Access to abstract permanently restricted to Ball State community only / Access to thesis permanently restricted to Ball State community only / School of Physical Education, Sport, and Exercise Science

Two experiments were undertaken. The objective of Experiment One was to identify the lower limb muscles that were most frequently active during the early period of a step turning task for further testing in Experiment Two. In Experiment Two participants undertook multiple trials of a step-turning task, 30 and 60° to the left and right of midline, at a self-selected pace in response to a visual cue. There were five objectives to Experiment Two. Firstly, to identify the predominant order in the onset of foot movement so that anticipatory muscle activity could be defined for this task. Secondly, to identify whether there is a consistent temporal order in movement onset between the head and the feet. Thirdly, to identify whether and how consistently anticipatory lower limb muscle activity is present bilaterally. Fourthly, to assess whether there is a consistent sequence in the onset of anticipatory muscle activity among muscles active in at least 80% of trials. The final objective was to identity whether there was a consistent temporal relationship in the onset of the anticipatory muscle activity present in at least 80% of trials, with the onset of head and foot movement. Study Design: A repeated measures design was used. Background: Anticipatory lower limb muscle activity in gait initiation and forward stepping studies has been reported to be consistently present, and associated with initial and important balance responses. Falls during turning are associated with a high incidence of hip fractures in the elderly population. The presence of anticipatory lower limb muscle activity turning has not been previously reported. Participants: There were five participants in Experiment One, and ten in Experiment Two. All were between 18 and 40 years of age and did not have neurological or musculoskeletal disorders, or severe visual loss. Results: In Experiment One, four muscles were consistently active bilaterally, during the early period of step-turning and were: tibialis anterior, gastrocnemius, biceps femoris and gluteus medius. In Experiment Two the ipsilateral foot moved before the contralateral foot in 68% of trials towards the left, and 79% of trials towards the right. The onset of head movement consistently occurred before the onset of foot movement during turns towards both directions. The percentage of trials in which the four muscles were active in an anticipatory manner was low bilaterally, ranging from 12 to 38% of trials. Objectives that involved the further analysis of muscles active in at least 80% of trials were unable to be completed. Conclusions: During a step-turning task young healthy adults predominantly move their ipsilateral foot before their contralateral foot. The consistent onset of head movement prior to that of the feet, indirectly suggests that the visual system might influence the temporal onset of the feet. The low levels of anticipatory muscle activity during step-turning suggest that the lower limbs are not involved with the initial balance responses for this task thus making it inherently different to gait initiation and forward stepping.

Tibial stress fractures are common in runners. However, it is unclear what factors are associated with tibial stress fractures. This study aimed to investigate 1) magnitudes of bone contact forces occurring while running 2) whether or not repeated application of running loads is sufficient to explain tibial stress fractures and 3) whether or not muscle fatigue alters the potential of tibial stress fractures. Tibial stress fractures were predicted through an estimation of the minimum number of cycles to failure (Nfail) using an integrated experimental and mathematical modeling approach. Short running trials within a speed range of 3.5-4 m/s of ten male runners were evaluated with a coupled force plate and 3 dimensional motion analysis system. The collected data were used to estimate joint reaction forces (JRF) and joint moments. Using these JRF and muscle forces predicted from optimization, 2-D bone contact forces at the distal end of the tibia were determined. Next, tibial stresses were estimated by applying these bone contact forces to a tibial model, which were then used to predict the Nfail. All procedures were repeated after plantarflexors fatigued from prolonged running. This study found that peaks of compressive and posterior shear forces occurred during mid stance, and these peaks equaled 8.91 ± 1.14 BW and -0.53 ± 0.16 BW, respectively. These bone contact forces led to a backward bending of the tibia during most of the stance phase and resulted in the maximum stresses of - 43.4 ± 10.3 MPa on the posterior face of the tibia. These maximum stresses predicted the group mean of Nfail as being 5.28*10⁶ cycles. However, 2.5% to 56% of population of runners have a chance of getting tibial stress fractures within 1 million cycles of a repeated foot impact. Within the context of muscle force and stress estimation procedures used in this study, Nfail appeared to increase after fatigue, not decrease as we hypothesized. / Graduation date: 2005

Access to abstract permanently restricted to Ball State community only / Access to thesis permanently restricted to Ball State community only / School of Physical Education, Sport, and Exercise Science

The purpose of this study was to compare the anabolic response to acute running exercise in two different leg muscles in endurance-trained men using two different stable isotope tracers. 6 male subjects (26±2 yr; V02max 63±2 ml•kg-' •min-') performed a 45 min treadmill run at 77±1 % intensity. Infusions of d3-leucine and d5-phenylalanine were used to measure mixed muscle FSR at rest and 24 hr post-exercise. An additional infusion of 10% amino acid solution was added to the post-exercise infusion to maximize the muscle anabolic response. Muscle biopsies were obtained from the vastus lateralis (VL) and soleus (SOL) at 2 and 6 hr of the infusion for the measurement of isotope incorporation. Additional muscle biopsies were obtained prior to and 4 hr post-exercise for determination of muscle glycogen use. At rest FSR was similar between the VL and SOL using either tracer (p>0.05). At 24 hr post-exercise FSR was elevated in both muscles, independent of the tracer used (p<0.05). Muscle glycogen was decreased to the same extent in both muscles by -31% at 4 hr post-exercise (p<0.05). These data suggest that the VL and SOL muscles are both stimulated similarly during 45 min of level grade running. Additionally, both muscles respond similarly 24 hr post-exercise, independent of the tracer used for the determination of protein synthesis. / School of Physical Education, Sport, and Exercise Science

The aim of this investigation was to compare the acute anabolic and catabolic responses of male and female vastus lateralis (VL) and soleus (SOL) muscles in response to resistance exercise (RE). Muscle biopsies from the VL of 7 males (26±3 y, 75±8 kg) and 7 females (25±3 y, 59±5 kg) were obtained before, and 2 and 6 h after 4 x 7 supine-squat, and 4 x 14 calf-press exercises at maximal effort using inertial ergometry. The mRNA levels of select myogenic (MyoD, myogenin, MRF4), proteolytic (atrogin-1 , MuRF-1), myostatin, and inflammatory (IL-6, -8, -15) genes were quantified using real-time RT-PCR. Male VL vs SOL: The SOL had higher basal mRNA levels of myogenic, proteolytic, and inflammatory genes. After exercise, the myogenic response was similar between the VL and SOL. Both muscles increased MuRF-1 similarly at 2 h, whereas 6 h post-RE proteolytic gene expression (GE) was suppressed in the VL but not in the SOL. The SOL had a reduction in myostatin GE, and a more robust inflammatory response compared to the VL. These findings indicate a more favorable growth response in the VL. Gender comparisons: VL – Basally, the male VL had higher levels of myogenic, proteolytic, myostatin, and inflammatory mRNA compared to the female VL. After exercise, both genders increased myogenic GE similarly. Both genders increased MuRF-1 initially, with females also increasing atrogin-1 and myostatin post-RE. At 6 h, males decreased proteolytic GE to below basal levels. Females also had a greater inflammatory response than males. These findings indicate a greater growth response to RE in the male VL as compared to the female VL. SOL – After exercise, both genders increased myogenic GE in the SOL, but only males increased MyoD expression. Males increased MuRF-1 mRNA but decreased myostatin GE, while females decreased atrogin-1. The inflammatory response was similar between males and females. Despite the modest differences, the net response of the female and male SOL was similar, and indicated a molecular response slightly favorable for growth. / School of Physical Education, Sport, and Exercise Science

Two experiments were undertaken. The objective of Experiment One was to identify the lower limb muscles that were most frequently active during the early period of a step turning task for further testing in Experiment Two. In Experiment Two participants undertook multiple trials of a step-turning task, 30 and 60° to the left and right of midline, at a self-selected pace in response to a visual cue. There were five objectives to Experiment Two. Firstly, to identify the predominant order in the onset of foot movement so that anticipatory muscle activity could be defined for this task. Secondly, to identify whether there is a consistent temporal order in movement onset between the head and the feet. Thirdly, to identify whether and how consistently anticipatory lower limb muscle activity is present bilaterally. Fourthly, to assess whether there is a consistent sequence in the onset of anticipatory muscle activity among muscles active in at least 80% of trials. The final objective was to identity whether there was a consistent temporal relationship in the onset of the anticipatory muscle activity present in at least 80% of trials, with the onset of head and foot movement. Study Design: A repeated measures design was used. Background: Anticipatory lower limb muscle activity in gait initiation and forward stepping studies has been reported to be consistently present, and associated with initial and important balance responses. Falls during turning are associated with a high incidence of hip fractures in the elderly population. The presence of anticipatory lower limb muscle activity turning has not been previously reported. Participants: There were five participants in Experiment One, and ten in Experiment Two. All were between 18 and 40 years of age and did not have neurological or musculoskeletal disorders, or severe visual loss. Results: In Experiment One, four muscles were consistently active bilaterally, during the early period of step-turning and were: tibialis anterior, gastrocnemius, biceps femoris and gluteus medius. In Experiment Two the ipsilateral foot moved before the contralateral foot in 68% of trials towards the left, and 79% of trials towards the right. The onset of head movement consistently occurred before the onset of foot movement during turns towards both directions. The percentage of trials in which the four muscles were active in an anticipatory manner was low bilaterally, ranging from 12 to 38% of trials. Objectives that involved the further analysis of muscles active in at least 80% of trials were unable to be completed. Conclusions: During a step-turning task young healthy adults predominantly move their ipsilateral foot before their contralateral foot. The consistent onset of head movement prior to that of the feet, indirectly suggests that the visual system might influence the temporal onset of the feet. The low levels of anticipatory muscle activity during step-turning suggest that the lower limbs are not involved with the initial balance responses for this task thus making it inherently different to gait initiation and forward stepping.