The primary goal of human locomotion is to translate the body from point A to point B, but humans must have the variability and stability to adapt and recover from constraints they may encounter. The overarching aim of this dissertation was to investigate how constraints arising from external factors (i.e., military load carriage and speed) and internal factors (i.e., hip pain) affect kinematic variability and local dynamic stability of gait. In study 1, I focus on using traditional biomechanical measures to investigate if females and males use different gait mechanics when carrying military-relevant loads, as females and males are known to use different mechanics when walking with no load. In this study, I found that females and males do use different gait mechanics when walking with military-relevant loads. Females make kinematic adaptations at the ankle and knee while males make kinematic adaptations at the hip. The differences in adaptations between females and males may be related to females’ greater risk of injury when carrying load. In study 2, I used the same cohort to investigate how military-relevant loads affect the kinematic variability and local dynamic stability of gait. I found that kinematic variability and local dynamic stability were similarly affected by load. Participants had greater kinematic variability and decreased local dynamic stability when carrying loads, which may indicate an increased risk of falling while carrying load. I also found that local dynamic stability increased with increased walking speed at all loads in the mediolateral and anteroposterior directions. However, decreased stability was detected in the vertical direction, which may require increased energy expenditure. The results of this study indicate that walking faster with increased loads may be more stable, but less energy efficient. In study 3, I investigated the how kinematic variability and local dynamic stability were affected in individuals with hip pain and a history of developmental dysplasia. I found that kinematic variability and local dynamic stability were not similarly affected in these individuals. I found that kinematic variability was greater in individuals with hip pain compared to healthy controls, but there was no difference in local dynamic stability between groups. The overall finding of this dissertation is that the relationship between kinematic variability and local dynamic stability may be dependent on the factor investigated. / 2020-07-06T00:00:00Z

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Background: Working within the military as a ground combat solider is very physically demanding. Soldiers are required to handle situations ranging from peacekeeping to counterinsurgency and combat, while faced with the task of load carriage either in form of the military gear or other additional loads. Therefore, a good aerobic and anaerobic fitness is necessary. The aerobic and anaerobic fitness can be assessed with a wide range is methods such as measuring the peak oxygen uptake (VO2peak), ventilator threshold, blood lactate concentration and heart rate. However research is rather spares regarding the effects of load carriage on the aerobic capacity. Aim: The aim of the current study was to investigate if military gear affects VO2peak, ventilatory threshold, blood lactate concentration and heart rate in ground combat soldiers. Methods: A total of eight soldiers (seven men and one woman) participated in the current study. All participants completed two biological calibrations and VO2max tests (one without and one with military gear) using a modified Bruce protocol, where VO2 (L/min), absolute and relative VO2peck (L/min and ml/kg/min respectively), heart rate (beats/min) and blood lactate concentration (mM/L) were assessed. After the completion of the tests, the soldier’s individual ventilatory threshold (VT) was visually located using the V-slope method. The Wilcoxon test was used for the not normally distributed variables (blood lactate concentration and stage when VT occurred) and the paired sample t-test for the others. The significance level was set to 0.05. Results: The results showed that the soldier had 10.6 % lower absolute VO2peak and 23.7 % lower relative VO2peak while wearing military gear compared to without (p=0.002 and p=0.001 respectively). The soldiers also had 11.8 % higher VO2 at VT with military gear (p=0.003) and reached a higher percentage of the VO2peak (p=0.023) at VT. The blood lactate concentration was significantly higher when marching at 5.4 km/h and a trend of a higher blood lactate concentration while standing was observed without military gear compared to with military gear. Conclusion: The findings from the present study shows that performing load carriage in form of the military gear significantly decreased the VO2peak. Wearing a military gear also increased the VO2 at the individual VT and made the soldier reach a higher percentage of the VO2peak at VT. These results can act as guidance when recruiting and training soldiers, along with providing important information to other professions and sports that involve load carriage.

Human movement is inherently complex, requiring the control and coordination of many neurophysiological and biomechanical degrees-of-freedom, and the extent to which individuals exhibit variation in their movement patterns is captured by the construct of motor variability (MV). MV is being used increasingly to describe movement quality and function among clinical populations and elderly individuals. However, current evidence presents conflicting views on whether increased MV offers benefits or is a hindrance to performance. To better understand the utility of MV for performance prediction, we focused on current research needs in the military domain. Dismounted soldiers, in particular, are expected to perform at a high level in complex environments and under demanding physical conditions. Hence, it is critical to understand what strategies allow soldiers to better adapt to fatigue and diverse environmental factors, and to develop predictive tools for estimating changes in soldier performance. Different aspects of performance such as motor learning, experience, and adaptability to fatigue were investigated when soldiers performed various gait tasks, and gait variability (GV) was quantified using four different types of measures (spatiotemporal, joint kinematics, detrended fluctuation analysis, and Lyapunov exponents). During a novel obstacle course task, we found that frontal plane coordination variability of the hip-knee and knee-ankle joint couples exhibited strong association with rate of learning the novel task, explaining 62% of the variance, and higher joint kinematic variability during the swing phase of baseline gait was associated with faster learning rate. In a load carriage task, GV measures were more sensitive than average gait measures in discriminating between experience and load condition: experienced cadets exhibited reduced GV (in spatiotemporal measures and joint kinematics) and lower long-term local dynamic stability at the ankle, compared to the novice group. In the final study investigating multiple measures of obstacle performance, and variables predictive of changes in performance following intense whole-body fatigue, joint kinematic variability of baseline gait explained 28-59% of the variance in individual performances changes. In summary, these results support the feasibility of anticipating and augmenting task performance based on individual motor variability. This work also provides guidelines for future research and the development of training programs specifically for improving military training, performance prediction, and performance enhancement. / Doctor of Philosophy / All people move with some level of inherent variability, even when doing the same activity, and the extent to which individuals exhibit variation in their movement patterns is captured by the construct of motor variability (MV). MV is being increasingly used to describe movement quality and function among clinical populations and elderly individuals. However, it is still unclear whether increased MV offers benefits or is a hindrance to performance. To better understand the utility of MV for performance prediction, we focused on current research needs in the military domain. Dismounted soldiers, in particular, are expected to perform at a high level in complex environments and under demanding physical conditions. Hence, it is critical to understand what strategies allow soldiers to better adapt to fatigue and diverse environmental factors, and to develop tools that might predict changes in soldier performance. Different aspects of performance were investigated, including learning a new activity, experience, and adaptability to fatigue, and gait variability was quantified through different approaches. When examining how individual learn a novel obstacle course task, we found that certain aspects of gait variability had strong associations with learning rate. In a load carriage task, variability measures were determined to be more sensitive to difference in experience level and load condition compared to typical average measures of gait. Specifically, variability increased with load, and the experienced group was less variable overall and more stable in the long term. Lastly, a subset of gait variability measures were associated with individual differences in fatigue-related changes in performance during an obstacle course. In summary, the results presented here support that it may be possible to both anticipate and enhance task performance based on individual variability. This work also provides guidelines for future research and the development of training programs specifically for improving military training, performance prediction, and performance enhancement.

Title: Appropriateness of choice to walk or run, depending on the speed of a quick relocation with load carriage Objectives: Comparison of physiological response of organism during the walk and run at speed 6 - 7,4 km.h-1 with carried load 15 kg with follow-up determination of critical speed in connection with economy of these activities where there were discovered sizes of correlation with proportional representation of fat free mass and working length of lower limb. Methods: The method applied in this research was the quantitative research based on intra-individual and inter-individual comparative analysis. Results: Based on the measured data it has been found out that there is a critical speed at 7,43 km.h-1 (±0,53), with respect to economy of walk compared to run with 15 kg load. The average heart rate during the critical speed was 129 BPM (±9,67). The average energy expenditure per minute during the critical speed was 11,9 kcal (±2,04). In addition there were discovered sizes of correlation between critical speed and the working length of lower limb where rP = 0,9203 was statiscitally significant. (α = 0,05) and between critical speed and proportional representation of fat free mass, where rP = 0,1529 was not found to be statistically significant (α = 0,05). Keywords: quick relocation, load...