D.S. Blaise Williams

Athletes trained using stable compared to unstable surfaces exhibit distinct postural control profiles when assessed by traditional and nonlinear measures

UNLABELLED Athletes are assumed to exhibit better balance than non-athletes; however, few studies have examined the role of different types of sports on balance measures. Two athlete groups that experience divergent sport-specific balance training are stable- (i.e. basketball) and unstable-surface athletes (i.e. surfers). The purpose of this study was to quantify the effect of stable- compared to unstable-surface sports on postural stability. METHODS Eight non-athletes (NON), eight stable-surface athletes (SSA) and eight unstable-surface athletes (USA) performed five 20-s quiet standing trials while ground reaction forces were recorded. Approximate entropy (ApEn), total excursion and root mean square distances (RMS) of the center of pressure position were calculated. Univariate ANOVAs with post hoc tests were conducted for each variable. RESULTS ApEn values were lower in SSA compared to NON in the ML direction (p=0.012) and USA had lower ApEn values compared to SSA in the AP direction (p=0.036). The USA had smaller AP RMS compared to SSA (p=0.002) while the USA had greater ML RMS (p=0.008) and resultant RMS values compared to SSA (p=0.025). DISCUSSION These data suggest that USA and SSA may exhibit direction-specific differences in balance strategy due to feedback paradigm.

Increased Medial Longitudinal Arch Mobility, Lower Extremity Kinematics, and Ground Reaction Forces in High-Arched Runners

CONTEXT Runners with high medial longitudinal arch structure demonstrate unique kinematics and kinetics that may lead to running injuries. The mobility of the midfoot as measured by the change in arch height is also suspected to play a role in lower extremity function during running. The effect of arch mobility in high-arched runners is an important factor in prescribing footwear, training, and rehabilitating the running athlete after injury. OBJECTIVE To examine the effect of medial longitudinal arch mobility on running kinematics, ground reaction forces, and loading rates in high-arched runners. DESIGN Cross-sectional study. SETTING Human movement research laboratory. PATIENTS OR OTHER PARTICIPANTS A total of 104 runners were screened for arch height. Runners were then identified as having high arches if the arch height index was greater than 0.5 SD above the mean. Of the runners with high arches, 11 rigid runners with the lowest arch mobility (R) were compared with 8 mobile runners with the highest arch mobility (M). Arch mobility was determined by calculating the left arch height index in all runners. INTERVENTION(S) Three-dimensional motion analysis of running over ground. MAIN OUTCOME MEASURE(S) Rearfoot and tibial angular excursions, eversion-to-tibial internal-rotation ratio, vertical ground reaction forces, and the associated loading rates. RESULTS Runners with mobile arches exhibited decreased tibial internal-rotation excursion (mobile: 5.6° ± 2.3° versus rigid: 8.0° ± 3.0°), greater eversion-to-tibial internal-rotation ratio (mobile: 2.1 ± 0.8 versus rigid: 1.5 ± 0.5), decreased second peak vertical ground reaction force values (mobile: 2.3 ± 0.2 × body weight versus rigid: 2.4 ± 0.1 × body weight), and decreased vertical loading rate values (mobile: 55.7 ± 14.1 × body weight/s versus rigid: 65.9 ± 11.4 × body weight/s). CONCLUSIONS Based on the results of this study, it appears that runners with high arch structure but differing arch mobility exhibited differences in select lower extremity movement patterns and forces. Future authors should investigate the impact of arch mobility on running-related injuries.

A Comparison of Two Multisegment Foot Models in High- and Low-Arched Athletes

BACKGROUND Malalignment and dysfunction of the foot have been associated with an increased propensity for overuse and traumatic injury in athletes. Several multisegment foot models have been developed to investigate motions in the foot. However, it remains unknown whether the kinematics measured by different multisegment foot models are equivocal. The purpose of the present study is to examine the efficacy of two multisegment foot models in tracking aberrant foot function. METHODS Ten high-arched and ten low-arched female athletes walked and ran while ground reaction forces and three-dimensional kinematics were tracked using the Leardini and Oxford multisegment foot models. Ground reaction forces and joint angles were calculated with Visual 3D (C-Motion Inc, Germantown, MD). Repeated-measures analyses of variance were used to analyze peak eversion, time to peak eversion, and eversion excursions. RESULTS The Leardini model was more sensitive to differences in peak eversion angles than the Oxford model. However, the Oxford model detected differences in eversion excursion values that the Leardini model did not detect. CONCLUSIONS Although both models found differences in frontal plane motion between high- and low-arched athletes, the Leardini multisegment foot model is suggested to be more appropriate as it directly tracks frontal plane midfoot motion during dynamic motion.

Ankle work and dynamic joint stiffness in high- compared to low-arched athletes during a barefoot running task

UNLABELLED High- (HA) and low-arched (LA) athletes have an exaggerated risk of injury. Ankle joint stiffness is a potential underlying mechanism for the greater rate of injury within these two functionally different groups. An alternative candidate mechanism of injury in HA and LA athletes pertains to the efficacy of the foot as a rigid lever during propulsion. The purpose of this study was to quantify the differences in ankle dynamic joint stiffness, and ankle braking work and ankle propulsive work during stance phase of running. METHODS Ten HA and ten LA athletes performed five barefoot running trials while ground reaction forces and three-dimensional kinematics were recorded. Ankle dynamic joint stiffness was calculated as the slope of the ankle joint moment-ankle joint angle plot during load attenuation. Ankle braking and propulsive work values were calculated for the stance phase. RESULTS HA athletes had significantly greater ankle dynamic joint stiffness and significantly smaller ankle net and propulsive work than LA athletes. CONCLUSIONS These data demonstrate that HA and LA athletes exhibit unique biomechanical patterns during running. These patterns may be related to lower extremity injury.

Athletes who train on unstable compared to stable surfaces exhibit unique postural control strategies in response to balance perturbations

Background Athletes have been shown to exhibit better balance compared to non-athletes (NON). However, few studies have investigated how the surface on which athletes train affects the strategies adopted to maintain balance. Two distinct athlete groups who experience different types of sport-specific balance training are stable surface athletes (SSA) such as basketball players and those who train on unstable surfaces (USA) such as surfers. The purpose of this study was to investigate the effects of training surface on dynamic balance in athletes compared to NON. Methods Eight NON, eight SSA, and eight USA performed five 20-s trials in each of five experimental conditions including a static condition and four dynamic conditions in which the support surface translated in the anteroposterior (AP) or mediolateral (ML) planes using positive or negative feedback paradigms. Approximate entropy (ApEn) and root mean square distance (RMS) of the center of pressure (CoP) were calculated for the AP and ML directions. Four 3 × 5 (group × condition) repeated measures ANOVAs were used to determine significant effects of group and condition on variables of interest. Results USA exhibited smaller ApEn values than SSA in the AP signals while no significant differences were observed in the ML CoP signals. Generally, the negative feedback conditions were associated with significantly greater RMS values than the positive feedback conditions. Conclusion USA exhibit unique postural strategies compared to SSA. These unique strategies seemingly exhibit a direction-specific attribute and may be associated with divergent motor control strategies.

The Relationship Between the Use of Foot Orthoses and Knee Ligament Injury in Female Collegiate Basketball Players

BACKGROUND Anterior cruciate ligament injuries are more prevalent in female athletes than in male athletes. Basketball is a high-risk sport for anterior cruciate ligament injury in female athletes. This study was conducted to observe the effect of a foot orthosis on the knee ligament injury rate in female basketball players at one US university. METHODS One hundred fifty-five players on the womens basketball team were observed for knee ligament injury from 1992 to 2005. Athletes in the 1992-1993 to 1995-1996 school years (July-June) did not receive a foot orthosis and served as the control group; the treatment group comprised the athletes during the 1996-1997 to 2004-2005 school years (July-June). Athletes in the treatment group received a foot orthosis before participating in basketball. Data analysis included knee ligament injury rates and a comparison of injury rates with an incidence density ratio. RESULTS Athletes in the control group had three collateral ligament injuries and three anterior cruciate ligament injuries, for an injury rate of 0.50 for both the anterior cruciate ligament and collateral ligaments. Athletes in the treatment group had four collateral ligament injuries and one anterior cruciate ligament injury, for an injury rate of 0.29 for the collateral ligaments and 0.07 for the anterior cruciate ligament. Athletes in the control group were 1.72 times more likely to sustain a collateral ligament injury and 7.14 times more likely to sustain an anterior cruciate ligament injury than the treatment group. CONCLUSIONS Foot orthoses may contribute to a decreased knee ligament injury rate in female collegiate basketball players.

Arch structure is associated with unique joint work, relative joint contributions and stiffness during landing

UNLABELLED To examine lower extremity joint contributions to a landing task in high-(HA) and low-arched (LA) female athletes by quantifying vertical stiffness, joint work and relative joint contributions to landing. METHODS Twenty healthy female recreational athletes (10 HA and 10 LA) performed five barefoot drop landings from a height of 30cm. Three-dimensional kinematics (240Hz) and ground reaction forces (960Hz) were recorded simultaneously. Vertical stiffness, joint work values and relative joint work values were calculated using Visual 3D and MatLab. RESULTS HA athletes had significantly greater vertical stiffness compared to LA athletes (p=0.013). Though no differences in ankle joint work were observed (p=0.252), HA athletes had smaller magnitudes of knee (p=0.046), hip (p=0.019) and total lower extremity joint work values (p=0.016) compared to LA athletes. HA athletes had greater relative contributions of the ankle (p=0.032) and smaller relative contributions of the hip (p=0.049) compared to LA athletes. No differences in relative contributions of the knee were observed (p=0.255). CONCLUSIONS These findings demonstrate that aberrant foot structure is associated with unique contributions of lower extremity joints to load attenuation during landing. These data may provide insight into the unique injury mechanisms associated with arch height in female athletes.

High- compared to low-arched athletes exhibit smaller knee abduction moments in walking and running.

High- (HA) and low-arched athletes (LA) experience distinct injury patterns. These injuries are the result of the interaction of structure and biomechanics. A suggested mechanism of patellofemoral pain pertains to frontal plane knee moments which may be exaggerated in LA athletes. We hypothesize that LA athletes will exhibit greater peak knee abduction moments than high-arched athletes. METHODS Twenty healthy female recreational athletes (10HA and 10LA) performed five over-ground barefoot walking and five barefoot running trials at a self-selected velocity while three-dimensional kinematics and ground reaction forces were recorded. Peak knee abduction moments and time-to-peak knee abduction moments were calculated using Visual 3D. RESULTS High-arched athletes had smaller peak knee abduction moments compared to low-arched athletes during walking (KAM1: p=0.019; KAM2: p=0.015) and running (p=0.010). No differences were observed in time-to-peak knee abduction moment during walking (KAM1: p=0.360; KAM2: p=0.085) or running (p=0.359). CONCLUSIONS These findings demonstrate that foot type is associated with altered frontal plane knee kinetics which may contribute to patellofemoral pain. Future research should address the efficacy of clinical interventions including orthotics and rehabilitation programs in these athletes.

Male and female runners demonstrate different sagittal plane mechanics as a function of static hamstring flexibility

ABSTRACT Background: Injuries to runners are common. However, there are many potential contributing factors to injury. While lack of flexibility alone is commonly related to injury, there are clear differences in hamstring flexibility between males and females. Objective: To compare the effect of static hamstring length on sagittal plane mechanics between male and female runners. Method: Forty subjects (30.0±6.4 years) participated and were placed in one of 4 groups: flexible males (n=10), inflexible males (n=10), flexible females (n=10), and inflexible females (n=10). All subjects were free of injury at the time of data collection. Three-dimensional kinematics and kinetics were collected while subjects ran over ground across 2 force platforms. Sagittal plane joint angles and moments were calculated at the knee and hip and compared with a 2-way (sex X flexibility) ANOVA (α=0.05). Results: Males exhibited greater peak knee extension moment than females (M=2.80±0.47, F=2.48±0.52 Nm/kg*m, p=0.05) and inflexible runners exhibited greater peak knee extension moment than flexible runners (In=2.83±0.56, Fl=2.44±0.51 Nm/kg*m, p=0.01). For hip flexion at initial contact, a significant interaction existed (p<0.05). Flexible females (36.7±7.4º) exhibited more hip flexion than inflexible females (27.9±4.6º, p<0.01) and flexible males (30.1±9.5º, p<0.05). No differences existed for knee angle at initial contact, peak knee angle, peak hip angle, or peak hip moment. Conclusion: Hamstring flexibility results in different mechanical profiles in males and females. Flexibility in the hamstrings may result in decreased moments via active or passive tension. These differences may have implications for performance and injury in flexible female runners.

Kinematic predictors of loading during running differ by demographic group

OBJECTIVES To investigate whether previously-determined kinematic predictors of kinetics during running differ between demographic groups. PARTICIPANTS Young male (n = 13, age = 22 (2) yrs), young female (n = 13, age = 25 (4) yrs), older male (n = 13, age = 50 (4) yrs) and older female (n = 13, age = 52 (3) yrs) runners. MAIN OUTCOME MEASURES Sagittal plane kinematics and kinetics were assessed while participants ran at their preferred pace. Linear regression models were developed to predict kinetics in each group using kinematics as independent variables. RESULTS Step length was positively associated with magnitude of at least one kinetic variable in all groups. Step position was inversely associated with vertical ground reaction force variables in all groups. Step frequency and CoM excursion were also important to all groups, however direction of the associations varied. Foot angle at initial contact was important to all groups except older females. Peak knee flexion was most important to older females, but was not important to any other groups. CONCLUSION Optimal parameters for gait analysis of runners may depend on demographics of the individual. This provides insight for clinicians into the most effective evaluation and interventions strategies for different types of runners.