Whipping or tearing? The biomechanics of Achilles tendinopathy in rearfoot strike runners.

BACKGROUND: Two biomechanical mechanisms for the development of Achilles tendinopathy in runners have been proposed: A whipping mechanism characterized by prolonged and excessive rearfoot eversion, and a tearing mechanism characterized by high eccentric plantar flexor forces. The purpose of this pilot study was to determine if runners with and without a history of Achilles tendinopathy exhibited gait biomechanics consistent with either of these mechanisms. METHODS: Seven male runners with previous or current Achilles tendinopathy and seven healthy male control runners were evaluated by three-dimensional gait analysis. Peak rearfoot eversion angle, rearfoot eversion excursion, duration of rearfoot eversion, and peak rearfoot inversion angle were compared between groups to evaluate the whipping mechanism of injury. Peak dorsiflexion angle, peak dorsiflexion velocity, and peak ankle power absorption were compared between groups to evaluate the tearing mechanism. Additionally, rearfoot eversion angle and sagittal plane ankle power waveforms were compared between groups using statistical parametric mapping. FINDINGS: There were no differences in any rearfoot eversion, inversion, or dorsiflexion variables or waveforms during running in the Achilles tendinopathy group compared to controls. INTERPRETATION: Rearfoot strike runners with Achilles tendinopathy do not exhibit running biomechanics consistent with either the whipping or tearing mechanisms of injury.

Minimum Sampling Frequency for Accurate and Reliable Tibial Acceleration Measurements During Rearfoot Strike Running in the Field.

Field-based tibial acceleration measurements are increasingly common but sampling frequencies vary between accelerometers. The purpose of this study was to determine the minimum sampling frequency needed for reliable and accurate measurement of peak axial and resultant tibial acceleration during running in the field. Tibial acceleration was measured at 7161 Hz in 19 healthy runners on concrete and grass. Acceleration data were down sampled to approximate previously used sampling frequencies. Peak axial and resultant tibial acceleration were calculated for each sampling frequency. The within-session reliability and accuracy of peak axial and resultant tibial accelerations were evaluated using intraclass correlation coefficients, mean differences, and 95% limits of agreements. Intraclass correlation coefficients greater than .9 indicated excellent within-session reliability for both peak axial and resultant tibial acceleration measured while running on concrete and grass. Peak axial and resultant tibial accelerations were 0.5 to 1.4 g lower and minimal detectable differences were up to 0.6 g higher at 102 Hz compared with higher sampling frequencies. We recommend a minimum sampling frequency of 199 Hz for accurate and reliable measurements of peak axial and resultant tibial acceleration in the field.

Biomechanics associated with tibial stress fracture in runners: A systematic review and meta-analysis.

BACKGROUND: Tibial stress fracture (TSF) is an overuse running injury with a long recovery period. While many running studies refer to biomechanical risk factors for TSF, only a few have compared biomechanics in runners with TSF to controls. The aim of this systematic review and meta-analysis was to evaluate biomechanics in runners with TSF compared to controls. METHODS: Electronic databases PubMed, Web of Science, SPORTDiscus, Scopus, Cochrane, and CINAHL were searched. Risk of bias was assessed and meta-analysis conducted for variables reported in 3 or more studies. RESULTS: The search retrieved 359 unique records, but only the 14 that compared runners with TSF to controls were included in the review. Most studies were retrospective, 2 were prospective, and most had a small sample size (5-30 per group). Many variables were not significantly different between groups. Meta-analysis of peak impact, active, and braking ground reaction forces found no significant differences between groups. Individual studies found larger tibial peak anterior tensile stress, peak posterior compressive stress, peak axial acceleration, peak rearfoot eversion, and hip adduction in the TSF group. CONCLUSION: Meta-analysis indicated that discrete ground reaction force variables were not statistically significantly different in runners with TSF compared to controls. In individual included studies, many biomechanical variables were not statistically significantly different between groups. However, many were reported by only a single study, and sample sizes were small. We encourage additional studies with larger sample sizes of runners with TSF and controls and adequate statistical power to confirm or refute these findings.

Changes in Walking Biomechanics after a 30-Min Exercise Bout in Sedentary Compared with Active Young Women.

INTRODUCTION: Patellofemoral pain (PFP) is a common overuse injury associated with physical activity, including walking. The risk for PFP may increase if walking biomechanics change during a bout of walking. Because walking for exercise is often recommended to previously sedentary adults, this would be a cause for concern. The purpose of this study was to determine any differences in walking biomechanics associated with PFP between sedentary and active young women initially and after 30 min of walking for exercise. METHODS: Fifteen sedentary and 15 active young women walked overground for five trials of three-dimensional gait analysis before and after a 30-min treadmill walk. Peak knee flexion angle and extensor moment were compared between groups and before and after the 30-min walk. RESULTS: Comparing groups at baseline, peak knee flexion angle and peak knee extensor moment were not statistically significantly different between groups. After the 30-min walk, peak knee flexion angle and extensor moment increased slightly in both groups. CONCLUSIONS: Smaller, not larger, peak knee flexion angle and extensor moment during walking have been associated with increased risk of PFP. Therefore, sedentary and active young women can walk for 30 min without further detrimental changes to walking biomechanics that may increase their risk of PFP.

The influence of surface and speed on biomechanical external loads obtained from wearable devices in rearfoot strike runners.

External load variables such as peak tibial acceleration (PTA), peak vertical ground reaction forces (GRF) and its instantaneous vertical loading rate (IVLR) may contribute to running injuries although evidence is conflicting given the influence of training load and tissue health on injuries. These variables are influenced by footwear, speed, surface and foot strike pattern during running. The purpose of this study was to assess the influence of four surfaces and two running speeds on external load variables in rearfoot strike (RFS) runners. Twelve RFS runners (confirmed with sagittal foot contact angle) completed a 2-min running bout on a treadmill and 50-m running bouts over the three surfaces (pavement, rubber track and grass) in standardised shoes at their preferred speed and 20% faster. PTA and vertical GRFs were collected using inertial measurement units and in-shoe force insoles. No interaction or surface effects were observed (p > 0.017). The faster speed produced greater axial PTA (+19.2%; p < 0.001), resultant PTA (+20.7%; p < 0.001), peak vertical GRF (+6.6%; p = 0.002) and IVLR (+16.5%; p < 0.001). These findings suggest that surface type does not influence PTA, peak vertical GRF and IVLR but that running faster increases the magnitude of these external loads regardless of surface type in RFS runners.

Workload and Noncontact Musculoskeletal Injury in Collegiate Swimmers: A Prospective Cohort Study.

CONTEXT: Swimmers are known for experiencing high training loads and a high incidence of overuse injuries, but few researchers have investigated the relationship between the two at the collegiate level. OBJECTIVE: To determine the association between workload and noncontact musculoskeletal injury in collegiate swimmers. DESIGN: Prospective cohort study. SETTING: College natatorium. PATIENTS OR OTHER PARTICIPANTS: A total of 37 National Collegiate Athletic Association Division III swimmers, 26 uninjured (age = 19 years [interquartile range = 3 years], height = 175 ± 11 cm, mass = 70.2 ± 10 kg) and 11 injured (age = 19 years [interquartile range = 3 years], height = 173 ± 9 cm, mass = 69.4 ± 13.5 kg) individuals. MAIN OUTCOME MEASURE(S): Logistic regression using generalized estimating equations was conducted to calculate odds ratios (ORs) with 95% CIs for injury relative to high workloads and high acute:chronic workload ratio (ACWRs). Injury rates for several ranges of workloads and ACWRs were also calculated. RESULTS: A total of 11 participants (29.7%) sustained 12 injuries, with 7 injuries occurring during the participants' winter training trip. Injury was associated with high acute workloads (OR = 27.1; 95% CI = 8.2, 89.8) and high ACWRs (OR = 25.1; 95% CI = 7.7, 81.4) but not high chronic (OR = 2.6; 95% CI = 0.3, 20.0) or overall (OR = 1.00; 95% CI = 0.99, 1.01) workloads. High acute workloads (>37.2 km/wk) and ACWRs (>1.56) increased the injury rate from ≤1% to 15% and 14%, respectively, compared with all lower acute workloads and ACWRs. CONCLUSIONS: Collegiate swimmers tolerated high workloads spread out during the season. However, caution should be used when prescribing high acute workloads and high ACWRs (eg, winter training trip) because of the increased odds of injury.

Within-Session Reliability and Minimum Detectable Differences for Discrete Lower-Extremity Angles and Moments During Walking.

Differences in walking biomechanics between groups or conditions should be greater than the measurement error to be considered meaningful. Reliability and minimum detectable differences (MDDs) have not been determined for lower-extremity angles and moments during walking within a session, as needed for interpreting differences in cross-sectional studies. Thus, the purpose of this study was to determine within-session reliability and MDDs for peak ankle, knee, and hip angles and moments during walking. Three-dimensional gait analysis was used to record walking at 1.25 m/s (±5%) in 18 men, 18-50 years of age. Peak angles and moments were calculated for 2 sets of 3 trials. Intraclass correlation coefficients (3, 3) were used to determine within-session reliability. In addition, MDDs were calculated. Within-session reliability was good to excellent for all variables. The MDDs ranged from 0.9° to 3.6° for joint angles and 0.06 to 0.15 N·m/kg for joint moments. Within-session reliability for peak ankle, knee, and hip angles and moments was better than the between-session reliability reported previously. Overall, our MDDs were similar or smaller than those previously reported for between-session reliability. The authors recommend using these MDDs to aid in the interpretation of cross-sectional comparisons of lower-extremity biomechanics during walking in healthy men.

Detection of foot contact in treadmill running with inertial and optical measurement systems.

In running assessments, biomechanics of the stance phase are often measured to understand external loads applied to the body. Identifying time of initial foot contact can be challenging in runners with different strike patterns. Peak downward velocity of the pelvis (PDVP) has been validated in a laboratory setting to detect initial contact. Inertial measurement units (IMUs) allow measurements of kinematic variables outside laboratory settings. The aim of this study was to validate the PDVP method using an inertial and optical motion capture system to detect initial contact at different speeds and foot strike patterns compared to the force sensing criterion. Twenty healthy runners ran for two minutes at 11, 13, and 15 km/h on a force-instrumented treadmill. 3D kinematics were obtained from an optical motion capture system and an 8-sensor inertial system. A generalized estimating equation showed no effect of footstrike pattern on the time difference (offset) between initial contact based on an inertial or optical system and the force sensing criterion. There was a significant main effect of speed on offset, in which offsets decreased with higher speeds. There was no interaction effect of speed and foot strike pattern on the offsets. Offsets ranged from 21.7 ± 0.2 ms for subjects running at 15 km/h (inertial versus force sensing criterion) to 27.2 ± 0.1 ms for subjects running at 11 km/h (optical versus force sensing criterion). These findings support the validity of the PDVP method obtained from optical and inertial systems to detect initial contact in different footstrike patterns and at different running speeds.

Weak associations between hip adduction angle and hip abductor muscle activity during running.

Hip abductor muscle strengthening is often prescribed to reduce the peak hip adduction angle in runners with overuse knee injury. However, no evidence exists associating greater isometric hip abductor muscle strength with smaller peak hip adduction angle during running. Beyond muscle strength, muscle activation patterns may play an important role in controlling joint movement during running. Therefore, the purpose of this investigation was to determine if associations existed among hip adduction angle, hip abductor muscle activity, and isometric hip abductor muscle strength. Twenty-five currently healthy female runners participated. Average gluteus medius muscle activity and tensor fascia lata muscle activity were determined during hip abductor maximal voluntary isometric contractions. Three-dimensional kinematics and hip abductor muscle activity were collected during treadmill running. Dependent variables were analyzed via Pearson product moment correlations. Multi-variable linear regression determined muscle activity's and strength's contributions to the peak hip adduction angle. A fair positive correlation was observed between the peak hip adduction angle and average tensor fascia lata muscle activity magnitude. Additionally, there was a moderate negative correlation between isometric hip abductor muscle strength and average gluteus medius muscle activity magnitude. Tensor fascia lata activity magnitude accounted for the most variance of the peak hip adduction angle. This study adds to the literature which indicates a lack of association between isometric hip abductor muscle strength and peak hip adduction angle in healthy runners. Factors other than hip abductor muscle strength and activation may account for more of the variance in peak hip adduction angles among runners.

Tibial Acceleration Reliability and Minimal Detectable Difference During Overground and Treadmill Running.

Measurements of tibial acceleration during running must be reliable to ensure valid results and reduce errors. The purpose of this study was to determine the reliability and minimal detectable difference (MDD) of peak axial and peak resultant tibial acceleration during overground and treadmill running. The authors also compared reliability and MDDs when peak tibial accelerations were determined by averaging 5 or 10 trials. Tibial acceleration was measured during overground and treadmill running of 19 participants using a lightweight accelerometer mounted to the tibia. Peak axial and peak resultant tibial accelerations were determined for each trial. Intraclass correlation coefficients determined within-session reliability, and MDDs were also calculated. Within-session reliability was excellent for all conditions (intraclass correlation coefficients = .95-.99). The MDDs ranged from 0.6 to 1.4 g for peak axial acceleration and from 1.6 to 2.0 g for peak resultant acceleration and were lowest for peak axial tibial acceleration during overground running. Averaging 10 trials did not improve reliability compared to averaging 5 trials but did result in small reductions in MDDs. For peak axial tibial acceleration only, lower MDDs indicate that overground running may be the better option for detecting small differences.

Relationships of hip abductor strength, neuromuscular control, and hip width to femoral length ratio with peak hip adduction angle in healthy female runners.

A large peak hip adduction angle during running is a risk factor for several overuse injuries in women. The purpose of this study was to determine if female runners with a large peak hip adduction angle have differences in eccentric hip abductor muscle strength, hip neuromuscular control, and/or hip width to femoral length ratio (HW:FL) compared to those with a small angle. Hip adduction during running, hip strength, hip control, and HW:FL were measured in sixty healthy female runners (1.66 ± 0.06 m; 63.2 ± 8.3 kg; 27 ± 6 years). Data from twenty runners with the largest and twenty with the smallest peak hip adduction angles were analysed. Between-group differences in hip strength, control, and HW:FL were determined using independent t-tests (p < 0.05). Variables that were significantly different between groups were entered into a regression model. Runners in both groups had similar hip strength (p = 0.90) and control (p = 0.65). HW:FL was greater in the large peak angle group (p = 0.04), but only explained a small amount of peak hip adduction angle variance for all sixty runners (R2 = 0.05). Alarge peak hip adduction angle in some healthy female runners may simply be instinctive as there were no deficiencies in the strength or neuromuscular control constructs assessed.

Foot contact identification using a single triaxial accelerometer during running.

The analysis of in-field biomechanics data typically requires the identification of foot contact. Existing techniques to identify foot contact using accelerometers offer a viable option for identifying foot contact in the field. However, these techniques often require the placement of additional accelerometers or the identification of impact peaks, which can be difficult when peaks are low. Using resultant tibial acceleration to identify foot contact may overcome these limitations. The purpose of this study was to develop a new technique for identifying time of foot contact during rearfoot strike running from a single triaxial accelerometer placed on the distal tibia. Additionally, we sought to establish the concurrent validity of this new technique. An algorithm to identify foot contact from a local minimum in the resultant tibial acceleration waveform was developed and tested in nineteen rearfoot strike runners. Foot contact determined from the resultant tibial acceleration occurred 2.3 ± 4.7 ms earlier than foot contact determined from vertical ground reaction force, with 95% limits of agreement of -6.8 to 11.5 ms. The difference between the two methods was less than 10 ms for 183 out of 190 foot contacts. These findings compare favorably to previous techniques for identifying foot contact using accelerometers. Additionally, this technique can also be used when peak tibial accelerations are low. We recommend this technique to identify foot contacts in the field, particularly when some peak values are expected to be low.

Tibial Acceleration during Running Is Higher in Field Testing Than Indoor Testing.

Tibial acceleration is frequently measured in runners, and recent advances in wireless technology have led to field studies measuring tibial acceleration outside the laboratory. However, it is unknown whether laboratory and field measures of tibial acceleration differ within runners. In addition, the relationship between peak axial acceleration and the more recent measure peak resultant tibial acceleration has not been determined. PURPOSE: This study aimed to determine whether laboratory and field measures of tibial acceleration are comparable, and whether peak axial and peak resultant tibial acceleration are interchangeable. METHODS: Nineteen healthy rearfoot striking runners between 18 and 45 yr of age participated. A precision accelerometer was aligned with the vertical axis of the distal tibia and firmly attached. Data were collected in the following conditions during running at 3.0 m·s ± 5%: traditional overground laboratory gait analysis contacting force plates, treadmill, outdoor grass, and outdoor sidewalk. Acceleration data were filtered and normalized to gravity. Peaks for variables of interest were extracted from the first 40% of stride for 10 trials per condition. Differences among conditions were determined. RESULTS: Peak positive acceleration was lower in laboratory and treadmill compared with grass and sidewalk conditions. However, laboratory and treadmill were similar in magnitude, as were grass and sidewalk. Peak resultant acceleration was consistently higher than peak axial acceleration, with the same pattern among conditions. Laboratory acceleration measures explained at best only half of the variance in the field conditions and did not explain the variance for grass. CONCLUSION: Tibial impact acceleration magnitude is influenced by testing procedures in runners. These findings support measuring tibial impact acceleration in the field to determine new metrics associated with injury.

Relationship between iliotibial band syndrome and hip neuromechanics in women runners.

BACKGROUND: Atypical frontal plane hip kinematics are associated with iliotibial band syndrome in women runners. Gluteus medius is the primary muscle controlling the hip adduction angle during the loading response of stance. It is unclear if differences exist in gluteus medius activity magnitude and activity duration between runners with previous iliotibial band syndrome and controls. Furthermore, hip neuromechanics may change after a prolonged run. RESEARCH QUESTION: Do differences exist in the hip adduction angle and gluteus medius activity between women with previous iliotibial band syndrome and controls at the beginning and end of a 30-minute moderate paced treadmill run? METHODS: Thirty women participated (n = 15 controls). Lower extremity kinematics and gluteus medius activity were recorded at the start and end of a 30-minute treadmill run at participants' self-selected pace. Hip kinematics and gluteus medius activity were analyzed via separate two-way (group x time) mixed-model analysis of variance with time as the repeated measure. RESULTS: Hip neuromechanics were similar at the start and end of a 30-minute treadmill run in women with previous iliotibial band syndrome and controls. However, hip adduction excursion was less in women with previous iliotibial band syndrome compared to controls. Average gluteus medius activity magnitude and activity duration were not significantly different between groups. SIGNIFICANCE: These findings support the growing body of literature that smaller hip adduction motion is related to previous iliotibial band syndrome in women. Regardless of injury history, gluteus medius activity was similar between groups during the loading phase of stance.

The hip control test is a valid and reliable measure of hip neuromuscular control.

Insufficient hip neuromuscular control may contribute to non-contact sport injuries. However, the current evaluative test of hip neuromuscular control, the single-leg squat, requires hip abductor muscle strength to complete. The purpose of this study was to develop the hip control test (HCT) and determine the test's reliability and construct validity. Nineteen healthy adults visited the laboratory twice. The HCT is a 10-s test of reciprocal toe-tapping accuracy. Both automated and manual HCT ratings were recorded simultaneously during each visit. Additionally, eccentric hip abductor torque was measured. HCT reliability was assessed with intra-class correlation coefficients (ICC). Agreement between automated and manual ratings was determined with Bland-Altman plots. Construct validity was established if HCT performance significantly decreased with a secondary cognitive task (p < 0.05). Bivariate regression determined the relationship between HCT performance and eccentric hip abductor torque. Automated and manual HCT ratings both had moderate reliability (ICC = 0.72) and yielded similar results (limits of agreement = -1 to 2 taps). The HCT had construct validity (p = 0.001), and no correlation with hip abductor muscle strength (r = 0.213). Thus, the HCT is a reliable and valid test. The HCT is simple to administer and measures hip neuromuscular control separately from strength.

Influence of Previous Iliotibial Band Syndrome on Coordination Patterns and Coordination Variability in Female Runners.

It is unknown if female runners that have sustained multiple iliotibial band syndrome occurrences run differently compared to runners that developed the injury once or controls. Therefore, the purpose of this study was to determine if differences existed in coordination patterns and coordination variability among female runners with recurrent iliotibial band syndrome, one iliotibial band syndrome occurrence, and controls. Overground running trials were collected for 36 female runners (n = 18 controls). Lower extremity coordination patterns were examined during running via a vector coding analysis. Coordination variability was calculated via the ellipse area method. Separate one-way (group) Kruskal-Wallis tests were performed to compare each coordination pattern and coordination variability. Lower extremity coordination between frontal plane hip - transverse plane hip, frontal plane pelvis - frontal plane thigh, and frontal plane thigh - transverse plane shank was similar among groups and so may not be related to the risk of iliotibial band syndrome. Runners with one iliotibial band syndrome occurrence demonstrated greater coordination variability for two of three couplings compared to both controls and runners with recurrent iliotibial band syndrome. Thus, the number of previous injury episodes may influence coordination variability in female runners with a history of iliotibial band syndrome.

Reducing Impact Loading in Runners: A One-Year Follow-up.

Increased vertical impact loading during running has been associated with a variety of running related injuries including stress fractures, patellofemoral pain, and plantar fasciitis. PURPOSE: The purpose of this study was to examine the acute and long-term effect of a gait retraining program aimed at teaching runners with high impact loading to run softer. METHODS: Nineteen runners with high tibial shock (TS) first underwent a control period of eight sessions of treadmill running over 2 wk, progressing from 15 to 30 min. This was followed by eight sessions of gait retraining over 2 wk using the identical treadmill protocol. Real-time feedback of TS was provided as the participant ran. Feedback was gradually removed during the last four sessions. Variables of interest included peak TS, vertical impact peak and vertical average loading rate, and vertical instantaneous loading rate. These variables were assessed at intervals following the retraining and at a 1-yr follow-up. RESULTS: All variables of interest were significantly reduced post-retraining (P < 0.001). TS was reduced by 32%, vertical impact peak by 21%, vertical instantaneous loading rate by 27%, and vertical average loading rate by 25%. All variables continued to be significantly reduced at a 1-yr follow-up. CONCLUSIONS: Impact loading can be reduced through gait retraining and the results persist at least 1 yr. As impact loading is associated with injury, this simple intervention may provide a powerful method of reducing musculoskeletal injury risk in runners.

Walking velocity and step length adjustments affect knee joint contact forces in healthy weight and obese adults.

Knee osteoarthritis is a major public health problem and adults with obesity are particularly at risk. One approach to alleviating this problem is to reduce the mechanical load at the joint during daily activity. Adjusting temporospatial parameters of walking could mitigate cumulative knee joint mechanical loads. The purpose of this study was to determine how adjustments to velocity and step length affects knee joint loading in healthy weight adults and adults with obesity. We collected three-dimensional gait analysis data on 10 adults with a normal body mass index and 10 adults with obesity during over ground walking in nine different conditions. In addition to preferred velocity and step length, we also conducted combinations of 15% increased and decreased velocity and step length. Peak tibiofemoral joint impulse and knee adduction angular impulse were reduced in the decreased step length conditions in both healthy weight adults (main effect) and those with obesity (interaction effect). Peak knee joint adduction moment was also reduced with decreased step length, and with decreased velocity in both groups. We conclude from these results that adopting shorter step lengths during daily activity and when walking for exercise can reduce mechanical stimuli associated with articular cartilage degenerative processes in adults with and without obesity. Thus, walking with reduced step length may benefit adults at risk for disability due to knee osteoarthritis. Clinical Significance: Adopting a shorter step length during daily walking activity may reduce knee joint loading and thus benefit those at risk for knee cartilage degeneration. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2679-2686, 2018.

Intratester Reliability and Construct Validity of a Hip Abductor Eccentric Strength Test.

CONTEXT: Side-lying hip abductor strength tests are commonly used to evaluate muscle strength. In a "break" test, the tester applies sufficient force to lower the limb to the table while the patient resists. The peak force is postulated to occur while the leg is lowering, thus representing the participant's eccentric muscle strength. However, it is unclear whether peak force occurs before or after the leg begins to lower. OBJECTIVES: To determine intrarater reliability and construct validity of a hip abductor eccentric strength test. DESIGN: Intrarater reliability and construct validity study. PARTICIPANTS: Twenty healthy adults (26 [6] y; 1.66 [0.06] m; 62.2 [8.0] kg) made 2 visits to the laboratory at least 1 week apart. MAIN OUTCOME MEASURES: During the hip abductor eccentric strength test, a handheld dynamometer recorded peak force and time to peak force, and limb position was recorded via a motion capture system. Intrarater reliability was determined using intraclass correlation, SEM, and minimal detectable difference. Construct validity was assessed by determining if peak force occurred after the start of the lowering phase using a 1-sample t test. RESULTS: The hip abductor eccentric strength test had substantial intrarater reliability (intraclass correlation(3,3) = .88; 95% confidence interval, .65-.95), SEM of 0.9 %BWh, and a minimal detectable difference of 2.5 %BWh. Construct validity was established as peak force occurred 2.1 (0.6) seconds (range: 0.7-3.7 s) after the start of the lowering phase of the test (P ≤ .001). CONCLUSION: The hip abductor eccentric strength test is a valid and reliable measure of eccentric muscle strength. This test may be used clinically to assess changes in eccentric muscle strength over time.

Sound-Intensity Feedback During Running Reduces Loading Rates and Impact Peak.

Study Design Controlled laboratory study, within-session design. Background Gait retraining has been proposed as an effective intervention to reduce impact loading in runners at risk of stress fractures. Interventions that can be easily implemented in the clinic are needed. Objective To assess the immediate effects of sound-intensity feedback related to impact during running on vertical impact peak, peak vertical instantaneous loading rate, and vertical average loading rate. Methods Fourteen healthy, college-aged runners who ran at least 9.7 km/wk participated (4 male, 10 female; mean ± SD age, 23.7 ± 2.0 years; height, 1.67 ± 0.08 m; mass, 60.9 ± 8.7 kg). A decibel meter provided real-time sound-intensity feedback of treadmill running via an iPad application. Participants were asked to reduce the sound intensity of running while receiving continuous feedback for 15 minutes, while running at their self-selected preferred speed. Baseline and follow-up ground reaction force data were collected during overground running at participants' self-selected preferred running speed. Results Dependent t tests indicated a statistically significant reduction in vertical impact peak (1.56 BW to 1.13 BW, P≤.001), vertical instantaneous loading rate (95.48 BW/s to 62.79 BW/s, P = .001), and vertical average loading rate (69.09 BW/s to 43.91 BW/s, P≤.001) after gait retraining, compared to baseline. Conclusion The results of the current study support the use of sound-intensity feedback during treadmill running to immediately reduce loading rate and impact force. The transfer of within-session reductions in impact peak and loading rates to overground running was demonstrated. Decreases in loading were of comparable magnitude to those observed in other gait retraining methods. J Orthop Sports Phys Ther 2017;47(8):565-569. Epub 6 Jul 2017. doi:10.2519/jospt.2017.7275.