Effect of gait types and external weight carrying strategies on the femoral neck strains during stair descent.

Gait and weight carrying method may change the femoral neck load during stair descent. Applying specific gait and weight carrying methods may reduce the femoral neck load during stair descent, which may reduce hip pain, hip pain related falls and fall related fractures for the older population. The purpose of this study was to test the effect of different gait types (step-over-step v.s. step-by-step) and external weight carrying strategies (ipsilateral v.s. contralateral side) on the femoral neck load, discover which method could reduce the femoral neck load effectively. Seventeen healthy adults from 50 to 70 yrs old were recruited. The kinematic and kinetic analysis, musculoskeletal modelling method were used to estimate the joint and muscle loads for the lower extremities. Finite element analysis was used with the femur model to calculate the femoral neck strains during stair descent with different gait types and weight carrying strategies. The compressive strains were reduced for step-by-step gait method than step-over-step (p<0.015, 12.3-17.4% decrease of strains), the tensile strains were significantly increased for the trailing leg of step-by-step than the leading leg (p<0.001, 24.7% increase of strains). Contralateral weight carrying increased compressive and tensile strains than ipsilateral (p<0.001, 9.9-24.5% increase of strains) in most conditions. Applying step-by-step method and avoiding contralateral side weight carrying could be effective to reduce femoral neck strains. These outcomes could be helpful for the older population to reduce the risks of hip pain, femoral neck pain or pain related falls and fractures.

Dual tasking increases kinematic and kinetic risk factors of ACL injury.

ACL injuries are common among athletes playing team sports. The impact of divided attention during team sports on landing mechanics is unclear. Twenty-one healthy females jumped at a 60° angle to their right and performed a second jump to their right or left at a 60° angle. The direction of the second jump was shown before movement (baseline) or mid-flight of the first jump (dual task). The signal for the dual-task conditions showed five arrows and the middle one indicated the jump direction (Flanker paradigm). The other arrows pointed in the same (congruent) or the opposite (incongruent) direction as the middle arrow. Results indicated larger initial and peak knee flexion angles, smaller peak knee valgus moments, and smaller vertical and posterior GRFs during baseline right jumps compared to other conditions. Peak posterior GRF was increased in the incongruent condition compared to the congruent condition during left jumps. Performance was decreased with longer stance times for the dual task compared to the baseline in both jump directions. Further, the incongruent condition had a longer stance time than the congruent condition during left jumps. More research focusing on decision-making with more challenging visual stimuli mimicking dynamic team sports is merited.

Entry angle during jump landing changes biomechanical risk factors for ACL injury.

ACL injuries are common among athletes. The injury usually occurs during sport movements involving sudden direction changes when landing and cutting. Twenty-one healthy females performed a series of jump-land-jump movements. They jumped from a 28 cm box onto two in-ground force platforms, followed by a maximal vertical jump. The direction of the first jump was tested with seven entry angles, jumping to the right (90 R, 60 R and 30 R), straight forward (0), and jumping to the left (90 L, 60 L and 30 L). Kinematic and kinetic data were recorded for data analysis. During the first 100 ms of landing, participants had significantly smaller peak knee flexion angles, larger initial knee valgus angles and larger peak knee joint external valgus moments when jumping to the right (90 R, 60 R and 30 R) compared to straight forward (0), and jumping to the left (90 L, 60 L and 30 L). Thus, entry angles to the right may increase the risk of ACL injury in the right knee. We suggest that these types of jumps should be used with caution during ACL rehabilitation, but may be useful for testing ACL risk factors in healthy individuals.

Electromyography-based fatigue assessment of an upper body exoskeleton during automotive assembly.

The purpose of this study was to assess an upper body exoskeleton during automotive assembly processes that involve elevated arm postures. Sixteen team members at Toyota Motor Manufacturing Canada were fitted with a Levitate Airframe, and each team member performed between one and three processes with and without the exoskeleton. A total of 16 assembly processes were studied. Electromyography (EMG) data were collected on the anterior deltoid, biceps brachii, upper trapezius, and erector spinae. Team members also completed a usability survey. The exoskeleton significantly reduced anterior deltoid mean active EMG amplitude (p = .01, Δ = -3.2 %MVC, d = 0.56 medium effect) and fatigue risk value (p < .01, Δ = -5.1 %MVC, d = 0.62 medium effect) across the assembly processes, with no significant changes for the other muscles tested. A subset of nine assembly processes with a greater amount of time spent in arm elevations at or above 90° (30 vs. 24%) and at or above 135° (18 vs. 9%) appeared to benefit more from exoskeleton usage. For these processes, the exoskeleton significantly reduced anterior deltoid mean active EMG amplitude (p < .01, Δ = -5.1 %MVC, d = 0.95 large effect) and fatigue risk value (p < .01, Δ = -7.4 %MVC, d = 0.96 large effect). Team members responded positively about comfort and fatigue benefits, although there were concerns about the exoskeleton hindering certain job duties. The results support quantitative testing to match exoskeleton usage with specific job tasks and surveying team members for perceived benefits/drawbacks.

Finite element analysis of femoral neck strains during stair ascent and descent.

For older population, a better understanding of the hip joint loading environment is needed for the prevention of hip pain, and the reduction of the stress fractures and fall risks. Using the motion analysis and inverse dynamics methods, combined with musculoskeletal modelling, static optimization, and finite element (FE) femur model, the difference of femoral neck strains between stair ascent vs. descent, young vs. older populations was compared. A two-way repeated-measures MANOVA was applied to test the effect of age and stair direction on the femoral neck strains. The strains at the femoral neck cross-section were greater for stair descent than ascent for both age groups (mostly P = 0.001 to 0006) but there was no difference between age groups. In this study, femoral neck strains represented bone loading environment in more direct ways than joint reaction forces/moments or joint contact forces, the risk of hip pain, falls and stress fractures might be greater during stair descent than ascent. Possible preventative methods to reduce these risks should be developed in the future studies.

Measuring femoral neck loads in healthy young and older adults during stair ascent and descent.

Understanding the hip loading environment for daily activities is useful for hip fracture prevention, rehabilitation, and the design of osteogenic exercises. Seventeen older adults (50-70 yrs) and twenty young adults (18-30 yrs) were recruited. A rigid body model combined with a musculoskeletal model was used to estimate lower extremity loading. An elliptical cross-section model of the femoral neck was used to estimate femoral neck stress during stair ascent and descent. Two peaks were identified in the stress curves, corresponding to the peaks in the vertical ground reaction force. During stair ascent, significantly higher tension on the superior femoral neck was found for the young group at peak 1 (young: 13.5±6.1 MPa, older: 4.2±6.5 MPa, p<0.001). Also during stair ascent, significantly higher compression on the posterior femoral neck was found for the older group at peak 2 (young: -11.4±4.9 MPa, old: -18.1±8.6 MPa, p = 0.006). No significant difference was found for stair descent. Components of stress (muscle vs. reaction forces; axial forces vs. bending moments) were also examined for each trial of stair ascent and descent. The stresses and their components provided loading magnitude and locations of higher stress on the femoral neck during stair ascent and descent. Understanding femoral neck stresses may be used to help prevent hip fractures, reduce pain, improve rehabilitation, and design osteogenic exercises.

Mediolateral postural stability when carrying asymmetric loads during stair negotiation.

The purpose of this study was to assess postural stability in the medial-lateral (ML) direction when carrying unilateral and bilateral loads during stair negotiation. Twenty-four healthy young adults were instructed to ascend and descend a three step staircase under three load conditions: no load, 20% body mass (BM) bilateral load, and 20% BM unilateral load. A modified time-to-contact (TTC) method was proposed to evaluate postural stability during stair negotiation. Carrying unilateral loads required more rapid postural adjustments as evidenced by lower minimum ML TTC and ML TTC percentage as compared bilateral loads and no load during stair descent. In addition, lower ML TTC and TTC percentage were found for loaded limb stance for stair descent. Taken together, unilateral loads and the loaded leg during stair descent are of concern when considering postural stability during load carriage. These results illustrate differing postural control challenges for stair ascent and descent during load carriage.

Alterations in medial-lateral postural control after anterior cruciate ligament reconstruction during stair use.

BACKGROUND: Dynamic postural control during everyday tasks is poorly understood in people following anterior cruciate ligament reconstruction (ACLR). Understanding dynamic postural control can provide insight into potentially modifiable impairments in people following ACLR who are at increased risk for second ACL injury and/or knee osteoarthritis. RESEARCH QUESTION: Determine whether measures indicative of dynamic postural control differ between individuals with and without ACLR during stair ascent and descent. METHODS: Seventeen individuals with ACLR (>1 yr post-surgery) and 16 age and sex-matched healthy controls participated. Centre of pressure (COP) measures included: i) COP excursion, ii) COP velocity, and iii) dynamic time-toboundary (TTB). Mixed linear models were used to compare COP measures for the ACLR leg, non-ACLR leg, and healthy controls during stair ascent and stair descent. RESULTS: There were no statistically significant differences observed during stair ascent (all p > 0.05). Several statistical differences were found during stair descent for individual with ACLR, but not between those with ACLR and healthy controls. The ACLR leg had higher medial-lateral COP excursion (mean difference 1.06 cm, [95 %CI 0.08-2.06 cm], p = 0.036; effect size = 0.38) compared to the non-ACLR leg during stair descent. In addition, the ACLR leg had a lower medial-lateral TTB (mean difference -13 ms [95 %CI -38 to 2 ms], p = 0.005; effect size = 0.49) and medial-lateral TTB normalized to stance time (mean difference -5.8 % [95 %CI -10.3 to 1.3 %], p = 0.012; effect size = 0.80) compared to the non-ACLR leg during stair descent. No statistical differences were observed for anterior-posterior measures during stair descent (all p > 0.05). SIGNIFICANCE: Taken together, findings indicate that there are small to large differences in medial-lateral postural control in the ACLR leg compared to the non-ACLR leg during stair descent. Further work is required to understand clinical implication of these novel observations.

Acute Effects of Wedge Orthoses and Sex on Iliotibial Band Strain During Overground Running in Nonfatiguing Conditions.

BACKGROUND: Previous research has identified that iliotibial band (ITB) syndrome is more prevalent in females than in males. It has been theorized that high ITB strain rate is a primary etiological factor for developing ITB syndrome. Orthoses are commonly used to influence gait mechanics and may reduce ITB strain rate by influencing alterations in the kinematic chain. OBJECTIVES: To identify how wedge orthoses and sex affect ITB strain and strain rate. METHODS: Thirty asymptomatic participants (15 male, 15 female) ran with 7° lateral, 3° lateral, 0° (no wedge), 3° medial, and 7° medial wedges in this within-subject, repeated-measures study. Participants ran overground while data were collected with a motion-capture system and force platform. Iliotibial band strain and strain rate were estimated using a novel 6-degrees-of-freedom musculoskeletal model. A mixed-model multivariate analysis of covariance for between-subject comparison of sex and within-subject comparison of wedge was used. RESULTS: There were no significant differences in ITB strain or strain rate between wedge conditions. Females had significantly higher ITB strain and strain rate compared to males. CONCLUSION: Clinicians should be aware that medial wedges may not acutely alter ITB strain or strain rate. Females exhibited greater peak ITB strain and strain rate, potentially due to increased hip internal rotation compared to males. Further research is needed to investigate longitudinal effects of the wedges. J Orthop Sports Phys Ther 2019;49(10):743-750. Epub 31 Aug 2019. doi:10.2519/jospt.2019.8837.

Carrying asymmetric loads while walking on an uneven surface.

BACKGROUND: Individuals often carry asymmetric loads over challenging surfaces such as uneven or irregular terrain, which may require a higher demand for postural control than walking on an even surface. RESEARCH QUESTION: The purpose of this study was to assess postural stability in the medial-lateral (ML) direction while carrying unilateral versus bilateral loads when walking on even versus uneven surfaces. METHODS: Nineteen healthy young adults walked on even and uneven surface treadmills under three load conditions: no load, 20% body weight (BW) bilateral load, and 20% BW unilateral load. A Pedar in-shoe pressure system (Novel, Munich, Germany) was used to evaluate center of pressure (COP)-based parameters. RESULTS: Carrying 20% BW bilateral or unilateral loads significantly increased double support ratio. In addition, carrying a 20% BW unilateral load significantly increased coefficient of variation (CV) of double support ratio, CV of ML COP excursion, and CV of ML COP velocity. Walking on an uneven surface significantly increased double support ratio, ML COP excursion, ML COP velocity, and CV of double support ratio. When carrying a 20% BW unilateral load, unloaded limb stance had significantly increased double support ratio and ML COP velocity, although it appears that the loaded limb may be used to make step-by-step adjustments as evidenced by the higher CV of ML COP velocity. SIGNIFICANCE: Unilateral load carriage, walking on uneven surfaces, and unloaded leg stance are of particular concern when considering postural stability.

Carrying asymmetric loads during stair negotiation: Loaded limb stance vs. unloaded limb stance.

BACKGROUND: Individuals often carry items in one hand instead of both hands during activities of daily living. Research Question The purpose of this study was to investigate low back and lower extremity frontal plane moments for loaded limb stance and unloaded limb stance when carrying symmetric and asymmetric loads during stair negotiation. METHODS: Participants were instructed to ascend and descend a three-step staircase at preferred pace using a right leg lead and a left leg lead for each load condition: no load, 20% body weight (BW) bilateral load, and 20% BW unilateral load. L5/S1 contralateral bending, hip abduction, external knee varus, and ankle inversion moments were calculated using inverse dynamics. RESULTS: Peak L5/S1 contralateral bending moments were significantly higher when carrying a 20% BW unilateral load as compared to a 20% BW bilateral load for both stair ascent and stair descent. In addition, peak L5/S1 contralateral bending moments were significantly higher during step one than for step two. Peak external knee varus and hip abduction moments were significantly higher in unloaded limb stance as compared to loaded limb stance when carrying a 20% BW unilateral load. SIGNIFICANCE: General load carriage recommendations include carrying less than 20% BW loads and splitting loads bilaterally when feasible. Assessment recommendations include analyzing the first stair step and analyzing both the loaded and unloaded limbs.

Femoral Neck Stress in Older Adults During Stair Ascent and Descent.

A detailed understanding of the hip loading environment is needed to help prevent hip fractures, minimize hip pain, rehabilitate hip injuries, and design osteogenic exercises for the hip. The purpose of this study was to compare femoral neck stress during stair ascent and descent and to identify the contribution of muscles and reaction forces to the stress environment in mature adult subjects (n = 17; age: 50-65 y). Motion analysis and inverse dynamics were combined with musculoskeletal modeling and optimization, then used as input to an elliptical femoral neck cross-sectional model to estimate femoral neck stress. Peak stress values at the 2 peaks of the bimodal stress curves (stress vs time plot) were compared between stair ascent and descent. Stair ascent had greater compressive stress than descent during the first peak at the anterior (ascent: -18.0 [7.9] MPa, descent: -12.9 [5.4] MPa, P < .001) and posterior (ascent: -34.4 [10.9] MPa, descent: -27.8 [10.1] MPa, P < .001) aspects of the femoral neck cross section. Stair descent had greater tensile stress during both peaks at the superior aspect (ascent: 1.3 [7.0] MPa, descent: 24.8 [9.7] MPa, peak 1: P < .001; ascent: 15.7 [6.1] MPa, descent: 18.0 [8.4] MPa, peak 2: P = .03) and greater compressive stress during the second peak at the inferior aspect (ascent: -43.8 [9.7] MPa, descent: -51.1 [14.3] MPa, P = .004). Understanding this information can provide a more comprehensive view of bone loading at the femoral neck for older population.

Kinematic and Kinetic Indicators of Sit-to-Stand.

Variation in the timing indicators separating sit-to-stand (STS) into movement phases complicates both research comparisons and clinical applications. The purpose of this study was to use kinetic reference standards to identify accurate kinematic and kinetic indicators for STS movement analysis such that consistent indicators might be used for STS from varied initial postures. Healthy adults performed STS using 4 foot placements: foot-neutral, foot-back, right-staggered, and left-staggered. Kinetic and kinematic data were collected from force platforms and an 8-camera video system. Initiation, seat-off, vertical posture, and termination were detected with 5% start and 7.5% end thresholds for changes in kinetic and kinematic STS indicators. Timing differences between kinetic and kinematic indicator time points and the reference vertical seated reaction force end point (seat-off) were determined. Kinematic indicators were compared with selected kinetic indicators using timing differences, statistical similarity, and internal consistency measures. Our results suggest that a single force platform system measuring vertical GRF or a simple camera system to evaluate the shoulder marker position and velocity can accurately and consistently detect STS initiation, seat-off, and vertical posture. In addition, these suggested STS indicators for initiation, seat-off, and vertical posture were not dependent upon foot placement.

Muscle activity amplitudes and co-contraction during stair ambulation following anterior cruciate ligament reconstruction.

The purpose of this study was to compare muscle activity amplitudes and co-contraction in those with anterior cruciate ligament (ACL) reconstruction to healthy controls during stair negotiation. Eighteen participants with unilateral ACL reconstruction and 17 healthy controls performed stair ascent and descent while surface electromyography was recorded from knee and hip musculature. During stair ascent, the ACL group displayed higher gluteus maximus activity (1-50% stance, p = 0.02), higher vastus lateralis:biceps femoris co-contraction (51-100% stance, p = 0.01), and higher vastus lateralis:vastus medialis co-contraction (51-100% stance, p = 0.05). During stair descent, the ACL group demonstrated higher gluteus maximus activity (1-50% stance, p = 0.01; 51-100% stance, p < 0.01), lower rectus femoris activity (1-50% stance, p = 0.04), higher semimembranosus activity (1-50% stance, p=0.01), higher gluteus medius activity (51-100% stance, p = 0.01), and higher vastus medialis:semimembranosus co-contraction (1-50% stance, p = 0.02). While the altered muscle activity strategies observed in the ACL group may act to increase joint stability, these strategies may alter joint loading and contribute to post-traumatic knee osteoarthritis often observed in this population. Our results warrant further investigation to determine the longterm effects of altered muscle activity on the knee joint following ACL reconstruction.

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 postseason break on knee biomechanics and lower extremity EMG in a stop-jump task: implications for ACL injury.

The effects of training on biomechanical risk factors for anterior cruciate ligament (ACL) injuries have been investigated, but the effects of detraining have received little attention. The purpose of this study was to evaluate the effects of a one-month postseason break on knee biomechanics and lower extremity electromyography (EMG) during a stop-jump task. A postseason break is the phase between two seasons when no regular training routines are performed. Twelve NCAA female volleyball players participated in two stop-jump tests before and after the postseason break. Knee kinematics, kinetics, quadriceps EMG, and hamstring EMG were assessed. After one month of postseason break, the players demonstrated significantly decreased jump height, decreased initial knee flexion angle, decreased knee flexion angle at peak anterior tibial resultant force, decreased prelanding vastus lateralis EMG, and decreased prelanding biceps femoris EMG as compared with prebreak. No significant differences were observed for frontal plane biomechanics and quadriceps and hamstring landing EMG between prebreak and postbreak. Although it is still unknown whether internal ACL loading changes after a postseason break, the more extended knee movement pattern may present an increased risk factor for ACL injuries.

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.

Lower extremity joint moments during carrying tasks in children.

Farm youth often carry loads that are proportionally large and/or heavy, and field measurements have determined that these tasks are equivalent to industrial jobs with high injury risks. The purpose of this study was to determine the effects of age, load amount, and load symmetry on lower extremity joint moments during carrying tasks. Three age groups (8-10 years, 12-14 years, adults), three load amounts (0%, 10%, 20% BW), and three load symmetry levels (unilateral large bucket, unilateral small bucket, bilateral small buckets) were tested. Inverse dynamics was used to determine maximum ankle, knee, and hip joint moments. Ankle dorsiflexion, ankle inversion, ankle eversion, knee adduction, and hip extension moments were significantly higher in 8-10 and 12-14 year olds. Ankle plantar flexion, ankle inversion, knee extension, and hip extension moments were significantly increased at 10% and 20% BW loads. Knee and hip adduction moments were significantly increased at 10% and 20% BW loads when carrying a unilateral large bucket. Of particular concern are increased ankle inversion and eversion moments for children, along with increased knee and hip adduction moments for heavy, asymmetrical carrying tasks. Carrying loads bilaterally instead of unilaterally avoided increases in knee and hip adduction moments with increased load amount.

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.