Effects of Body Weight Support in Running on Achilles Tendon Loading.

Achilles tendon (AT) tendinopathy is common in runners. Repetitive AT loading may play a role in etiology. Interventions such as body weight support (BWS) may reduce loading on the AT in running. Examine how ground reaction force, AT loading, foot strike, and cadence variables change in running with BWS. Twenty-four healthy female runners free from injury were examined. Participants ran on an instrumented treadmill with and without BWS using a harness-based system at a standardized speed. The system has 4 elastic cords affixed to a harness that is attached to a frame-like structure. Kinematic data and kinetic data were used in a musculoskeletal model (18 segments and 16 degrees of freedom) to determine AT loading variables, foot strike angle, and cadence. Paired t-tests were used to compare each variable between conditions. Ground reaction force was 9.0% lower with BWS (p<.05). Peak AT stress, force, and impulse were 9.4, 11.7%, and 14.8% lower when using BWS in running compared to no support (p<.05). Foot strike angle was similar (p<.05) despite cadence being reduced (p<.05). BWS may reduce AT loading and impulse variables during running. This may be important in rehabilitation efforts.

Alterations in Achilles tendon stress and strain across a range of running velocities.

Running has a high incidence of overuse injuries. Achilles tendon (AT) injuries may occur due to high forces and repetitive loading during running. Foot strike pattern and cadence have been linked to the magnitude of AT loading. The effect of running speed on AT stress and strain, muscle forces, gait parameters and running kinematics is not well addressed in recreational runners with lower pace of running. Twenty-two female participants ran on an instrumented treadmill between 2.0 and 5.0 m/s. Kinetic and kinematic data were obtained. AT cross-sectional area data were collected using ultrasound imaging. Inverse dynamics with static optimization was used to calculate muscle forces and AT loading. AT stress, strain and cadence increased with greater running speed. Foot inclination angle indicated a rearfoot strike pattern among all participants, which increased as running speed increased but the latter plateaued after 4.0 m/s. The soleus contributed more force in running compared to the gastrocnemius throughout all speeds. Highest running speeds had the most stress on the AT, with changes to foot inclination angle and cadence. Understanding the relation of AT loading variables with running speed may aid in understanding how applied load may influence injury.

Effect of Hamstring-to-quadriceps Ratio on Knee Forces in Females During Landing.

ACL injuries in the athletic population are a common occurrence with over 70% associated with non-contact mechanisms. The hamstring to quadriceps ratio is a widely used clinical measure to assess an athlete's readiness to return to sport; however, its relationship to knee forces and ACL tension during landing is unknown. Baseline isokinetic testing was completed on 100 college-aged females. Subjects with strength ratios 0.4 (n=20) and those with ratios of 0.6 (n=20) returned for an assessment of their drop landing. A sagittal plane knee model determined the low ratio group demonstrated 16.6% larger ligament shear (p=0.000), a 26% increase in tibiofemoral shear force (p=0.026) and a 6% increase vertical force between the femur and tibial plateau (p=0.026) compared to the high hamstring ratio group within 100 ms upon impact. The lower ratio group also demonstrated 9.5% greater maximal quadriceps (p=0.028) force during landing. These findings suggest that the hamstring to quadriceps ratio may be related to knee forces and ACL loading during landing. This metric may augment clinical decision making regarding an athlete's readiness to return to sport or relative risk for re-injury.

Patellofemoral Joint Stress during Running with Added Load in Females.

Patellofemoral joint (PFJ) pain syndrome is a commonly reported form of pain in female runners and military personnel. Increased PFJ stress may be a contributing factor. Few studies have examined PFJ stress running with added load. Our purpose was to analyze PFJ stress, PFJ reaction force, quadriceps force, knee flexion angle, and other kinematic and temporospatial variables running with and without a 9 kg load. Nineteen females ran across a force platform with no added load and 9.0 kg weight vest. Kinematic data were collected using 3D motion capture and kinetic data with a force platform. Muscle forces were estimated using a musculoskeletal model, and peak PFJ loading variables were calculated during stance. Multivariate analyses were run on PFJ loading variables and on cadence, step length and foot strike index. Differences were shown in PFJ stress, PFJ reaction force, peak knee flexion angle and quadriceps force. Joint specific kinetic variables increased between 5-16% with added load. PFJ loading variables increased with 9 kg of added load without changes in cadence, step length, or foot strike index compared to no load. Added load appears to increase the PFJ loading variables associated with PFJ pain in running.

Muscle force characteristics of male and female collegiate cross-country runners during overground running.

Males and females demonstrate unique running mechanics that may contribute to sex-related differences in common running related injuries. Understanding differences in muscle forces during running may inform intervention approaches, such as gait retraining addressing muscle force distribution. The purpose of this study was to compare muscle force characteristics and inter-trial variability between males and females during running. Twenty female and 14 male collegiate cross-country runners were examined. Three-dimensional kinetic and kinematic data were collected during overground running and used to estimate muscle forces via musculoskeletal modelling. Principle components analysis was used to capture the primary sources of variance from the muscle force waveforms. The magnitude of the forces for the hamstrings, gastrocnemius, and soleus muscles were higher across the majority of stance in male runners regardless of footstrike pattern. Males also demonstrated greater inter-trial variability in the timing of the peak gluteus maximus force and the magnitude of local peaks in the gastrocnemius force waveform. Male and female collegiate cross-country runners appear to employ unique lower extremity muscle force characteristics during overground running.

Patellofemoral Joint Loading During Single-Leg Hopping Exercises.

CONTEXT: Single-leg hopping is used to assess a dynamic knee stability. Patellofemoral pain is often experienced during these exercises, and different cadences of jumping are often used in rehabilitation for those with patellofemoral pain. No studies to date have examined patellofemoral joint loading during single-leg hopping exercise with different hopping cadences. OBJECTIVE: To determine if single-leg hopping at 2 different cadences (50 and 100 hops per minute [HPM]) leads to a significant difference in patellofemoral joint loading variables. SETTING: University research laboratory. PARTICIPANTS: Twenty-five healthy college-aged females (age 22.3 [1.8] y, height 171.4 [6.3] cm, weight 67.4 [9.5] kg, Tegner Activity Scale 4.75 [1.75]) participated. MAIN OUTCOME MEASURES: Three-dimensional kinematic and kinetic data were measured using a 15-camera motion capture system and force platform. Static optimization was used to calculate muscle forces and then used in a musculoskeletal model to determine patellofemoral joint stress (PFJS), patellofemoral joint reaction force (PFJRF), quadriceps force (QF), and PFJRF loading rate, during the first and last 50% of stance phase. RESULTS: Greater maximal PFJRF occurred at 100 HPM, whereas greater PFJRF loading rate occurred at 50 HPM. However, overall peak QF and peak PFJS were not different between the 2 cadences. At 50 HPM, there was greater PFJS, PFJRF, peak PFJRF loading rate, and peak QF during the first 50% of stance when compared with the last 50%. CONCLUSION: Training at 50 HPM may reduce PFJRF and PFJRF loading rate, but not PFJS or QF. Patellofemoral joint loading variables had significantly higher values during the first half of the stance phase at the 50 HPM cadence. This may be important with training individuals with patellofemoral pain.

Effects of Relative Drop Heights of Drop Jump Biomechanics in Male Volleyball Players.

Previous cross-sectional studies have reported that higher drop heights do not always result in improved performance, and may increase injury risk during drop jumps (DJ). The purpose of this study was to analyze the kinematics and kinetics during the DJ in order to determine the relative drop height that maximize performance without exposing the lower extremity joints to unnecessary loads. Twenty male Division I college volleyball players volunteered. Data were collected using 11 infrared cameras and two force platforms. Participants performed three maximal effort countermovement jumps (CMJ). Subsequently, 50, 75, 100, 125, and 150% CMJ height (CMJH) was used to scale their relative drop height for three DJ trials per height. There was a significant increase in the landing phase impulse when the drop height exceeded 100%CMJH (p<0.05). At 125% and 150%CMJH, the negative work of knee and ankle significantly increased. The incoming velocity, kinetic energy, landing depth, maximum ground reaction force, landing impulse and power absorption of knee and ankle all increased with drop height (p<0.05). DJ height and reactive strength index following the drop landing were not statistically different between any of the drop heights (p>0.05). 50% to 100%CMJH may be the appropriate individual relative drop height for the DJ.

Effects of Anterior Knee Displacement During Squatting on Patellofemoral Joint Stress.

CONTEXT: Squatting is a common rehabilitation training exercise for patellofemoral pain syndrome (PFPS). Patellofemoral joint stress (PFJS) during squatting with more anterior knee displacement has not been systematically investigated. OBJECTIVE: To compare PFJS during squatting using 2 techniques: squat while keeping the knees behind the toes (SBT) and squat while allowing the knees to go past the toes (SPT). SETTING: University research laboratory. PARTICIPANTS: Twenty-five healthy females (age: 22.69 (0.74) y; height: 169.39 (6.44) cm; mass: 61.55 (9.74) kg) participated. MAIN OUTCOME MEASURES: Three-dimensional kinematic and kinetic data were collected at 180 and 1800 Hz, respectively. A musculoskeletal model was used to calculate muscle forces through static optimization. These muscle forces were used in a patellofemoral joint model to estimate PFJS. RESULTS: The magnitudes of PFJS, reaction force, and quadriceps force were higher (P < .001) during SPT compared with the SBT technique. Knee flexion, hip flexion, and ankle dorsiflexion angles were reduced when using the SBT technique. CONCLUSIONS: Findings provide some general support for minimizing forward knee translation during squats for patients that may have patellofemoral pain syndrome.

Optimum Drop Jump Height in Division III Athletes: Under 75% of Vertical Jump Height.

Our purpose was to evaluate the vertical ground reaction force, impulse, moments and powers of hip, knee and ankle joints, contact time, and jump height when performing a drop jump from different drop heights based on the percentage of a performer's maximum vertical jump height (MVJH). Fifteen male Division III athletes participated voluntarily. Eleven synchronized cameras and two force platforms were used to collect data. One-way repeated-measures analysis of variance tests were used to examine the differences between drop heights. The maximum hip, knee and ankle power absorption during 125%MVJH and 150%MVJH were greater than those during 75%MVJH. The impulse during landing at 100%MVJH, 125%MVJH and 150%MVJH were greater than 75%MVJH. The vertical ground reaction force during 150%MVJH was greater than 50%MVJH, 75%MVJH and 100%MVJH. Drop height below 75%MVJH had the most merits for increasing joint power output while having a lower impact force, impulse and joint power absorption. Drop height of 150%MVJH may not be desirable as a high-intensity stimulus due to the much greater impact force, increasing the risk of injury, without increasing jump height performance.

Effects of Foot Strike and Step Frequency on Achilles Tendon Stress During Running.

Achilles tendon (AT) injuries are common in runners. The AT withstands high magnitudes of stress during running which may contribute to injury. Our purpose was to examine the effects of foot strike pattern and step frequency on AT stress and strain during running utilizing muscle forces based on a musculoskeletal model and subject-specific ultrasound-derived AT cross-sectional area. Nineteen female runners performed running trials under 6 conditions, including rearfoot strike and forefoot strike patterns at their preferred cadence, +5%, and -5% preferred cadence. Rearfoot strike patterns had less peak AT stress (P < .001), strain (P < .001), and strain rate (P < .001) compared with the forefoot strike pattern. A reduction in peak AT stress and strain were exhibited with a +5% preferred step frequency relative to the preferred condition using a rearfoot (P < .001) and forefoot (P=.005) strike pattern. Strain rate was not different (P > .05) between step frequencies within each foot strike condition. Our results suggest that a rearfoot pattern may reduce AT stress, strain, and strain rate. Increases in step frequency of 5% above preferred frequency, regardless of foot strike pattern, may also lower peak AT stress and strain.

Differences in joint-position sense and vibratory threshold in runners with and without a history of overuse injury.

CONTEXT: A relationship between altered postural control and injury has been reported in sports. Sensorimotor function serves a fundamental role in postural control and is not often studied in runners. Persons who sustain running injury may have altered sensorimotor function contributing to risk of injury or reinjury. OBJECTIVES: To determine if differences in knee and ankle proprioception or plantar sensation exist between injured and noninjured runners. DESIGN: Retrospective case-control study. SETTING: University campus. PARTICIPANTS: Twenty runners with a history of lower-extremity overuse injury and 20 noninjured runners were examined. Injured runners were subcategorized into 2 groups based on site of injury: foot/ankle and knee/hip. MAIN OUTCOME MEASURES: Active absolute joint-repositioning error of the ankle at 20° inversion and 10° eversion and the knee at 15° and 40° flexion was assessed using an isokinetic dynamometer. Vibratory threshold at the calcaneus, arch, and great toe was determined for each subject using a handheld electric sensory threshold instrument. RESULTS: Runners in the injured-foot/ankle group had increased absolute error during ankle-eversion repositioning (6.55° ± 3.58°) compared with those in the noninjured (4.04° ± 1.78°, P = .01) and the hip/knee (3.63° ± 2.2°, P = .01) groups. Runners in the injured group, as a whole, had greater sensitivity in the arch of the plantar surface (2.94 ± 0.52 V) than noninjured runners (2.38 ± 0.53 V, P = .02). CONCLUSIONS: Differences in ankle-eversion proprioception between runners with a history of ankle and foot injuries and noninjured runners were observed. Runners with a history of injury also displayed an increased vibratory threshold in the arch region compared with noninjured runners. Poor ankle-joint-position sense and increased plantar sensitivity suggest altered sensorimotor function after injury. These factors may influence underlying postural control and contribute to altered loading responses commonly observed in injured runners.

Two- and Three-Dimensional Relationships Between Knee and Hip Kinematic Motion Analysis: Single-Leg Drop-Jump Landings.

CONTEXT: Hip- and knee-joint kinematics during drop landings are relevant to lower-extremity injury mechanisms. In clinical research the "gold standard" for joint kinematic assessment is 3-dimensional (3D) motion analysis. However, 2-dimensional (2D) kinematic analysis is an objective and feasible alternative. OBJECTIVE: To quantify the relationship between 2D and 3D hip and knee kinematics in single-leg drop landings and test for a set of 3D hip and knee kinematics that best predicts 2D kinematic measures during single-leg drop landings Design: Descriptive, comparative laboratory study. PARTICIPANTS: 31 healthy college-age women (65.5 kg [SD 12.3], 168.1 cm [SD 6.7]). METHODS: Participants performed five 40-cm single-leg landings during motion capture at 240 Hz. Multiple regressions were used to predict relationships for knee and hip between 2D frontal-plane projection angles (FPPA) and 3D measurements. RESULTS: 2D knee FPPA had a strong relationship with 3D frontal-plane knee kinematics at initial contact (IC) (r2 = .72), which was only minimally improved with the addition of knee sagittal-plane and hip transverse-plane positions at IC (r2 = .77). In contrast, 2D knee FPPA had a low relationship with 3D knee-abduction excursion (r2 = .06). The addition of knee sagittal-plane and hip transverse-plane motions did not improve this relationship (r2 = .14). 2D hip FPPA had a moderate relationship with 3D frontal-plane hip position at IC (r2 = .52), which was strengthened with the addition of hip sagittal-plane position (r2 = .60). In addition, hip 2D FPPA into adduction excursion had a strong association with 3D hip-adduction excursion (r2 = .70). CONCLUSION: 2D kinematics can predict 3D frontal-plane hip and knee position at IC during a single-leg landing but predict 3D frontal-plane knee excursion with far less accuracy.

Kinetic comparison of the power development between power clean variations.

The purpose of this study was to compare the power production of the hang clean (HC), jump shrug (JS), and high pull (HP) when performed at different relative loads. Seventeen men with previous HC training experience, performed 3 repetitions each of the HC, JS, and HP at relative loads of 30, 45, 65, and 80% of their 1 repetition maximum (1RM) HC on a force platform over 3 different testing sessions. Peak power output (PPO), peak force (PF), and peak velocity (PV) of the lifter plus bar system during each repetition were compared. The JS produced a greater PPO, PF, and PV than both the HC (p < 0.001) and HP (p < 0.001). The HP also produced a greater PPO (p < 0.01) and PV (p < 0.001) than the HC. Peak power output, PF, and PV occurred at 45, 65, and 30% 1RM, respectively. Peak power output at 45% 1RM was greater than PPO at 65% (p = 0.043) and 80% 1RM (p = 0.004). Peak force at 30% was less than PF at 45% (p = 0.006), 65% (p < 0.001), and 80% 1RM (p = 0.003). Peak velocity at 30 and 45% was greater than PV at 65% (p < 0.001) and 80% 1RM (p < 0.001). Peak velocity at 65% 1RM was also greater than PV at 80% 1RM (p < 0.001). When designing resistance training programs, practitioners should consider implementing the JS and HP. To optimize PPO, loads of approximately 30 and 45% 1RM HC are recommended for the JS and HP, respectively.

Effects of medially wedged foot orthoses on knee and hip joint running mechanics in females with and without patellofemoral pain syndrome.

We examined the effects of medially wedged foot orthoses on knee and hip joint mechanics during running in females with and without patellofemoral pain syndrome (PFPS). We also tested if these effects depend on standing calcaneal eversion angle. Twenty female runners with and without PFPS participated. Knee and hip joint transverse and frontal plane peak angle, excursion, and peak internal knee and hip abduction moment were calculated while running with and without a 6° full-length medially wedged foot orthoses. Separate 3-factor mixed ANOVAs (group [PFPS, control] x condition [medial wedge, no medial wedge] x standing calcaneal angle [everted, neutral, inverted]) were used to test the effect of medially wedged orthoses on each dependent variable. Knee abduction moment increased 3% (P = .03) and hip adduction excursion decreased 0.6° (P < .01) using medially wedged foot orthoses. No significant group x condition or calcaneal angle x condition effects were observed. The addition of medially wedged foot orthoses to standardized running shoes had minimal effect on knee and hip joint mechanics during running thought to be associated with the etiology or exacerbation of PFPS symptoms. These effects did not appear to depend on injury status or standing calcaneal posture.

Kinematic and muscle force asymmetry in healthy runners: How do different methods measure up?

BACKGROUND: Comparing the performance of one leg to another is a common means of assessing running gait to help inform clinical management strategies. Various methods are employed to quantify asymmetries between limbs. However, limited data is available describing the amount of asymmetry that may be expected during running and no index has been identified as preferable for making a clinical determination of asymmetry. Therefore, this study aimed to describe amounts of asymmetry in collegiate cross-country runners and compare different methods of calculating asymmetry. RESEARCH QUESTION: What can be expected as a normal amount of asymmetry in biomechanical variables in healthy runners when using different indices to quantify limb symmetry? METHODS: Sixty-three (29 male and 34 female) runners participated. Running mechanics were assessed during overground running using 3D motion capture and a musculoskeletal model using static optimization to estimate muscle forces. Independent t-tests were utilized to determine statistical differences in variables between legs. Different methods of quantifying asymmetry were then compared to statistical differences between limbs to determine cut-off values and the sensitivity and specificity of each method. RESULTS: A large portion of runners demonstrated asymmetry during running. Kinematic variables can be expected to have small differences (2-3 degrees) between limbs while muscle forces may show greater amounts of asymmetry. The sensitivities and specificities for each method of calculating asymmetry were similar, however, different methods led to different cut-off values for each variable investigated. SIGNIFICANCE: Asymmetry can be expected between limbs during running. However, when assessing asymmetry, practitioners should consider the joint, variable, and method of calculating asymmetry when determining differences between limbs.

Dynamic postural control in injured collegiate cross-country runners is not associated with running-related injury.

BACKGROUND: Biomechanical factors have been associated with running-related injury, but associations are unclear. Dynamic postural stability may be a factor related to injury that has not been studied extensively. RESEARCH QUESTION: Does dynamic postural control differ in those with a history of running-related injury or those who go on to sustain a running-related injury? METHODS: Sixty-five (45 injured; 20 uninjured) and fifty-eight (13 injured; 45 uninjured) collegiate cross-country runners were available for our retrospective and prospective analyses. Time to stabilization and dynamic postural stability index were collected during two separate jump landing tasks (forward and lateral direction) for each leg. Retrospective injury was tabulated by a running history survey. Prospective injuries were recorded by a licensed athletic trainer during the competitive season. Differences in postural stability were compared between injured and uninjured groups and between limbs using two-way ANOVA's. An overall group by leg comparison was completed for each task. RESULTS: The non-dominant limb demonstrated better postural stability indices regardless of injury history. An interaction was observed between limbs and history of injury for the anterior-posterior time to stabilization for the lateral task. The non-dominant limb demonstrated better medio-lateral postural stability indices and time to stabilization during the lateral task, regardless of prospective injury. SIGNIFICANCE: Dynamic postural stability was reduced in the dominant limb, but no clear differences were seen between injured and uninjured runners. This suggests dynamic postural stability may be altered in individuals with a history of a running-related injury, but no relationship to subsequent injury was substantiated. Further work is needed to understand how dynamic postural stability may be related to running-related injury.

Concurrent Force Feedback on Load Symmetry in Total Knee Arthroplasty Patients.

Background and Purpose: Load asymmetry can be present before and after total knee arthroplasty (TKA), which may affect progress during knee rehabilitation in an outpatient sports medicine setting. Current rehabilitation primarily focuses on strength, pain, and range of motion deficits; however, recent evidence suggests the use of movement retraining strategies such as load feedback to address load asymmetry. Therefore, the purpose of this study was to examine how a single session of concurrent force feedback influences load symmetry during the leg-press and body-weight squat exercises in individuals following TKA. Additionally, a secondary purpose was to examine the retention of any changes over the course of a week. Study design: Case-series study. Methods: This observational, repeated-measures study design examined the effect of concurrent force feedback training on the mean and standard deviation of load symmetry index during the leg press and squat exercises in 26 patients with TKA in an outpatient sports medicine clinic.The load asymmetry was measured with loadpad sensors placed underneath the each extremity during leg press and squat (baseline), after one training session consisting of concurrent force feedback during these exercises within a single physical therapy session (post feedback), and after seven to ten days of a washout period (post retention). Separate 2 x 3 repeated measures analysis of variance was used to compare the mean and standard deviation of load symmetry across exercise (leg press and squat) and across time (baseline, post feedback and post retention). Results: There was a time effect for the mean load symmetry index (p=0.027) but not for the standard deviation (p=0.441) during these exercises. The leg press showed a greater mean symmetry index compared to the squat regardless of time (p=0.001). Conclusions: A reduction in the mean load symmetry index following concurrent feedback training suggests improved use of the surgical limb during both leg press and squat exercises during the same therapy session but the more symmetric loading pattern was not retained one week later. Overall, the leg press showed greater mean asymmetry than the squat. Standard deviation in the load symmetry index did not change across time or by exercise. Level of Evidence: 3©The Author(s).

Added mass increases Achilles tendon stress in female runners.

CONTEXT: Achilles tendon (AT) injuries are common in female runners and military personnel where increased AT loading may be a contributing factor. Few studies have examined AT stress during running with added mass. The purpose was to examine the stress, strain, and force placed on the AT, kinematics and temporospatial variable in running with different amounts of added mass. DESIGN: Repeated measure design METHODS: Twenty-three female runners with a rear-foot strike pattern were participants. AT stress, strain, and force were measured during running using a musculoskeletal model that used kinematic (180 Hz) and kinetic data (1800 Hz) as input. Ultrasound data were used to measure AT cross sectional area. A repeated measures multivariate analysis of variance (α = 0.05) was used on AT loading variables, kinematics and temporospatial variables. RESULTS: Peak AT stress, strain, and force were greatest during the 9.0 kg added load running condition (p < .0001). There was a 4.3% and 8.8% increase in AT stress and strain during the 4.5 kg and 9.0 kg added load conditions, respectively, compared to baseline. Kinematics at the hip and knee changed with added load but not at the ankle. Small changes in temporospatial variables were seen. CONCLUSION: Added load increased stress on the AT during running. There may be an increased risk for AT injury with added load. Individuals may consider slowly progressing training with added load to allow for increased AT loading.

A comparison of two isometric tests of trunk flexor endurance.

This study was performed to determine the test-retest reliability and the relationship between 2 tests of trunk flexor muscular endurance-a prone bridge and a modified V-sit. Hold times (in seconds) were measured on 60 healthy volunteers from a University community (17 men, 43 women). Both tests were performed at 1-week intervals. The test-retest reliability of each test was assessed with a subgroup of 10 participants during 3 additional testing sessions at 1-week intervals. One examiner collected all data. Intraclass correlation coefficients (2, 1) with the prone bridge were 0.95 and 0.71 with the modified V-sit. The mean hold time was 92.8 ± 44.4 seconds during the prone bridge and 141.7 ± 104.1 seconds during the modified V-sit. Pearson's correlation coefficients between the 2 tests ranged from r = 0.52 (men + women) to r = 0.87 (men only). Intersession reliability with a single examiner was higher with the prone bridge compared with that in the modified V-sit. Modifications to the V-sit resulted in a lower test-retest reliability than was previously reported. Correlations between prone bridge and modified V-sit test scores were low, which may be attributable to the differences in the level of trunk flexor muscle activation between the tests.

Predicting lower body power from vertical jump prediction equations for loaded jump squats at different intensities in men and women.

The purpose of this study was to determine the efficacy of estimating peak lower body power from a maximal jump squat using 3 different vertical jump prediction equations. Sixty physically active college students (30 men, 30 women) performed jump squats with a weighted bar's applied load of 20, 40, and 60% of body mass across the shoulders. Each jump squat was simultaneously monitored using a force plate and a contact mat. Peak power (PP) was calculated using vertical ground reaction force from the force plate data. Commonly used equations requiring body mass and vertical jump height to estimate PP were applied such that the system mass (mass of body + applied load) was substituted for body mass. Jump height was determined from flight time as measured with a contact mat during a maximal jump squat. Estimations of PP (PP(est)) for each load and for each prediction equation were compared with criterion PP values from a force plate (PP(FP)). The PP(est) values had high test-retest reliability and were strongly correlated to PP(FP) in both men and women at all relative loads. However, only the Harman equation accurately predicted PP(FP) at all relative loads. It can therefore be concluded that the Harman equation may be used to estimate PP of a loaded jump squat knowing the system mass and peak jump height when more precise (and expensive) measurement equipment is unavailable. Further, high reliability and correlation with criterion values suggest that serial assessment of power production across training periods could be used for relative assessment of change by either of the prediction equations used in this study.