Increasing running step rate reduces patellofemoral joint forces.

PURPOSE: Increasing step rate has been shown to elicit changes in joint kinematics and kinetics during running, and it has been suggested as a possible rehabilitation strategy for runners with patellofemoral pain. The purpose of this study was to determine how altering step rate affects internal muscle forces and patellofemoral joint loads, and then to determine what kinematic and kinetic factors best predict changes in joint loading. METHODS: We recorded whole body kinematics of 30 healthy adults running on an instrumented treadmill at three step rate conditions (90%, 100%, and 110% of preferred step rate). We then used a 3-D lower extremity musculoskeletal model to estimate muscle, patellar tendon, and patellofemoral joint forces throughout the running gait cycles. In addition, linear regression analysis allowed us to ascertain the relative influence of limb posture and external loads on patellofemoral joint force. RESULTS: Increasing step rate to 110% of the preferred reduced peak patellofemoral joint force by 14%. Peak muscle forces were also altered as a result of the increased step rate with hip, knee, and ankle extensor forces, and hip abductor forces all reduced in midstance. Compared with the 90% step rate condition, there was a concomitant increase in peak rectus femoris and hamstring loads during early and late swing, respectively, at higher step rates. Peak stance phase knee flexion decreased with increasing step rate and was found to be the most important predictor of the reduction in patellofemoral joint loading. CONCLUSION: Increasing step rate is an effective strategy to reduce patellofemoral joint forces and could be effective in modulating biomechanical factors that can contribute to patellofemoral pain.

Computational models predict larger muscle tissue strains at faster sprinting speeds.

INTRODUCTION: Proximal biceps femoris musculotendon strain injury has been well established as a common injury among athletes participating in sports that require sprinting near or at maximum speed; however, little is known about the mechanisms that make this muscle tissue more susceptible to injury at faster speeds. PURPOSE: This study aimed to quantify localized tissue strain during sprinting at a range of speeds. METHODS: Biceps femoris long head (BFlh) musculotendon dimensions of 14 athletes were measured on magnetic resonance (MR) images and used to generate a finite-element computational model. The model was first validated through comparison with previous dynamic MR experiments. After validation, muscle activation and muscle-tendon unit length change were derived from forward dynamic simulations of sprinting at 70%, 85%, and 100% maximum speed and used as input to the computational model simulations. Simulations ran from midswing to foot contact. RESULTS: The model predictions of local muscle tissue strain magnitude compared favorably with in vivo tissue strain measurements determined from dynamic MR experiments of the BFlh. For simulations of sprinting, local fiber strain was nonuniform at all speeds, with the highest muscle tissue strain where injury is often observed (proximal myotendinous junction). At faster sprinting speeds, increases were observed in fiber strain nonuniformity and peak local fiber strain (0.56, 0.67, and 0.72 for sprinting at 70%, 85%, and 100% maximum speed). A histogram of local fiber strains showed that more of the BFlh reached larger local fiber strains at faster speeds. CONCLUSIONS: At faster sprinting speeds, peak local fiber strain, fiber strain nonuniformity, and the amount of muscle undergoing larger strains are predicted to increase, likely contributing to the BFlh muscle's higher injury susceptibility at faster speeds.

Low back and hip pain in a postpartum runner: applying ultrasound imaging and running analysis.

STUDY DESIGN: Case report. BACKGROUND: Postpartum low back and hip dysfunction may be caused by an incomplete recovery of abdominal musculature and impaired neuromuscular control. The purpose of this report is to describe the management of a postpartum runner with hip and low back pain through exercise training via ultrasound imaging (USI) biofeedback combined with running-form modification. CASE DESCRIPTION: A postpartum runner with hip and low back pain underwent dynamic lumbar stabilization training with USI biofeedback and running-form modification to reduce mechanical loading. Muscle thickness of transversus abdominis and internal oblique was measured with USI preintervention and 7 weeks after completion of the intervention. Additionally, 3-dimensional lower extremity joint motions, moments, and powers were calculated during treadmill running. OUTCOMES: The patient's pain with running decreased from a constant 9/10 (0, no pain; 10, worst pain) to an occasional 3/10 posttreatment. Transversus abdominis muscle thickness increased 6.3% during the abdominal drawing-in maneuver and 27.0% during the abdominal drawing-in maneuver with straight leg raise. Changes were also noted in the internal oblique. These findings corresponded to improved lumbopelvic control: pelvic list and axial rotation during running decreased 38% and 36%, respectively. The patient's running volume returned to preinjury levels (8.1-9.7 km, 3 days per week) with no hip pain and minimal low back pain, and she successfully completed her goal of running a half-marathon. DISCUSSION: The successful outcomes of this case support the consideration of dynamic lumbar stabilization exercises, USI biofeedback, and running-form modification in postpartum runners with lumbopelvic dysfunction. LEVEL OF EVIDENCE: Therapy, level 4.

Changes in muscle activation patterns when running step rate is increased.

Running with a step rate 5-10% greater than one's preferred can substantially reduce lower extremity joint moments and powers, and has been suggested as a possible strategy to aid in running injury management. The purpose of this study was to examine how neuromuscular activity changes with an increase in step rate during running. Forty-five injury-free, recreational runners participated in this study. Three-dimensional motion, ground reaction forces, and electromyography (EMG) of 8 muscles (rectus femoris, vastus lateralis, medial gastrocnemius, tibialis anterior, medial and lateral hamstrings, and gluteus medius and maximus) were recorded as each subject ran at their preferred speed for three different step rate conditions: preferred, +5% and +10% of preferred. Outcome measures included mean normalized EMG activity for each muscle at specific periods during the gait cycle. Muscle activities were found to predominantly increase during late swing, with no significant change in activities during the loading response. This increased muscle activity in anticipation of foot-ground contact likely alters the landing posture of the limb and the subsequent negative work performed by the joints during stance phase. Further, the increased activity observed in the gluteus maximus and medius suggests running with a greater step rate may have therapeutic benefits to those with anterior knee pain.

Effects of step rate manipulation on joint mechanics during running.

PURPOSE: the objective of this study was to characterize the biomechanical effects of step rate modification during running on the hip, knee, and ankle joints so as to evaluate a potential strategy to reduce lower extremity loading and risk for injury. METHODS: three-dimensional kinematics and kinetics were recorded from 45 healthy recreational runners during treadmill running at constant speed under various step rate conditions (preferred, ± 5%, and ± 10%). We tested our primary hypothesis that a reduction in energy absorption by the lower extremity joints during the loading response would occur, primarily at the knee, when step rate was increased. RESULTS: less mechanical energy was absorbed at the knee (P < 0.01) during the +5% and +10% step rate conditions, whereas the hip (P < 0.01) absorbed less energy during the +10% condition only. All joints displayed substantially (P < 0.01) more energy absorption when preferred step rate was reduced by 10%. Step length (P < 0.01), center of mass vertical excursion (P < 0.01), braking impulse (P < 0.01), and peak knee flexion angle (P < 0.01) were observed to decrease with increasing step rate. When step rate was increased 10% above preferred, peak hip adduction angle (P < 0.01) and peak hip adduction (P < 0.01) and internal rotation (P < 0.01) moments were found to decrease. CONCLUSION: we conclude that subtle increases in step rate can substantially reduce the loading to the hip and knee joints during running and may prove beneficial in the prevention and treatment of common running-related injuries.

Hamstring musculotendon dynamics during stance and swing phases of high-speed running.

INTRODUCTION: Hamstring strain injuries are common in sports that involve high-speed running. It remains uncertain whether the hamstrings are susceptible to injury during late swing phase, when the hamstrings are active and lengthening, or during stance, when contact loads are present. In this study, we used forward dynamic simulations to compare hamstring musculotendon stretch, loading, and work done during stance and swing phases of high-speed running. METHODS: Whole-body kinematics, EMG activities, and ground reactions were collected as 12 subjects ran on an instrumented treadmill at speeds ranging from 80% to 100% of maximum (avg max speed = 7.8 m·s(-1)). Subject-specific simulations were then created using a whole-body musculoskeletal model that included 52 Hill-type musculotendon units acting about the hip and the knee. A computed muscle control algorithm was used to determine muscle excitation patterns that drove the limb to track measured hip and knee sagittal plane kinematics, with measured ground reactions applied to the limb. RESULTS: The hamstrings lengthened under load from 50% to 90% of the gait cycle (swing) and then shortened under load from late swing through stance. Although peak hamstring stretch was invariant with speed, lateral hamstring (biceps femoris) loading increased significantly with speed and was greater during swing than stance at the fastest speed. The biarticular hamstrings performed negative work on the system only during swing phase, with the amount of negative work increased significantly with speed. CONCLUSION: We concluded that the large inertial loads during high-speed running appear to make the hamstrings most susceptible to injury during swing phase. This information is relevant for scientifically establishing muscle injury prevention and rehabilitation programs.

Computational techniques for using insole pressure sensors to analyse three-dimensional joint kinetics.

This study evaluated the feasibility of using insole pressure sensors together with whole body dynamics to analyse joint kinetics while running. Local affine transformations of shoe kinematics were first used to track the position of insole sensors during locomotion. Centre of pressure estimates derived from the insoles were within 10 mm of forceplate measures through much of stance, while vertical force estimates were within 15% of peak forceplate recordings. Insole data were then coupled with a least squares whole body dynamic model to obtain shear force estimates that were comparable to forceplate records during running. We demonstrated that these techniques provide a viable approach for analysing joint kinetics when running on uninstrumented surfaces.

Hamstring strain injuries: recommendations for diagnosis, rehabilitation, and injury prevention.

UNLABELLED: Hamstring strain injuries remain a challenge for both athletes and clinicians, given their high incidence rate, slow healing, and persistent symptoms. Moreover, nearly one third of these injuries recur within the first year following a return to sport, with subsequent injuries often being more severe than the original. This high reinjury rate suggests that commonly utilized rehabilitation programs may be inadequate at resolving possible muscular weakness, reduced tissue extensibility, and/or altered movement patterns associated with the injury. Further, the traditional criteria used to determine the readiness of the athlete to return to sport may be insensitive to these persistent deficits, resulting in a premature return. There is mounting evidence that the risk of reinjury can be minimized by utilizing rehabilitation strategies that incorporate neuromuscular control exercises and eccentric strength training, combined with objective measures to assess musculotendon recovery and readiness to return to sport. In this paper, we first describe the diagnostic examination of an acute hamstring strain injury, including discussion of the value of determining injury location in estimating the duration of the convalescent period. Based on the current available evidence, we then propose a clinical guide for the rehabilitation of acute hamstring injuries, including specific criteria for treatment progression and return to sport. Finally, we describe directions for future research, including injury-specific rehabilitation programs, objective measures to assess reinjury risk, and strategies to prevent injury occurrence. LEVEL OF EVIDENCE: Diagnosis/therapy/prevention, level 5.

Gender differences in walking and running on level and inclined surfaces.

BACKGROUND: Gender differences in kinematics during running have been speculated to be a contributing factor to the lower extremity injury rate disparity between men and women. Specifically, increased non-sagittal motion of the pelvis and hip has been implicated; however it is not known if this difference exists under a variety of locomotion conditions. The purpose of this study was to characterize gender differences in gait kinematics and muscle activities as a function of speed and surface incline and to determine if lower extremity anthropometrics contribute to these differences. METHODS: Whole body kinematics of 34 healthy volunteers were recorded along with electromyography of muscles on the right lower limb while each subject walked at 1.2, 1.5, and 1.8m/s and ran at 1.8, 2.7, and 3.6m/s with surface inclinations of 0%, 10%, and 15% grade. Joint angles and muscle activities were compared between genders across each speed-incline condition. Pelvis and lower extremity segment lengths were also measured and compared. FINDINGS: Females displayed greater peak hip internal rotation and adduction, as well as gluteus maximus activity for all conditions. Significant interactions (speed-gender, incline-gender) were present for the gluteus medius and vastus lateralis. Hip adduction during walking was moderately correlated to the ratio of bi-trochanteric width to leg length. INTERPRETATION: Our findings indicate females display greater non-sagittal motion. Future studies are needed to better define the relationship of these differences to injury risk.

The effect of speed and influence of individual muscles on hamstring mechanics during the swing phase of sprinting.

The purpose of this study was to characterize the effect of speed and influence of individual muscles on hamstring stretch, loading, and work during the swing phase of sprinting. We measured three-dimensional kinematics and electromyography (EMG) activities of 19 athletes sprinting on a treadmill at speeds ranging from 80% to 100% of maximum speed. We then generated muscle-actuated forward dynamic simulations of swing and double float phases of the sprinting gait cycle. Simulated lower extremity joint angles and model predicted excitations were similar to measured quantities. Swing phase simulations were used to characterize the effects of speed on the peak stretch, maximum force, and negative work of the biceps femoris long head (BF), the most often injured hamstring muscle. Perturbations of the double float simulations were used to assess the influence of individual muscles on BF stretch. Peak hamstring musculotendon stretch occurred at approximately 90% of the gait cycle (late swing) and was independent of speed. Peak hamstring force and negative musculotendon work increased significantly with speed (p<0.05). Muscles in the lumbo-pelvic region had greater influence on hamstring stretch than muscles acting about the knee and ankle. In particular, the hip flexors were found to induce substantial hamstring stretch in the opposite limb, with that influence increasing with running speed. We conclude that hamstring strain injury during sprinting may be related to the performance of large amounts of negative work over repeated strides and/or resulting from a perturbation in pelvic muscle coordination that induces excessive hamstring stretch in a single stride.

Neuromusculoskeletal models provide insights into the mechanisms and rehabilitation of hamstring strains.

Neuromusculoskeletal models are used to investigate hamstring mechanics during sprinting. We show that peak hamstring stretch occurs during late swing phase and is invariant with speed, but does depend on tendon compliance and the action of other muscles in the lumbopelvic region. The insights gained are relevant for improving the scientific basis of hamstring strain injury prevention and rehabilitation programs.

Simulation of biceps femoris musculotendon mechanics during the swing phase of sprinting.

INTRODUCTION/PURPOSE: Characterization of hamstring mechanics during sprinting is fundamental to understanding musculotendon injury mechanisms. The objective of this study was to use muscle-actuated forward dynamic simulations to investigate musculotendon mechanics of the biceps femoris long head during the swing phase of sprinting. METHODS: We used a three-dimensional linked segment model with 26 Hill-type musculotendon actuators to simulate swing phase dynamics. Muscle excitations were computed that drove the linked segment model to track measured hip and knee motion of an individual sprinting on a treadmill. The simulations were used to investigate the effect of tendon compliance on the excursions and power development of the muscle and tendinous components of the biceps femoris. RESULTS: The biceps femoris musculotendon complex underwent a stretch-shortening cycle over the latter half of swing phase, with the shortening portion occurring in the final 10% of the gait cycle. Biceps femoris excitation increased markedly between 70 and 80% of the gait cycle and continued through the end of swing. Following the onset of excitation, stretch of the muscle component slowed considerably while the tendon lengthened and stored elastic energy. Simulating the sprinting movement with a more compliant tendon increased tendon elastic energy storage, thereby reducing peak muscle stretch and negative muscle work. CONCLUSIONS: Muscle-actuated forward dynamic simulation provides a powerful approach for investigating biomechanical factors that may contribute to the occurrence of hamstring musculotendon injuries.

Identifying the time of occurrence of a hamstring strain injury during treadmill running: a case study.

BACKGROUND: While hamstring strain injuries are common during sprinting, the mechanisms of injury are not well understood. In this study, we analyzed the running kinematics of an athlete obtained at the time of an acute hamstring strain injury. The purpose was to identify the period of the gait cycle during which the hamstring was likely injured, as well as to characterize the biomechanical conditions associated with the injury. METHODS: A male professional skier injured his right biceps femoris long head while running at 5.36 m/s on a treadmill with a 15% incline. Whole body kinematics were recorded at the time of injury. A linear periodic prediction model was used to determine when individual marker trajectories deviated from a cyclic periodic pattern, indicating the mechanical response to injury. A three-dimensional musculoskeletal model was used to compute joint angles and hamstring musculotendon lengths during the injurious running trial. These data were used with estimates of neuromuscular latencies and electromechanical delays to identify the most likely time period of injury. FINDINGS: Based upon the earliest indications in marker trajectories, a 130 ms period during the late swing phase of the gait cycle was identified as the period of injury. During this period, the biceps femoris reached a peak musculotendon length that was estimated to be 12% beyond the length seen in an upright posture and exceeded the normalized peak length of the medial hamstrings. INTERPRETATION: This case provides quantitative data suggesting that the biceps femoris muscle is susceptible to an lengthening contraction injury during the late swing phase of the running gait cycle.

Hamstring muscle kinematics during treadmill sprinting.

INTRODUCTION/PURPOSE: The objective of this study was to characterize hamstring muscle kinematics during sprinting, so as to provide scientific data to better understand injury mechanisms and differences in injury rates between muscles. METHODS: We conducted three-dimensional motion analyses of 14 athletes performing treadmill sprinting at speeds ranging from 80 to 100% of maximum. Scaled musculoskeletal models were used to estimate hamstring muscle-tendon lengths throughout the sprinting gait cycle for each speed. We tested the hypothesis that the biceps femoris (BF) long head would be stretched a greater amount, relative to its length in an upright posture, than the semitendinosus (ST) and semimembranosus (SM). We also tested the hypothesis that increasing from submaximal to maximal sprinting speed would both increase the magnitude and delay the occurrence of peak muscle-tendon length in the gait cycle. RESULTS: Maximum hamstring lengths occurred during the late swing phase of sprinting and were an average of 7.4% (SM), 8.1% (ST), and 9.5% (BF) greater than the respective muscle-tendon lengths in an upright configuration. Peak lengths were significantly larger in the BF than the ST and SM (P < 0.01), occurred significantly later in the gait cycle at the maximal speed (P < 0.01), but did not increase significantly with speed. Differences in the hip extension and knee flexion moment arms between the biarticular hamstrings account for the intermuscle variations in the peak lengths that were estimated. CONCLUSIONS: We conclude that intermuscle differences in hamstring moment arms about the hip and knee may be a factor contributing to the greater propensity for hamstring strain injuries to occur in the BF muscle.