Jason C. Gillette

Effects of stride length and running mileage on a probabilistic stress fracture model.

UNLABELLED The fatigue life of bone is inversely related to strain magnitude. Decreasing stride length is a potential mechanism of strain reduction during running. If stride length is decreased, the number of loading cycles will increase for a given mileage. It is unclear if increased loading cycles are detrimental to skeletal health despite reductions in strain. PURPOSE To determine the effects of stride length and running mileage on the probability of tibial stress fracture. METHODS Ten male subjects ran overground at their preferred running velocity during two conditions: preferred stride length and 10% reduction in preferred stride length. Force platform and kinematic data were collected concurrently. A combination of experimental and musculoskeletal modeling techniques was used to determine joint contact forces acting on the distal tibia. Peak instantaneous joint contact forces served as inputs to a finite element model to estimate tibial strains during stance. Stress fracture probability for stride length conditions and three running mileages (3, 5, and 7 miles x d(-1)) were determined using a probabilistic model of bone damage, repair, and adaptation. Differences in stress fracture probability were compared between conditions using a 2 x 3 repeated-measures ANOVA. RESULTS The main effects of stride length (P = 0.017) and running mileage (P = 0.001) were significant. Reducing stride length decreased the probability of stress fracture by 3% to 6%. Increasing running mileage increased the probability of stress fracture by 4% to 10%. CONCLUSIONS Results suggest that strain magnitude plays a more important role in stress fracture development than the total number of loading cycles. Runners wishing to decrease their probability for tibial stress fracture may benefit from a 10% reduction in stride length.

Gait analysis post anterior cruciate ligament reconstruction: Knee osteoarthritis perspective

Individuals with anterior cruciate ligament (ACL) reconstruction are at increased risk to develop knee osteoarthritis (OA). Gait analysis describing kinetics of the lower extremity during walking and stair use (stair ascent and stair descent) can provide insight to everyday dynamic knee joint loading. In this study, we compared lower extremity gait patterns of those with ACL reconstruction (>1 year) to a control group. Fifteen ACL reconstructed individuals and 17 healthy controls participated in this study. Knee extensor and flexor strength were assessed. Using inverse dynamics, lower extremity moments were calculated during the stance phase of walking and during two steps of stair ascent and descent. Univariate ANOVA was used to test for main effects between (1) injured leg and control group and (2) non-injured leg and control group. Student paired t-tests were used to determine differences between the injured and non-injured leg. Those with ACL reconstruction exhibited reduced initial knee flexion angles during stair descent, reduced knee extension moments during stair descent and stair ascent (second step), and increased hip extension moments during stair ascent (second step) and walking as compared to controls. Knee flexor strength was significantly reduced in the ACL group, but no differences were found in knee extensor strength. No kinematic or kinetic differences were observed between the injured and non-injured leg of the ACL group. Walking and stair ambulation highlight altered joint loading in those with ACL reconstruction surgery. Individuals appeared to compensate for lower knee extension moments by increasing hip extension moments. Furthermore, the load distribution on the articular cartilage is likely shifted as evidenced by reduced knee flexion angles in the ACL reconstructed leg.

Internal femoral forces and moments during running: Implications for stress fracture development

BACKGROUND Femoral stress fractures tend to occur at the neck, medial proximal-shaft, and distal-shaft. The purpose of this study was to determine the internal femoral forces and moments during running. It was expected that larger loads would occur at these common sites of femoral stress fracture. METHODS Ten subjects ran at their preferred running speed over a force platform while motion capture data were collected. Static optimization in conjunction with a SIMM musculoskeletal model was used to determine individual muscle forces of the lower extremity. Joint contact forces were determined, and a quasi-static approach was used to calculate internal forces and moments along a centroid path through the femur. FINDINGS The largest mean peak loads were observed at the following regions: anterior-posterior shear, 7.47 bodyweights (BW) at the distal-shaft (posteriorly directed); axial force, 11.40BW at the distal-shaft (compression); medial-lateral shear, 3.75BW at the neck (medially directed); anterior-posterior moment, 0.42BWm at the proximal-shaft (medial surface compression); torsional moment, 0.20BWm at the distal-shaft (external rotation); medial-lateral moment, 0.44BWm at the distal-shaft (anterior surface compression). INTERPRETATION The mechanical loading environment of the femur during running appears to explain well the redundancy in femoral stress fracture location. We observed the largest internal loads at the three femoral sites prone to stress fracture.

Effects of running speed on a probabilistic stress fracture model.

BACKGROUND Stress fractures are dependent on both loading magnitude and loading exposure. Decreasing speed is a potential mechanism of strain reduction during running. However, if running speed is decreased the number of loading cycles will increase for a given mileage. It is unclear if these increased loading cycles are detrimental despite reductions in bone strain. The purpose of this study was to determine the effects of running speed on the probability of tibial stress fracture during a new running regimen. METHODS Ten male subjects ran overground at 2.5, 3.5, and 4.5m/s. Force platform and kinematic data were collected synchronously. Inverse dynamics and musculoskeletal modeling were used to determine joint contact forces acting on the distal tibia. Peak tibial contact force served as input to a finite element model to estimate tibial strains. Stress fracture probability for each running speed was determined using a probabilistic model based on published relationships of bone damage, repair, and adaptation. The effects of speed on stress fracture probability was compared using a repeated measures ANOVA. FINDINGS Decreasing running speed from 4.5 to 3.5m/s reduced the estimated likelihood for stress fracture by 7% (P=0.017). Decreasing running speed from 3.5 to 2.5m/s further reduced the likelihood for stress fracture by 10% (P<0.001). INTERPRETATION Runners wanting to reduce their risk for tibial stress fracture may benefit from a decrease in running speed. For the speeds and mileage relative to the current study, stress fracture development was more dependent on loading magnitude rather than loading exposure.

Using electrical stimulation to control standing posture

Describes strategies that have been used to control standing posture with electrical stimulation and reviews research efforts aimed at improving the performance of stimulation systems.

The effects of symmetric and asymmetric foot placements on sit-to-stand joint moments

The purpose of this study was to determine the effects of symmetric and asymmetric foot placements on joint moments during sit-to-stand movements. Three symmetric (foot-neutral, foot-back, and foot-intermediate) and three asymmetric foot placements (preferred stagger, nonpreferred stagger, and intermediate stagger) were tested. Standard (46 cm) and low (41 cm) seat heights were chosen to represent an average public seat height and a 10% lower seat height. Using inverse dynamics, maximum ankle plantarflexion, knee extension, hip extension, and hip abduction moments were calculated. Hip extension moments were significantly increased when using foot-neutral as compared to foot-back. Ankle plantarflexion and knee extension moments were significantly increased when a foot was placed in the posterior position as compared to the anterior position for preferred and nonpreferred stagger. Knee extension moments were significantly increased at the low seat height as compared to the standard seat height. When shifting the feet anterior or posterior for symmetric placements during sit-to-stand, the most dramatic effect was an increase in hip extension moments when the feet are shifted anteriorly. Utilizing asymmetric foot placements during sit-to-stand produced increases in ankle plantarflexion and knee extension moments for the posteriorly placed limb, with reductions in the anteriorly placed limb.

The effects of postseason break on stabilometric performance in female volleyball players

Ankle sprain is a common injury in volleyball. Poor stabilometric performance (SP) is associated with high risks of sustaining ankle sprain. Balance training can improve SP and reduce ankle sprain, but no research has studied the effects of detraining on SP in highly trained athletes. The purpose of this study was to determine the effects of one-month postseason break on SP in female volleyball players. Eleven NCAA female volleyball players participated in two eye-closed single-leg stance tests before and after a one-month postseason break. Stance time, center of pressure (COP) area, COP standard deviation, and COP mean velocity were assessed during the tests. During the postseason break, subjects conducted self-selected exercise and the average training duration was 87% lower compared to the competition season. Subjects demonstrated significant increases in anterioposterior (A/P) COP standard deviation (1.6 ± 0.4 vs. 1.8 ± 0.4 cm, p = 0.05), mediolateral (M/L) COP velocity (6.5 ± 1.5 vs. 7.1 ± 1.3 cm/s, p = 0.05), and overall COP velocity (10.1 ± 2.0 vs. 11.6 ± 1.9 cm/s, p = 0.02) after postseason break. SP decreased in highly trained female volleyball players after one-month postseason break. The decrease in SP indicated a possible increased risk for ankle sprain injury.

Medial knee joint loading during stair ambulation and walking while carrying loads

Carrying loads while walking or using stairs is a common activity of daily living. Knee osteoarthritis is associated with increased external knee adduction moment (KAM) during walking, so understanding how the additional challenges of stairs and carrying loads impact these moments is of value. Sixteen healthy individuals performed three types of MOTION (walking, stair ascent, stair descent) under three LOAD conditions (no load, carrying a 13.6kg front load, carrying 13.6kg load in a backpack). Three-dimensional gait analysis was used to measure KAM. Results of ANOVA showed a significant main effect of both MOTION and LOAD on peak KAM (p<0.001), but no significant MOTION×LOAD interaction (p=0.250). Peak KAM during stair ascent was about two-times those seen in stair descent (p<0.001) and was significantly higher than those seen in walking (p<0.001). Conditions with LOAD generated significantly greater KAM as compared to the no-LOAD conditions (p<0.001). These findings suggest that carrying a load of moderate magnitude while climbing stairs significantly increases the peak KAM - a risk factor associated with knee osteoarthritis.

The effects of age and type of carrying task on lower extremity kinematics

The purpose of this study was to determine the effects of age, load amount and load symmetry on lower extremity kinematics during carrying tasks. Forty-two participants in four age groups (8–10 years, 12–14 years, 15–17 years and adults) carried loads of 0%, 10% and 20% body weight (BW) in large or small buckets unilaterally and bilaterally. Reflective markers were tracked to determine total joint range of motion and maximum joint angles during the stance phase of walking. Maximum hip extension, hip adduction and hip internal rotation angles were significantly greater for each of the child/adolescent age groups as compared with adults. In addition, maximum hip internal rotation angles significantly increased when carrying a 20% BW load. The observation that the 8–10-year-old age group carried the lightest absolute loads and still displayed the highest maximum hip internal rotation angles suggests a particular necessity in setting carrying guidelines for the youngest children. Statement of Relevance: Bucket-carrying tasks were analysed as a function of age group, load amount and load symmetry. Hip joint rotations significantly increased when carrying 20% BW loads and in children as compared to adults, which suggests a particular necessity in setting carrying guidelines for the youngest age group (8–10 year olds).

Foot placement alters the mechanisms of postural control while standing and reaching

This study investigated the effects of altering foot placement on the strategies used by able-bodied subjects to perform reaching tasks while standing. The motivation for this study was to consider the results in the context of a person with a spinal cord injury using a functional neuromuscular stimulation (FNS) system to stand while reaching. Three foot placement conditions were compared as subjects reached to the left, right, and center. Centers of pressure (COP), joint angles, and joint moments were calculated as postural parameters using force platform and video marker data. Side-by-side and wide foot placements resulted in similar postural parameters. In contrast, the modified tandem stance (feet spaced at pelvic width with one foot shifted forward) resulted in anterior/posterior COP excursions that were larger in magnitude and more consistent across reach directions when compared to the other foot placement conditions. Furthermore, the movement patterns used during the tandem stance were more consistent and may be more readily achievable with FNS than the movement patterns utilized with the side-by-side and wide stances. These results suggest that the modified tandem stance may enhance the functionality of FNS standing systems and may also be useful in other standing rehabilitation programs.