Physiological and biomechanical analysis of prolonged and repeated bouts of load carriage

Previous work has attempted to define the physiological determinants of load carriage over a single day of load carriage, primary aims of this thesis were to determine the physiological and biomechanical changes as a result of load carriage and to explore the causes of these changes during load carriage and to explore these changes over multiple days of activity. A secondary aim was to explore individual differences in performance and possible mechanisms for this.

Chapter 4 observed acute changes in vertical ground reaction force, supported by effect sizes which suggests individual differences in performances (loading peak dCohens=1.66 and dGlass 4.49). These findings were supported by no change in first negative rate which suggests increased knee flexion is occurring to mitigate the effect of the load. Differences in anteroposterior ground reaction force variables suggest that changes in gait may affect movement economy. Energy expenditure was shown to be correlated to a number of strength variables, such as ankle plantarflexion (r=-0.47) and knee extensors(r=-0.46).

Similar variables were studied as a result of 2 hours treadmill load carriage in chapter 5. An additional variable was the study of torque at specific joint angles in addition to peak torque. Drift was observed for V̇O2 (68.93%). The torque curves showed significant reduction for load carriage, around the optimum muscle lengths for force (Knee extension at 180°s-1: 95°-125°, knee flexion at 180°s-1: 95°-125°) with findings supported by the peak torque values, suggesting there is no shift in muscle function. These findings were supported by associations between knee extension neuromuscular function scores, ankle plantarflexion neuromuscular function scores and energy cost variables which suggest that reductions in neuromuscular function may account for the increased energy cost.

Chapter 6 observed load carriage on repeated days. The chapter observed that energy cost did not recover to baseline 24 hours post day one (4.41%). Further increases in energy cost and V̇O2 were observed post day two for energy expenditure and V̇O2 which suggest that a cumulative increase in energy cost as a result of load carriage occurred. Knee extension at 60°s-1 and 0°s-1 was shown to not recover 24 hours post day one, these variables were shown to show increased reduction for post day two and day three. Similar findings were observed within the ankle plantarflexors but no significant changes were observed for knee flexion and ankle dorsiflexion.

Variables were also studied in a field setting during a >12hour load carriage task by Greek Special Forces soldiers. This study observed increased Medial and lateral deviations of the centre of pressure which suggests ankle instability even during unloaded walking as a result of load carriage. Large reductions were observed in vertical jump height and power as a result of the task, however this did not correlate to any biomechanical findings.