Inledning: 70% av alla skador av det främre korsbandet (ACL) sker vid icke-kontakt-situationer. En låg kokontraktionsratio mellan hamstrings och quadriceps (H:Q) kan ses som en riskfaktor för ACL. Få studier är gjorda kring detta i samband med enbenslandningar på olika underlag. Syfte: Syftet med studien var att undersöka kokontraktionen mellan rektus femoris och biceps femoris samt ground reaction force (GRF) vid drop landing från 30 cm på stabilt respektive instabilt underlag. Metod: Tre män deltog i studien. Studien utfördes i ett rörelselabb där deltagarna utförde enbenslandningar på stabilt respektive instabilt underlag. Muskelaktivitet mättes med elektromyografi (EMG) i musklerna rektus femoris och biceps femoris. GRF mättes med kraftplatta. EMG-amplituden beräknades i relation till respektive deltagares maximum voluntary isometric contraction (MVIC). Medelvärde och standardavvikelse för respektive muskel, H:Q-kokontraktionsratio och högsta uppmätta GRF (N/kg) beräknades. Resultat: EMG visade en högre aktivitet i rektus femoris jämfört med biceps femoris vid landning på respektive underlag. På gruppnivå visade biceps femoris minskad aktivitet vid landning på instabilt underlag och H:Q-kokontraktionsration minskade. Högsta uppmätta GRF visade en tendens att minska vid landning på instabilt underlag. Konklusion: Den minskade aktiviteten i biceps femoris vid instabilt underlag var oväntad vilket eventuellt kan förklaras med det låga deltagarantalet, den interindividuella variationen och val av underlag. Mer forskning behövs med ett större urval för att få ett mer tillförlitligt resultat. Det vore även intressant att standardisera och mäta knäledsvinkeln och inkludera mer utmanande instabila underlag. Detta skulle kunna bidra till ökade kunskaper kring olika underlag vid preventions- och rehabiliteringsträning.

The prevalence of asymmetry in performance research has increased in recent years with mixed results. Much of the performance research has focused on unilateral jumping activities attempting to show relationships to other performance variables. However, bilateral ground reaction forces (bGRF) from jumps are more frequently assessed in athlete monitoring programs and the asymmetry from those jumps could be a simple addition to data already being collected. Research into bGRF asymmetries is lacking and no studies have addressed longitudinal changes. Additionally, research into the relationship of asymmetries to performance have infrequently used athletes. For these reasons, this dissertation will focus on bGRFs by assessing reliability, determining the relationship to performance, and tracking longitudinal changes among collegiate athletes. These data indicate that impulse has high absolute (ICC > 0.87) and relative (CV < 3.22) reliability values and should be the preferred metric for assessing jumping asymmetry. As well, a combination of the braking and propulsive phase above body mass has higher correlations (r = -0.25 to -0.49) to jumping performance compared to the propulsive phase alone (r = -0.09 to 0.26). Males and female soccer players have differing relationships with asymmetry as males had the greatest correlations between weighted countermovement jump (CMJ) asymmetry and weighted CMJ performance (r = -0.49), whereas females produced their greatest correlations with unweighted CMJs (r = -0.43). Additionally, all statistically significant correlations between asymmetry and performance were negative. Athletes with higher asymmetry values typically realize improvements over time without specific interventions, whereas athletes with lower values may not experience many fluctuations. Overall, asymmetry has negligible relationships to strength lev els (r = 0.30 to with strength training. 0.22) but seems to be associated with the improved motor coordination Indeed, athletes with higher asymmetry values involved even displayed trends of greater performance gains over time.

The purpose of this study was to determine the acute effects of heavy resistance exercise on agility performance in court-sport athletes. Five men (age: 20.6 ± 1.9 years; body mass: 79.36 ± 11.74 kg; body height: 1.93 ± 0.09 m) and five women (age 21.2 ± 2.7 years; body mass: 65.8 ± 10.18 kg; body height 1.77 ± 0.08 m) volunteered to participate in the present study. All subjects were NCAA Division II athletes who currently participated in tennis or basketball and all had previous resistance training experience of at least one year. In a counterbalanced design, agility performance during a 10 m shuttle test was assessed following either a dynamic warm-up (DW) or heavy resistance warm-up (HRW) protocol. The HRW protocol consisted of three sets of squats at 50, 60, and 90% of 1-RM. Agility performance was captured using an eight camera motion analysis system and the mechanical variables of stride length, stride frequency, stance time, flight time, average ground reaction force, as well as agility time were recorded. No significant differences were reported for the HRW and DW protocols for any of the mechanical variables (p>0.05), although there was a trend towards the HRW protocol producing faster agility times compared to the control protocol (p = 0.074). Based on the trend towards a significant effect, as well as individual results it is possible that HRW protocols could be used as an acute method to improve agility performance in some court-sport athletes.

The purpose of this study was to determine the acute effects of heavy resistance exercise on agility performance in court-sport athletes. Five men (age: 20.6 ± 1.9 years; body mass: 79.36 ± 11.74 kg; body height: 1.93 ± 0.09 m) and five women (age 21.2 ± 2.7 years; body mass: 65.8 ± 10.18 kg; body height 1.77 ± 0.08 m) volunteered to participate in the present study. All subjects were NCAA Division II athletes who currently participated in tennis or basketball and all had previous resistance training experience of at least one year. In a counterbalanced design, agility performance during a 10 m shuttle test was assessed following either a dynamic warm-up (DW) or heavy resistance warm-up (HRW) protocol. The HRW protocol consisted of three sets of squats at 50, 60, and 90% of 1-RM. Agility performance was captured using an eight camera motion analysis system and the mechanical variables of stride length, stride frequency, stance time, flight time, average ground reaction force, as well as agility time were recorded. No significant differences were reported for the HRW and DW protocols for any of the mechanical variables (p>0.05), although there was a trend towards the HRW protocol producing faster agility times compared to the control protocol (p = 0.074). Based on the trend towards a significant effect, as well as individual results it is possible that HRW protocols could be used as an acute method to improve agility performance in some court-sport athletes.

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The unprecedented growth in participation in collegiate athletics has been accompanied by an increase in injury burden. The complex and multifactorial nature of sports injuries highlights the importance of monitoring athletes prospectively using a novel and holistic biopsychosocial approach, as opposed to contemporary practices that silo these facets of health. Data collected over two competitive, basketball seasons were used in a principal component analysis (PCA) model with the following objectives: i) Determine if on-court, sensor-derived and force-plate-derived countermovement jump (CMJ) biomechanics were correlated, ii) determine the reliability of the biomechanical principal components (PCs) and psychological state metrics (e.g., self-reported pain, etc.) across five preseason weeks, iii) investigate whether biomechanical PCs were correlated with psychological state across a season, and iv) explore whether subject-specific meaningful fluctuations could be detected using minimum detectable change statistics. Weekly CMJ (force plates) and on-court data (inertial measurement units), as well as psychological state (questionnaire) data were collected on the women’s basketball team at McMaster University for two seasons. It was found that on-court and CMJ biomechanics were correlated both between and within systems (r = |0.10, 0.94|; p < 0.05), suggesting that PCA would be an effective method to summarize data. The derived PCs displayed excellent reliability (ICC > 0.9), while psychological state metrics displayed moderate-to-good reliability (ICC = 0.71 – 0.89). While many relationships (n = 27) were identified between biomechanical PCs and psychological state metrics, no overarching associations were identified at the group level. However, subject-specific relationships were identified in case-studies, highlighting the potential utility of “red-flagging” meaningful fluctuations from normative biomechanical and psychological patterns. Overall, this work demonstrates the potential of advanced analytical modeling to characterize components of student-athlete performance, health, and well-being, and the need for more tailored and patient-centered athletic monitoring practices. / Thesis / Master of Science (MSc)

Adolescent idiopathic scoliosis (AIS) is characterized by a three-dimensional curve within the spine thus creating asymmetries within the trunk. In addition to modifying the trunk geometry, these structural asymmetries change the location of the center of mass. Gait patterns in people with AIS may possibly be altered on the basis of these structural changes. The purpose of this study was to identify differences in gait kinematics and kinetics as well as left-right symmetry as a function of the severity of adolescent idiopathic scoliosis. Forty-five girls divided into a control group, a mild-to-moderate AIS group and a severe AIS group participated in data collection. Gait analysis included bilateral kinematic and kinetic measurements. The maximal joint ranges of motion at the ankle, knee, hip and trunk-pelvis were analyzed. Maxima and minima in the antero-posterior, medio-lateral and vertical components of ground reaction force (GRF) were compared between the three groups as well as the median frequencies obtained from a frequency spectrum analysis of GRF. A symmetry index was computed between the primary curve side and the contralateral side for each kinematic and kinetic variable. Both AIS groups differed from controls in their range of motion at the ankle and at the knee but for the AIS group with severe curves, this was also observed at the hip. Both local maxima in the vertical component and the maximum of the antero-posterior component of the ground reaction force were decreased while the local minimum of the vertical component and the antero-posterior component of GRF increased in the severe AIS group compared to the control group. Higher median frequency contents in the antero-posterior and vertical component of ground reaction force were found in the AIS groups than in controls. No difference in asymmetry was found in any of the variables between all groups. These results seem to indicate that severe AIS participants have a more altered gait pattern than the mild-to-moderate AIS group. Findings from this study point toward greater changes in kinematics and kinetics during stance between all AIS groups and the control group.

Context: Abdominal training may decrease the risk of lower extremity injuries through improved balance and postural control. Objective: To determine the effect of an eight-week abdominal-training program on center of pressure, lower extremity joint angles, and abdominal muscle activation during a single-leg drop landing. The effects of abdominal training on abdominal muscle thickness was assessed. Design: A cohort research design. Setting: Research laboratory. Other Participants: Sixty healthy physically active college-aged students participated. They were divided into three groups: Control, Chronic ankle instability (CAI), and Healthy. Nineteen Control (age = 22.0 ± 2.72 yrs, mass = 74.1 ± 13.8 kg, height = 172.6 ± 11.3 cm, BMI = 24.8 ± 3.1 %), 21 CAI (age = 22.1 ± 2.3 yrs, mass = 77.6 ± 14.0 kg, height = 175.4 ± 12.3 cm, BMI = 25.1 ± 2.6 %), and 20 healthy (age = 22.9 ± 3.4 yrs, mass = 70.9 ± 15.6 kg, height = 172.2 ± 8.9 cm, BMI = 23.7 ± 3.3 %). Subjects in the CAI group had a history of CAI and functional ankle instability (FAI). The Ankle Instability Index and the Functional Ankle Ability Measure were used to self-report CAI and FAI respectively. Interventions: The CAI and Healthy groups participated in an eight-week abdominal-training program while the Control group maintained their normal activities of daily living and level of physical activity. Main Outcome Measures: Abdominal muscle thickness was measured biweekly throughout the study. Center of pressure excursion, muscle activation, vertical ground reaction force, and lower extremity joint angles were measured during a single-leg drop landing, pre- and postabdominal training. Results: Muscle thickness at rest increased in the rectus abdominis and external oblique muscles follow training. Eight weeks of abdominal training decreased vertical ground reaction forces and muscle activation down the lower kinetic chain. Center of pressure excursion and velocity were increased following training. Conclusions: Eight-weeks of abdominal training increased abdominal muscle thickness. Training improved neuromuscular efficiency throughout the kinetic chain and may have improved dynamic postural control. Our data also suggest CAI subjects may utilize both feedforward and feedback mechanisms to maintain postural control.

The relationship between asymmetry and performance is still undetermined in the literature. Methods of assessing asymmetry have been inconsistent and focused on the analysis of jumping asymmetry. Dual ground reaction forces are prevalent in athlete monitoring, though underutilized in asymmetry research. The purpose of this study was to assess the relationship of countermovement jump (CMJ) impulse asymmetry to performance in collegiate soccer athletes. Male and female athletes were selected from an ongoing athlete research repository database of NCAA D-I soccer athletes. All athletes contributed two maximal effort unweighted (CMJ0) and weighted countermovement jumps (CMJ20) using the mean for calculations. Propulsive phase asymmetry scores (PrPAS) and positive impulse asymmetry scores (PIAS) were calculated to determine the magnitude of asymmetry for each prospective phase. Statistically significant correlations were found between CMJ0 jump height and unweighted PIAS ( = -0.43) in females. Males had statistically significant correlations between CMJ20 jump height and weighted PIAS ( = -0.49). Neither unweighted PrPAS nor weighted PrPAS produced statistically significant correlations ( < 0.26) to their prospective jump heights. When assessing CMJ asymmetry, it is recommended to conduct both weighted and unweighted CMJ testing, utilizing PIAS as the metric to be assessed.

M.S. / Electronics, wearable devices are important in nowadays informationalized lifestyle. One prominent problem with those electronic devices is that almost all of them depend on batteries as power sources, which has become a bottleneck due to the limited life span. Constantly replacing or recharging batteries is inconvenient, burdensome, and sometimes even impossible. This problem is more intractable when the power cannot be accessed conveniently (such as during fieldwork, hiking, and military missions). What’s more, no matter how much energy the battery stores, it will drain eventually. In addition, large battery will add extra weight and occupy space. Substitute power supply that conquer these aforementioned dilemmas are thus highly desirable. Energy harvesting by its nature could be an inexhaustible replacement for batteries. This insight inspires so many energy harvesting researchers tirelessly working and trying to make it happen. Suspended backpack is an effective way to harvest energy from human motions.This study evaluates different energy harvesting backpack configurations and comprehensively assessed the power generation, dynamic interaction and human comfort. Dynamic modelling considering the dynamic interaction between human body and backpack is established to optimize the design. Bench tests and treadmill tests are carried out to evaluate the real performance. Experimental results show that the harvesting energy from human motion via a suspended energy-harvesting backpack could incessantly generate considerable electricity applicable for charging carry-on electronic devices. The potential application scenarios of this technology include solders, field-workers as well as outdoor adventure.