Context: There has been recent speculation that the intrinsic muscles of the foot may play a larger role in lower extremity control and injury than previously believed. Multiple studies have shown that certain intrinsic muscles increase in size and strength after transitioning to minimalist shoe running, theoretically decreasing injury risk. There are currently no studies that examine the effect that training barefoot has in other athletic populations. Objective: Our purpose was to compare the intrinsic and extrinsic foot muscle size and strength in gymnasts (who predominantly train barefoot) and cheerleaders (who predominantly train shod). Another purpose was to measure time to stability for both groups shod and unshod. Design: Observational study. Setting: Human Performance Laboratory. Participants: 16 collegiate gymnasts (height = 159.3 ± 4.9cm, weight = 56.7 ± 4.3kg) and 16 collegiate cheerleaders (height = 161.9 ± 5.4cm, weight = 58.7 ± 7.1kg) volunteered for this study. Main Outcome Measure(s): The muscle size of 6 intrinsic and extrinsic muscles of the foot were measured using ultrasound, toe flexor strength, as assessed using a custom-made dynamometer, and time to stability following a drop landing, as assessed using ground reaction force data collected with force plates. Results: There were no significant group differences in great toe flexor strength (p = 0.274), lateral toe flexor strength (p = 0.824), or any of the time to stability conditions (p = 0.086 – 0.90). Only one muscle, fibularis longus, was significantly bigger in gymnasts than cheerleaders (p = 0.017) Conclusions: Our findings suggest that the barefoot training of gymnasts may not have as large of an impact on the foot musculature and strength as running barefoot or in minimalist shoes has on these factors.

The purpose of this investigation was to explore the phenotypic and performance outcomes associated with ACTN3 and ACE polymorphisms. Ten trained men (age = 25.8 ± 3.0 years, height = 183.3 ± 4.1 cm, body mass = 92.3 ± 9.3 kg, and back squat to body mass ratio = 1.8 ± 0.3) participated. Blood samples were analyzed to determine ACTN3 and ACE polymorphisms. Standing ultrasonography images of the vastus lateralis (VL) were collected to determine whole muscle cross-sectional area (CSA-M), and a percutaneous muscle biopsy of the VL was collected to determine type I–specific CSA (CSA-T1), type II–specific CSA (CSA-T2), and type II to type I CSA ratio (CSA-R). Isometric squats were performed on force platforms with data used to determine peak force (IPF), allometrically scaled peak force (IPFa), and rate of force development (RFD) at various timepoints. One repetition maximum back squats were performed, whereby allometrically scaled dynamic strength (DSa) was determined. Cohen's d effect sizes revealed ACTN3 RR and ACE DD tended to result in greater CSA-M but differ in how they contribute to performance. ACTN3 RR's influence seems to be in the type II fibers, altering maximal strength, and ACE DD may influence RFD capabilities through a favorable CSA-R. Although the findings of the current investigation are limited by the sample size, the findings demonstrate the potential influence of ACTN3 and ACE polymorphisms on isometric and dynamic strength testing. This study may serve as a framework to generate hypotheses regarding the effect of genetics on performance.

PURPOSE: The purpose of the study was to examine the relationships between muscle cross-sectional area (CSA) measured by either ultrasonography or biopsy and measures of isometric peak force (IPF) and rate of force development (RFD). METHODS: Fifteen well-trained males (IPF=4445.467 + 613.690 N) participated in the study. Prior to testing and following an overnight fast, each subject’s vastus lateralis (VL) was measured for anatomical CSA (ACSA) using ultrasonography. A muscle biopsy was also sampled from the VL of each subject immediately after the ACSA measurement and at the same site on the VL. Fiber CSA (FCSA) was assessed using immunofluorescent techniques. IPF and RFD at 0-50ms, 0-100ms, 0-150ms, and 0-200ms were assessed during an isometric mid-thigh pull test on force platforms sampling at 1000Hz. Pearson product-moment correlations were calculated between muscle sizes and performance. Statistical significance was set as p≤0.050. RESULTS: Statistically significant correlations were observed between Type II FCSA and IPF (r=0.774, p<0.001), RFD150 (r=0.661, p=0.007), and RFD200 (r=0.725, p=0.002). ACSA was only significantly associated with IPF (r=0.596, p=0.019). Type I FCSA did not relate to any performance measures. CONCLUSIONS: It is clear from our results and previous literature that ultrasonography and muscle biopsy data provide relevant information regarding muscle size and performance. However, the discrepancies observed in the current study between the two suggest each is providing slightly different information to researchers. Specifically, Type II FCSA might be superior when considering more sensitive performance measurements such as RFD.

The main aim of this thesis was to examine hamstrings anatomy and its influence on knee flexor muscle function in healthy young men. A secondary aim was to better understand the implications of hamstrings anatomy and function, and their variability, in relation to the risk of strain injury. The functional and conventional H:Q ratios (examined up to high angular velocities) as well as the knee joint angle-specific isometric H:Q ratio exhibited good test-retest reliability at joint positions that closely replicated the conditions of high injury risk. Football players did not exhibit any differences in angle-specific or peak torque H:Q ratios compared to recreationally active controls. Knee extensor and flexor strength, relative to body mass, of footballers and controls was similar for all velocities, except concentric knee flexor strength at 400° s-1 (footballers +40%; P < 0.01). Muscle volume explained 30-71% and 38-58% of the differences between individuals in knee extensors and flexors torque respectively across a range of velocities. A moderate correlation was also found between the volume of these antagonistic muscle groups (R2= 0.41). The relative volume of the knee extensors and flexors explained ~20% of the variance in the isometric H:Q ratio and ~31% in the high velocity functional H:Q ratio. Biceps femoris long head exhibited a balanced myosin heavy chain isoform distribution (47.1% type I and 52.9 % total type II) in young healthy men, while BFlh muscle composition was not related to any measure of knee flexor maximal or explosive strength. Biceps femoris long head proximal aponeurosis area varied considerably between participants (>4-fold) and was not related to biceps femoris long head maximal anatomical cross-sectional area (r= 0.04, P= 0.83). Consequently, the aponeurosis:muscle area ratio exhibited 6-fold variability (range, 0.53 to 3.09; CV= 32.5%). Aponeurosis size was not related to isometric or eccentric knee flexion strength. The findings of this thesis suggest that the main anatomical factor that contributes to knee flexors function in vivo is hamstrings muscle size, while muscle composition and aponeurosis size do not seem to have a significant influence. The high inter-individual variability of the biceps femoris long head proximal aponeurosis size suggests that a disproportionately small aponeurosis may be a risk factor for strain injury. In contrast, biceps femoris long head muscle composition does not seem to explain the high incidence of strain injuries in this muscle. Quadriceps and hamstrings muscle size imbalances contribute to functional imbalances that may predispose to strain injury and correction of any size imbalance may be a useful injury prevention tool. Finally, regular exposure to football training and match-play does not seem to influence the balance of muscle strength around the knee joint.

Key words: lumbar stabilization exercise, multifidus muscle size, low back pain. Low back pain is one of the most common conditions in mankind. Therefore, it is needed an exact diagnostic and the most effective problem solving method. There is an evidence of dysfunction in deep lower back and abdominal muscles in low back pain patients. Accordingly, the aim of this study was to define the influence of lumbar stabilization exercise for chronic low back pain, and to examine L4- L5 multifidus and transversus abdominis muscles size. The objectives of our study: to determine and compare normal and chronic low back pain patients ranges of L4- L5 multifidus and transversus abdominis muscles size; to evaluate deep lower back and abdominal muscles function before and after lumbar stabilization exercise; to estimate chronic low back pain changes duaring stabilization exercise. The methods of our research: ultrasound imaging, the instrument of pressure bio- feedback „Stabilizer“, Oswestry Low Back Pain Disability Index Questionnaire, the analysis of mathematical statistics. This work consists of two studies with different participants. 16 healthy individuals and 16 chronic low back pain patients were studied in ultrasound imaging measurement. 12 chronic low back pain patients (4 women and 8 men) were participated in lumbar stabilization exercise program. Results: L4- L5 multifidus muscle size was larger (27 %) in males than in females, transversus abdominis muscle size was larger (17... [to full text]

The broad aim of this thesis was to progress understanding of the neuromechanics of joint stability and injury mechanisms by investigating the interactions between neuromuscular function and balance perturbations as well as the influence of sex and fatigue on these variables. Knee extensor (KE) and plantar flexor (PF) isometric strength parameters (maximum voluntary torque (MVT), explosive voluntary torque (EVT)) were related in young healthy adults. EVT of KE and PF were correlated at 4/5 time points during the rising torque-time curve for all absolute (r = 0.488-0.755) and relative (to body mass (BM) (r = 0.517-0.669) and MVT (r = 0.353-0.480)) expressions of EVT. These results suggest that KE and PF function is related for both maximum and explosive torque. Males were stronger for KE (+89%) and PF (+55%) than females. Males also displayed greater EVT at all time points in KE (+57-109%) and at 50-150 ms in PF (+33-52%). When MVT and EVT were normalised to BM, males continued to be stronger at all time points in KE (+23-60%) and from 100-150 ms (18-20%) in PF. No sex differences were found when EVT was normalised to MVT. Furthermore, sex differences were discovered in muscle morphology. Females had a smaller knee flexor (KF):KE size ratio, a proportionately small sartorius (SA) and gracilis (GR) and a proportionately larger vastus lateralis (VL), potentially predisposing females to greater risk of ACL injury. Females had a larger biceps femoris long head (BFlh) as a proportion of the KF than males, which may contribute to the higher risk of hamstring strain injury (HSI) in males. Regarding explosive performance and perturbation response, explosive PF torque had a weak to moderate correlation with COM displacement (COMD) from 400-500 ms (r = -0.346 to -0.508) and COM velocity (COMV) from 300-500 ms (r = -0.349 to -0.416), with weaker correlations between explosive KE torque and COMV at 400 ms (r = -0.381 to -0.411) but not with COMD. These findings suggest that greater explosive torque results in better control of the COM in response to unexpected perturbations. The effects of football simulated fatigue on these factors resulted in reduced maximal KF and KE torque. However, football simulated fatigue was not found to reduce EVT of either muscle group, or explosive H/Q ratio. Football simulated fatigue resulted in impaired balance response to unexpected perturbation in the posterior but not the anterior direction.

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