Abstract
This thesis describes experiments designed to examine ventilatory function and respiratory muscle fatigue during thoracic load carriage (LC) exercise, in the context of military task performance. Three experimental studies were conducted to: a) identify whether British Army Infantry soldiers with prior LC experience possess stronger respiratory muscles than the physically active civilian population and assess their ventilatory responses to 25 kg LC exercise; b) compare the physiological and biomechanical responses to LC exercise with heavier loads (40 kg) and lighter loads (25 kg) in British Army Infantry soldiers; c) determine the effects of respiratory muscle fatigue (RMF) on military task performance (i.e. loaded march and marksmanship) in Royal Marines Commandos.Prior military LC experience in British Army Infantry soldiers (recent tours and exercises carrying loads between ~25 kg to ~55 kg for ~1 hour to 12 hours in the preceding 6 months) did not prevent LC- induced RMF. Neither did it confer any advantage in respiratory muscle strength or the ventilatory responses to LC exercise, beyond that exhibited by physically active civilians. These findings suggest that being physically active may offer similar respiratory muscle resilience and performance outcomes in LC tasks as prior military LC experience. As such, naïve load carriers (e.g. recruits) with good baseline aerobic fitness (estimated V̇O2max: ~46 mL·kg-1·min-1) may be able to perform 25 kg LC exercise adequately – promoting a higher V̇O2max during military recruitment and training could offer a degree of protection. Additionally, increasing the mass carried from 25 kg to 40 kg did not exacerbate RMF in soldiers and was not related to any changes in posture and gait. Consequently, 25 kg loads can provide a sufficient training stimulus to the respiratory muscles for soldiers in situations where 40 kg loads are not accessible. This has the benefit of potentially reducing the likelihood of injury associated with carrying much heavier loads. The superior aerobic fitness (estimated V̇O2max: ~53 mL·kg-1·min-1) and respiratory muscle strength (PImax: 153 cmH2O; PEmax: 219 cmH2O) exhibited in the Royal Marines Commandos (time in service: 77 ± 31 days) did not prevent RMF occurring and more than 30 minutes was required for full recovery. Notwithstanding, RMF did not impact simulated marksmanship or LC (30.25 kg) 4 km exercise performance.
A high degree of inter-individual variability in the magnitude of RMF exhibited was present in all studies. Some individuals may be uniquely robust to withstand the potential deleterious effects of RMF on military task performance, whilst others are affected – the military population is not a homogenous group. As such, further work should be conducted to establish whether the findings reported in this thesis persist with lower levels of fitness and in different job roles within the military population.
| Date of Award | 20 Oct 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Mitch Lomax (Supervisor), Gemma Milligan (Supervisor) & Mike Tipton (Supervisor) |