
p < 0.05); end-expiratory lung volume (control: 1.45 L [±0.11];
15 kg: 1.25 [±0.10]; 25 kg: 1.10 [±0.08]; 35 kg: 1.00 [±0.06]; 41 kg:
0.91 [±0.07]; 54 kg: 0.80 [±0.10] p < 0.05).
Conclusions: The loaded backpack and body-armour ensemble,
when combined with elevated ventilatory requirements, reduced
these lung volumes and capacities. This was most pronounced
for the end-expiratory lung volume indicating a downward displacement
of tidal breathing along the pressure–volume relaxation
curve. This will modify the elastic and resistive work of breathing,
possibly precipitating respiratory muscle fatigue.