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Running popularity has led to a rise in chronic lower limb injuries resulting from cumulative loading. Many of these injuries are tibial stress fractures. Tibial accelerometers are commonly used to measure tibial stress and may even be predictive of injury at the distal limb. Lower body positive pressure (LBPP) treadmills have become increasingly popular amongst athletes and practitioners to prevent and treat lower limb injuries by reducing effective body weight (BW) through mechanical support. The purpose of this thesis is to investigate if BW unloading affects tibial acceleration (TA) and shock attenuation. Twelve trained distance runners (Sex: 6 males and 6 females; Age: 18-30 years) were recruited for this study. TA was measured through two Blue Trident, IMeasureU step units located at the distal tibiae. A STATSports Apex unit was also used to measure acceleration at the superior trunk and calculate shock attenuation for each limb. It was found that BW unloading had no discernable effect on mean peak TA and shock attenuation, bone stimulus, or contact time, regardless of running speed. However, a significant relationship was observed between running speed and both mean peak TA and bone stimulus where an increase in speed led to an increase in TA and bone stimulus. Furthermore, running speed did not affect shock attenuation or contact time. In conclusion, BW unloading did not alter gait kinematics in trained distance runners. / Master of Science / Running popularity has led to a rise in chronic lower limb injuries, particularly stress fractures at the shin or tibia bone, due to greater impact forces and "stiffer" landings. Tibial accelerometers are commonly used to measure these impact forces and may even be predictive of injury at the tibia bone near the ankle. The process of reducing these impact forces is called shock attenuation. Lower body positive pressure (LBPP) treadmills have become increasingly popular amongst athletes and practitioners to prevent and treat lower limb injuries by unloading body weight (BW) through mechanical support. The purpose of this thesis is to investigate if BW unloading affects tibial acceleration (TA) and shock attenuation. Twelve trained distance runners (Sex: 6 males and 6 females; Age: 18-30 years) were recruited for this study. TA was measured through two Blue Trident, IMeasureU step units located at the shin. A STATSports Apex unit was also used to measure impact at the upper trunk and calculate shock attenuation for each limb. It was found that BW unloading did not affect mean peak TA and shock attenuation, bone stimulus, or contact time, regardless of running speed. However, running speed significantly affected both mean peak TA and bone stimulus where an increase in speed led to an increase in TA and bone stimulus. Furthermore, running speed did not affect shock attenuation or contact time. In conclusion, BW unloading did not alter impact forces in trained distance runners. Caution is advised for individuals with injuries at the shin when using LBPP treadmills.

Testosterone is a steroid and anabolic hormone found in all mammals. Previous research indicates that testosterone levels correlates with physical capacities related to physical performance. However, these studies refers only to men and boys. The aim of present study was therefore to investigate the potential relationship between body composition, strength, power and endurance capabilities in relation to blood levels of testosterone and DHEAS in young female football players. Seventeen female elite football (age: 15,4 ± 0,6, body mass: 57,2 ± 7,4kg, height 1,65 ±0,04m) players volunteered for the study. Morning levels of testosterone were plotted against results of Dual-energy X-ray absorptiometry, Biodex isokinetic dynamometer, maximal counter movement jump, drop jump, 10 and 20 meters sprints and aerobic fitness (Yo-Yo intermittent endurance test). Testosterone levels were significant correlated with DHEAS as well as bone density (BMD) in L1-L4 (p <0,01) and whole body (WB) BMD (p <0,05). DHEAS also correlated with BMD in L1-L4 and WB (p <0,05). No correlations were found between testosterone, DHEAS and performance capacities. These results suggest that DHEAS predict the level of testosterone and BMD in young women. However, more research is needed to clarify the relationship between testosterone, DHEAS and physical capacities in a larger group of women.

Various models of simulated weightlessness and resulting cardiovascular effects have been researched in the last 50 years of space exploration. Examples of such models are the Alter-G (Alt-G) treadmill used for body unweighting and head-up-tilt (HUT) model each providing similar cardiovascular effects, but differing in their stimulation of vestibular centers . Advantages of using the Alt-G include: use of lower body positive pressure (LBPP) to simulate hypogravity, it acts as a countermeasure to alleviate negative cardiovascular effects of standing and provides a constant vestibular stimulus. In addition, the Alt-G shorts themselves may be providing a certain degree of LBPP, acting as a compression garment. Therefore the purpose of this study was to determine the cardiovascular effects of Alt-G shorts and how effective they are as countermeasure to deconditioning effects of space flight. This study tested cardiovascular changes in 12 men and women at 0 and 80 degrees head-up-tilt (HUT0 / HUT80) with and without Alt-G shorts using 5-lead ECG, 10-lead impedance, heart rate, systolic and diastolic blood pressure measurements at finger and arm. The tilt-induced increase in mean heart rate (HR) was significantly smaller when subjects wore the Alt-G shorts. Shorts ended up reducing HR by 2.3 bpm in supine control and by 6.7 bpm at HUT80 (p0.05. Other cardiovascular variables did not show any significant effect from shorts. In conclusion, this study was in line with results from other studies that used compression garments to determine cardiovascular effects of LBPP.

At any given running speed, weight support with a lower body positive pressure (LBPP) device (i.e. Alter-G treadmill) reduces V̇O2. However, it is unknown how application of LBPP during running impacts lactate metabolism, specifically lactate threshold. Purpose: To determine if body weight unloading with the Alter-G treadmill alters lactate threshold. Methods. Maximal aerobic capacity (V̇O2max) and lactate threshold (LT) was determined in 8 male subjects on an Alter-G treadmill at 100% and 80% body weight loading at 0% grade in a randomized crossover design. V̇O2max tests started at 7 mile h-1 and increase speed by 1 mile h-1 every 2 min till voluntary exhaustion and were separated by a minimum of 7 days. LT tests started at 5 mile h-1 and increased speed to 6, 7, 7.5, 8.0, 8.5, 9.0 (additional stages increase speed by 0.5 mile h-1) every 3 min until the subject reached ¡Ö85% of V̇O2max. LT tests were separated by a minimum 3 days. V̇O2, heart rate (HR), mean arterial blood pressure (MAP) and changes in Hct, [Hb], and total protein ([TP]) were determined on separate days in a randomized crossover design. Plasma lactate concentrations were determined from venous blood samples (4 ml) obtained at rest and during the last minute of each exercise stage. Lactate threshold was determined from a log-log plot of lactate concentration (mM) and relative V̇O2 (ml O2 min-1 kg-1 BM). Results. V̇O2max determined during running at 100% and 80% loading were similar (52.3 ± 0.9 and 52.7 ± 0.7 ml O2 min-1 kg-1 BM, respectively). The energy cost of running at 9 mile h-1 (all subjects completed stages between 5 and 9 mile h-1) was reduced by 12% at 80% body weight (37.2 ± 2.9 ml O2 min-1 kg-1 BM) compared to running at 100% body weight (42.3 ± 1.7 ml O2 min-1 kg-1 BM, <0.05). However, plasma lactate at 9 mile h-1 was similar during 80% and 100% body weight running (3.4 ± 0.4 and 3.1 ± 0.7 mM, respectively). Plasma lactate at a given V̇O2 was higher (p < 0.05) while running at 80% body weight compared to 100% body weight running. Calculated LT at 100% BW loading (36.3 ± 1.3 ml O2 min-1 kg-1 BM) was higher than 80% BW loading (32.2 ± 1.8 ml O2 min-1 kg-1 BM, p<0.05). During running at 80% BW HR was reduced compared to 100% BW running (p<0.05) however the MAP response was similar. During exercise the reduction in PV, at any given V̇O2 was larger at 80% BW compared to 100% BW running (p<0.001). Conclusion. During running, BW unloading with LBPP decreased the energy cost of exercise but not lactate levels. Body weight unloading caused a lowering of the LT. The reduction in whole body energy cost was not associated with a reduction in the lactate production since plasma lactate accumulation at a given speed was similar with and without LBPP.

More than one-half of university students in the United States and Canada are not active enough to gain health benefits. Enjoyment of exercise proposes a feasible solution to the absence of motivation surrounding physical activity. The purpose of this study is to compare the differences in reported enjoyment between upper and lower body cycling graded exercise to exhaustion (GXT). Seven university students (23 ± 3 years old; 26 ± 4 kg/m2) performed two randomized graded exercise tests on different days: one for upper body, one for lower body. Feeling Scale (FS) measured the affective response during exercise. Post-exercise enjoyment values were recorded 15 minutes after concluding GXT using the Physical Activity Enjoyment Scale (PACES), which has been shown to be a valid and reliable measure of physical activity enjoyment. Paired t-tests were used to evaluate mean differences between upper and lower body GXT enjoyment scores. Rank biserial correlations and Cohen's d values were used to evaluate effect size for the non-parametric and parametric analyses. Alpha level was set a priori at p < 0.05. Means and standard deviations were calculated for PACES, age, and BMI. No significant differences were found for enjoyment (p=0.162) between upper (104.3 ± 12.6) and lower-body cycling (97.8 ± 15.3). Notable effect sizes were found for the PACES Total and several subscales (Enjoy/Hate, Pleasant, and Contentment). No significant differences were found for the FS at ventilatory threshold (p=0.586) or at maximal aerobic power (p=0.670) between the upper and lower body GXT trials. More research is needed to explore exercise enjoyment across different exercise modes and provide a more particular evaluation of PACES subscales. Further research should aim to compare enjoyment levels across different physical activity levels (e.g., low, moderate, high), between sexes and within diverse populations.

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