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.

The effects of gluteus medius and tibialis anterior kinesio taping on postural control, knee kinematics, and knee proprioception in female athletes with dynamic knee valgus.

OBJECTIVES: This study aimed to investigate the effects of Kinesio taping on postural control, kinematics, and knee proprioception in female athletes with dynamic knee valgus (DKV). DESIGN: a single-blind randomized clinical trial. PARTICIPANTS: 40 female athletes between the age of 18 and 28 years with DKV in single-leg drop landing (>13°) participated in this study. They were randomly classified into the Kinesio taping (KT) and placebo control (PC) groups. MAIN OUTCOME MEASURES: All the evaluations and measurements were performed on each subject in the pre-test and post-test stages (with an interval of 72 h). The dynamic balance (Y balance test), proprioception (Knee position sense error), and knee kinematics (flexion and DKV angles) of the subjects were measured, prior and post gluteus medius and tibialis anterior KT. RESULTS: The results of study demonstrate that the DKV angle and knee position sense error significantly decreased and YBT increased in the KT group from pre-test to post-test (p < 0.05). Nevertheless, there was no significant difference in knee flexion angle (p > 0.05). CONCLUSION: The results of the present study indicated that KT improves dynamic balance and proprioception and reduces the DKV angle. Therefore, KT is recommended for female athletes with DKV.

The effects of both jump/land phases and direction on Achilles tendon loading.

BACKGROUND: Athletes in jumping and running sports have a high incidence of Achilles tendon (AT) injuries. We compared AT loading during jumping and landing phases in anteroposterior (AP) and mediolateral (ML) directions. METHODS: Sixteen males (age: 21.6±1.8 years, height: 178.4±6.4 cm, weight: 76.4±11.2 kg) performed single leg AP and ML jump-landings during both propulsive (jump) and braking (land) phases. Inverse dynamics and static optimization were used to determine muscle forces. AT cross sectional area was measured with ultrasound. AT force was divided by cross sectional area to determine stress while strain was determined from previous data. Two-way repeated measures analysis of variance (α=0.05) compared several variables (vertical ground reaction force (VGRF), ankle and knee angle, ankle joint muscle moment arm, external ankle moment arm, AT tendon force, stress, and strain) between movements (jump-landings) and directions (AP/ML). RESULTS: AT loading was higher during jump than land in the ML compared to AP direction. VGRF was higher during land versus jump with no direction effect (AP/ML). An interaction showed a higher VGRF during the AP land and ML jump. The ankle joint moment arm was lower in jump and AP direction at peak tendon stress. External ankle moment arm at peak tendon stress was higher in jump and ML direction with an interaction. A larger external ankle moment arm occurred in ML but the change was less in the jump. CONCLUSIONS: Higher tendon loading occurred during the jump and ML direction. This may provide insight into both injuries and rehabilitation efforts.

Patellar tendon stress between two variations of the forward step lunge.

BACKGROUND: Patellar tendinopathy (PT) or "jumper's knee" is generally found in active populations that perform jumping activities. Graded exposure of patellar tendon stress through functional exercise has been demonstrated to be effective for the treatment of PT. However, no studies have compared how anterior knee displacement variations during the commonly performed forward step lunge (FSL) affect patellar tendon stress. METHODS: Twenty-five subjects (age: 22.69 ± 0.74 years; height: 169.39 ± 6.44 cm; mass: 61.55 ± 9.74 kg) performed 2 variations of an FSL with the anterior knee motion going in front of the toes (FSL-FT) and the knee remaining behind the toes (FSL-BT). Kinematic and kinetic data were used with an inverse-dynamics based static optimization technique to estimate individual muscle forces to determine patellar tendon stress during both lunge techniques. A repeated measures multivariate analysis was used to analyze these data. RESULTS: The peak patellar tendon stress, stress impulse, quadriceps force, knee moment, knee flexion, and ankle dorsiflexion angle were significantly greater (p < 0.001) during the FSL-FT as compared to the FSL-BT. The peak patellar tendon stress rate did not differ between the FSL-FT and FSL-BT. CONCLUSION: The use of an FSL-FT as compared to an FSL-BT increased the load and stress on the patellar tendon. Because a graded exposure of patellar tendon loading with other closed kinetic chain exercises has proven to be effective in treating PT, consideration for the prescription of variations of the FSL and further clinical evaluation of this exercise is warranted in individuals with PT.

Achilles tendon loading during weight bearing exercises.

OBJECTIVE: Compare the estimated Achilles tendon (AT) loading using a musculoskeletal model during commonly performed weight bearing therapeutic exercises. DESIGN: Controlled laboratory study. SETTING: University biomechanics laboratory. PARTICIPANTS: Eighteen healthy males (Age:22.1 ±â€¯1.8 years, height:177.7 ±â€¯8.4 cm, weight = 74.29 ±â€¯11.3 kg). MAIN OUTCOME MEASURE(S): AT loading was estimated during eleven exercises: tandem, Romberg, and unilateral standing, unilateral and bilateral heel raising, unilateral and bilateral jump landing, squat, lunge, walking, and running. Kinematic and kinetic data were recorded at 180 Hz and 1800 Hz respectively. These data were then used in a musculoskeletal model to estimate force in the triceps surae. AT cross-sectional images were measured by ultrasound to determine AT stress. A repeated measure multivariate analysis of variance (α = 0.05) was used on AT loading variables. RESULTS: Squat and unilateral jump landing were the most different in AT stress. Peak AT stress variables were generally greater during more dynamic, unilateral exercises compared to more static, bilateral exercises. CONCLUSIONS: Bilateral, more static exercises resulted in less AT loading and may serve as a progression during the rehabilitation compared to more dynamic, unilateral exercises.

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.

Effect of Posttrial Visual Feedback and Fatigue During Drop Landings on Patellofemoral Joint Stress in Healthy Female Adults.

Patellofemoral pain (PFP) is common in females. Patellofemoral joint stress (PFJS) may be important in the development of PFP. Ground reaction force (GRF) during landing activities may impact PFJS. Our purpose was to determine how healthy females alter their landing mechanics using visual posttrial feedback on their GRF and assess how PFJS changes. Seventeen participants performed a series of drop landings during 3 conditions: baseline, feedback, and postfatigue feedback. The fatigue protocol used repetitive jump squats. Quadriceps force was estimated through inverse-dynamics-based static optimization approach. Then, PFJS was calculated using a musculoskeletal model. Multivariate differences were shown across conditions (P = .01). Univariate tests revealed differences in PFJS (P = .014), knee range of motion (P = .001), and GRF (P = .005). There were no differences in quadriceps force (P = .125). PFJS and GRF decreased from baseline to feedback (P = .002, P = .007, respectively), while PFJS increased from feedback to postfatigue feedback (P = .03). Knee range of motion increased from baseline to feedback (P = .043), then decreased from feedback to postfatigue feedback (P < .001). Visual feedback of GRF may reduce PFJS, but may not effectively transfer to a fatigued state.

EFFECT OF HEEL LIFTS ON PATELLOFEMORAL JOINT STRESS DURING RUNNING.

BACKGROUND: Patellofemoral pain is a debilitating injury for many recreational runners. Excessive patellofemoral joint stress may be the underlying source of pain and interventions often focus on ways to reduce patellofemoral joint stress. PURPOSE: Heel lifts have been used as an intervention within Achilles tendon rehabilitation programs and to address leg length discrepancies. The purpose of this study was to examine the effect of running with heel lifts on patellofemoral joint stress, patellofemoral stress impulse, quadriceps force, step length, cadence, and other related kinematic and spatiotemporal variables. STUDY DESIGN: A repeated-measures research design. METHODS: Sixteen healthy female runners completed five running trials in a controlled laboratory setting with and without 11mm heel lifts inserted in a standard running shoe. Kinetic and kinematic data were used in combination with a static optimization technique to estimate individual muscle forces. These data were inserted into a patellofemoral joint model which was used to estimate patellofemoral joint stress and other variables during running. RESULTS: When running with heel lifts, peak patellofemoral joint stress and patellofemoral stress impulse were reduced by a 4.2% (p=0.049) and 9.3% (p=0.002). Initial center of pressure was shifted anteriorly 9.1% when running with heel lifts (p<0.001) despite all runners utilizing a heel strike pattern. Dorsiflexion at initial contact was reduced 28% (p=0.016) when heel lifts were donned. No differences in step length and cadence (p>0.05) were shown between conditions. CONCLUSIONS: Heel lift use resulted in decreased patellofemoral joint stress and impulse without associated changes in step length or frequency, or other variables shown to influence patellofemoral joint stress. The center of pressure at initial contact was also more anterior using heel lifts. The use of heel lifts may have therapeutic benefits for runners with patellofemoral pain if the primary goal is to reduce patellofemoral joint stress. LEVEL OF EVIDENCE: 3b.

Changes in gluteal muscle forces with alteration of footstrike pattern during running.

Gait retraining is a common form of treatment for running related injuries. Proximal factors at the hip have been postulated as having a role in the development of running related injuries. How altering footstrike affects hip muscles forces and kinematics has not been described. Thus, we aimed to quantify differences in hip muscle forces and hip kinematics that may occur when healthy runners are instructed to alter their foot strike pattern from their habitual rear-foot strike to a forefoot strike. This may gain insight on the potential etiology and treatment methods of running related lower extremity injury. Twenty-five healthy female runners completed a minimum of 10 running trials in a controlled laboratory setting under rear-foot strike and instructed forefoot strike conditions. Kinetic and kinematic data were used in an inverse dynamic based static optimization to estimate individual muscle forces during running. Within subject differences were investigated using a repeated measures multi-variate analysis of variance. Peak gluteus medius and minimus and hamstring forces were reduced while peak gluteus maximus force was increased when running with an instructed forefoot strike pattern. Peak hip adduction, hip internal rotation, and heel-COM distance were also reduced. Therefore, instructing habitual rearfoot strike runners to run with a forefoot strike pattern resulted in changes in peak gluteal and hamstring muscle forces and hip kinematics. These changes may be beneficial to the development and treatment of running related lower extremity injury.

Achilles Tendon Loading During Heel-Raising and -Lowering Exercises.

CONTEXT: Achilles tendinopathies are common injuries during sport participation, although men are more prone to Achilles tendon injuries than women. Heel-raising and -lowering exercises are typically suggested for Achilles tendon rehabilitation. OBJECTIVE: To compare the estimated Achilles tendon loading variables and the ankle range of motion (ROM) using a musculoskeletal model during commonly performed heel-raising and -lowering exercises. DESIGN: Controlled laboratory study. SETTING: University biomechanics laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-one healthy men (age = 21.59 ± 1.92 years, height = 178.22 ± 8.02 cm, mass = 75.81 ± 11.24 kg). INTERVENTION(S): Each participant completed 4 exercises: seated heel raising and lowering, bilateral standing heel raising and lowering, bilateral heel raising and unilateral lowering, and unilateral heel raising and lowering. MAIN OUTCOME MEASURE(S): A repeated-measures multivariate analysis of variance (α = .05) was used to compare Achilles tendon stress, force, and strain and ankle ROM for each exercise. Kinematic data were recorded at 180 Hz with 15 motion-analysis cameras synchronized with kinetic data collected from a force platform sampled at 1800 Hz. These data were then entered in a musculoskeletal model to estimate force in the triceps surae. For each participant, we determined Achilles tendon stress by measuring cross-sectional images using ultrasound. RESULTS: Peak Achilles tendon loading was lowest when performing the seated heel-raising and -lowering exercise and highest when performing the unilateral heel-raising and -lowering exercise. Loading was greater for the unilateral exercise or portions of the exercise that were performed unilaterally. CONCLUSIONS: Bilateral and seated exercises with less weight-bearing force resulted in less Achilles tendon loading. These exercises may serve as progressions during the rehabilitation process before full-body weight-bearing, unilateral exercises are allowed. Ankle ROM did not follow the same order as loading and may need additional monitoring or instruction during rehabilitation.

Comparison of estimates of Achilles tendon loading from inverse dynamics and inverse dynamics-based static optimisation during running.

Tendon stress may be one of the important risk factors for running-related tendon injury. Several methods have been used to estimate Achilles tendon (AT) loading during a human performance such as inverse dynamics (ID) and inverse dynamics-based static optimisation (IDSO). Our purpose was to examine differences between ID and IDSO estimates of AT loading during running. Kinematic data were captured simultaneously with kinetic data. Imaging of the AT cross-sectional area was performed with ultrasound for 17 healthy runners (height: 170.2 ± 6.2 cm, mass: 63.9 ± 11.0 kg, age: 21.8 ± 1.4 years). AT stress, strain, and force were estimated from both ID and IDSO approaches. The two methods resulted in minimal differences (3.6-4.7%) in estimated peak AT stress, strain, and force (P = 0.051-0.054); however, IDSO estimates were greater (32.7-36.8%) during early-stance phase of running (P = 0.000-0.008). This difference in AT load during early-stance may be due to the inability of the ID to account muscle coactivation. The similarity between the peak AT loading for ID and IDSO methods revealed that the advantage of IDSO used to estimate muscle forces had little effect on the ankle plantar flexor peak forces during running. Therefore, the use of IDSO with a higher computational cost compared with ID may not be necessary for estimating AT stress during running.

Plantar loading changes with alterations in foot strike patterns during a single session in habitual rear foot strike female runners.

OBJECTIVES: Characterize plantar loading parameters when habitually rear foot strike (RFS) runners change their pattern to a non-rear foot strike (NRFS). DESIGN: Experimental. SETTING: University biomechanics laboratory. PARTICIPANTS: Twenty three healthy female runners (Age: 22.17 ± 1.64 yrs; Height: 168.91 ± 5.46 cm; Mass: 64.29 ± 7.11 kg). MAIN OUTCOME MEASURES: Plantar loading was measured using an in-sole pressure sensor while running down a 20-m runway restricted to a range of 3.52-3.89 m/s under two conditions, using the runner's typical RFS, and an adapted NRFS pattern. Repeated measures multivariate analysis of variance was performed to detect differences in loading between these two conditions. RESULTS: Force and pressure variables were greater in the forefoot and phalanx in NRFS and greater in the heel and mid foot in RFS pattern, but the total force imposed upon the whole foot and contact time remained similar between conditions. Total peak pressure was higher and contact area was lower during NRFS running. CONCLUSIONS: The primary finding of this investigation is that there are distinctly different plantar loads when changing from a RFS to NRFS during running. So, during a transition from RFS to a NRFS pattern; a period of acclimation should be considered to allow for adaptations to these novel loads incurred on plantar regions of the foot.