Effects of step rate manipulation on joint mechanics during running

Plantar loading and foot-strike pattern changes with speed during barefoot running in those with a natural rearfoot strike pattern while shod

BACKGROUND

Claims of injury reduction related to barefoot running has resulted in interest from the running public; however, its risks are not well understood for those who typically wear cushioned footwear.

OBJECTIVES

Examine how plantar loading changes during barefoot running in a group of runners that ordinarily wear cushioned footwear and demonstrate a rearfoot strike pattern (RFSP) without cueing or feedback alter their foot strike pattern and plantar loading when asked to run barefoot at different speeds down a runway.

METHOD

Forty-one subjects ran barefoot at three different speeds across a pedography platform which collected plantar loading variables for 10 regions of the foot; data were analyzed using two-way mixed multivariate analysis of variance (MANOVA).

RESULTS

A significant foot strike position (FSP)×speed interaction in each of the foot regions indicated that plantar loading differed based on FSP across the different speeds. The RFSP provided the highest total forces across the foot while the pressures displayed in subjects with a non-rearfoot strike pattern (NRFSP) was more similar between each of the metatarsals.

CONCLUSIONS

The majority of subjects ran barefoot with a NRFSP and demonstrated lower total forces and more uniform force distribution across the metatarsal regions. This may have an influence in injuries sustained in barefoot running.

Comparison of minimalist footwear strategies for simulating barefoot running: a randomized crossover study

Possible benefits of barefoot running have been widely discussed in recent years. Uncertainty exists about which footwear strategy adequately simulates barefoot running kinematics. The objective of this study was to investigate the effects of athletic footwear with different minimalist strategies on running kinematics. Thirty-five distance runners (22 males, 13 females, 27.9 ± 6.2 years, 179.2 ± 8.4 cm, 73.4 ± 12.1 kg, 24.9 ± 10.9 km.week^-1) performed a treadmill protocol at three running velocities (2.22, 2.78 and 3.33 m.s^-1) using four footwear conditions: barefoot, uncushioned minimalist shoes, cushioned minimalist shoes, and standard running shoes. 3D kinematic analysis was performed to determine ankle and knee angles at initial foot-ground contact, rate of rear-foot strikes, stride frequency and step length. Ankle angle at foot strike, step length and stride frequency were significantly influenced by footwear conditions (p<0.001) at all running velocities. Posthoc pairwise comparisons showed significant differences (p<0.001) between running barefoot and all shod situations as well as between the uncushioned minimalistic shoe and both cushioned shoe conditions. The rate of rear-foot strikes was lowest during barefoot running (58.6% at 3.33 m.s^-1), followed by running with uncushioned minimalist shoes (62.9%), cushioned minimalist (88.6%) and standard shoes (94.3%). Aside from showing the influence of shod conditions on running kinematics, this study helps to elucidate differences between footwear marked as minimalist shoes and their ability to mimic barefoot running adequately. These findings have implications on the use of footwear applied in future research debating the topic of barefoot or minimalist shoe running.

Influence of step rate and quadriceps load distribution on patellofemoral cartilage contact pressures during running

Interventions used to treat patellofemoral pain in runners are often designed to alter patellofemoral mechanics. This study used a computational model to investigate the influence of two interventions, step rate manipulation and quadriceps strengthening, on patellofemoral contact pressures during running. Running mechanics were analyzed using a lower extremity musculoskeletal model that included a knee with six degree-of-freedom tibiofemoral and patellofemoral joints. An elastic foundation model was used to compute articular contact pressures. The lower extremity model was scaled to anthropometric dimensions of 22 healthy adults, who ran on an instrumented treadmill at 90%, 100% and 110% of their preferred step rate. Numerical optimization was then used to predict the muscle forces, secondary tibiofemoral kinematics and all patellofemoral kinematics that would generate the measured primary hip, knee and ankle joint accelerations. Mean and peak patella contact pressures reached 5.0 and 9.7MPa during the midstance phase of running. Increasing step rate by 10% significantly reduced mean contact pressures by 10.4% and contact area by 7.4%, but had small effects on lateral patellar translation and tilt. Enhancing vastus medialis strength did not substantially affect pressure magnitudes or lateral patellar translation, but did shift contact pressure medially toward the patellar median ridge. Thus, the model suggests that step rate tends to primarily modulate the magnitude of contact pressure and contact area, while vastus medialis strengthening has the potential to alter mediolateral pressure locations. These results are relevant to consider in the design of interventions used to prevent or treat patellofemoral pain in runners.

Increased vertical impact forces and altered running mechanics with softer midsole shoes

To date it has been thought that shoe midsole hardness does not affect vertical impact peak forces during running. This conclusion is based partially on results from experimental data using homogeneous samples of participants that found no difference in vertical impact peaks when running in shoes with different midsole properties. However, it is currently unknown how apparent joint stiffness is affected by shoe midsole hardness. An increase in apparent joint stiffness could result in a harder landing, which should result in increased vertical impact peaks during running. The purpose of this study was to quantify the effect of shoe midsole hardness on apparent ankle and knee joint stiffness and the associated vertical ground reaction force for age and sex subgroups during heel-toe running. 93 runners (male and female) aged 16-75 years ran at 3.33 ± 0.15 m/s on a 30 m-long runway with soft, medium and hard midsole shoes. The vertical impact peak increased as the shoe midsole hardness decreased (mean(SE); soft: 1.70BW(0.03), medium: 1.64BW(0.03), hard: 1.54BW(0.03)). Similar results were found for the apparent ankle joint stiffness where apparent stiffness increased as the shoe midsole hardness decreased (soft: 2.08BWm/º x 100 (0.05), medium: 1.92 BWm/º x 100 (0.05), hard: 1.85 BWm/º x 100 (0.05)). Apparent knee joint stiffness increased for soft (1.06BWm/º x 100 (0.04)) midsole compared to the medium (0.95BWm/º x 100 (0.04)) and hard (0.96BWm/º x 100 (0.04)) midsoles for female participants. The results from this study confirm that shoe midsole hardness can have an effect on vertical impact force peaks and that this may be connected to the hardness of the landing. The results from this study may provide useful information regarding the development of cushioning guidelines for running shoes.

Reliability of video-based quantification of the knee- and hip angle at foot strike during running

INTRODUCTION

In clinical practice, joint kinematics during running are primarily quantified by two-dimensional (2D) video recordings and motion-analysis software. The applicability of this approach depends on the clinicians' ability to quantify kinematics in a reliable manner. The reliability of quantifying knee- and hip angles at foot strike is uninvestigated.

OBJECTIVE

To investigate the intra- and inter-rater reliability within and between days of clinicians' ability to quantify the knee- and hip angles at foot strike during running.

METHODS

Eighteen recreational runners were recorded twice using a clinical 2D video setup during treadmill running. Two blinded raters quantified joint angles on each video twice with freeware motion analysis software (Kinovea 0.8.15).

RESULTS

The range from the lower prediction limit to the upper prediction limit of the 95% prediction interval varied three to eight degrees (within day) and nine to 14 degrees (between day) for the knee angles. Similarly, the hip angles varied three to seven degrees (within day) and nine to 11 degrees (between day).

CONCLUSION

The intra- and inter rater reliability of within and between day quantifications of the knee- and hip angle based on a clinical 2D video setup is sufficient to encourage clinicians to keep using 2D motion analysis techniques in clinical practice to quantify the knee- and hip angles in healthy runners. However, the interpretation should include critical evaluation of the physical set-up of the 2D motion analysis system prior to the recordings and conclusions should take measurement variations (3-8 degrees and 9-14 degrees for within and between day, respectively) into account.

LEVEL OF EVIDENCE

3.

A Survey of Runners' Attitudes Toward and Experiences With Minimally Shod Running

OBJECTIVE

To investigate the characteristics, perceptions, motivating factors, experiences, and injury rates of runners who practice minimally shod running.

DESIGN

Survey.

SETTING

web-based questionnaire.

PARTICIPANTS

Five-hundred sixty-six members of the Chicago Area Runner's Association.

METHODS

A link to a 31-question online survey was e-mailed to members of Chicago Area Runner's Association. Questions covered demographic information, use of minimalist-style running shoes (MSRS), injury rates, and change in pain.

MAIN OUTCOME MEASURES

Use of MSRS, occurrence or improvement of injury/pain, regions of injury/pain, reasons for or for not using MSRS.

RESULTS

One-hundred seventy-five (31%) respondents had practiced minimally shod running, and the most common motivating factor was to decrease injuries and/or pain. Fifty-one respondents (29%) suffered an injury or pain while wearing MSRS, with the most common body part involved being the foot. Fifty-four respondents (31%) had an injury that improved after adopting minimally shod running; the most common area involved was the knee. One-hundred twenty respondents (69%) were still using MSRS. Of those who stopped using MSRS, the main reason was development of an injury or pain. The most common reason that respondents have not tried minimally shod running is a fear of developing an injury.

CONCLUSION

This survey-based study demonstrated that the use of MSRS is common, largely as the result of a perception that they may reduce injuries or pain. Reductions and occurrences of injury/pain with minimally shod running were reported in approximately equal numbers. The most common site of reported injury/pain reduction was the knee, whereas the most common reported site of injury/pain occurrence was the foot. Fear of developing pain or injury is the most common reason runners are reluctant to try minimally shod running.

Effect of Acute Alterations in Foot Strike Patterns during Running on Sagittal Plane Lower Limb Kinematics and Kinetics

The purpose of this study was to determine the effect of foot strike patterns and converted foot strike patterns on lower limb kinematics and kinetics at the hip, knee, and ankle during a shod condition. Subjects were videotaped with a high speed camera while running a 5km at self-selected pace on a treadmill to determine natural foot strike pattern on day one. Preferred forefoot group (PFFG, n = 10) and preferred rear foot group (PRFG, n = 11) subjects were identified through slow motion video playback (n = 21, age = 22.8±2.2 years, mass = 73.1±14.5 kg, height 1.75 ± 0.10 m). On day two, subjects performed five overground run trials in both their natural and unnatural strike patterns while motion and force data were collected. Data were collected over two days so that foot strike videos could be analyzed for group placement purposes. Several 2 (Foot Strike Pattern -forefoot strike [FFS], rearfoot strike [RFS]) x 2 (Group - PFFG, PRFG) mixed model ANOVAs (p < 0.05) were run on speed, active peak vertical ground reaction force (VGRF), peak early stance and mid stance sagittal ankle moments, sagittal plane hip and knee moments, ankle dorsiflexion ROM, and sagittal plane hip and knee ROM. There were no significant interactions or between group differences for any of the measured variables. Within subject effects demonstrated that the RFS condition had significantly lower (VGRF) (RFS = 2.58 ± .21 BW, FFS = 2.71 ± 0.23 BW), dorsiflexion moment (RFS = -2.6 1± 0.61 Nm·kg(-1), FFS = -3.09 ± 0.32 Nm·kg(-1)), and dorsiflexion range of motion (RFS = 17.63 ± 3.76°, FFS = 22.10 ± 5.08°). There was also a significantly higher peak plantarflexion moment (RFS = 0.23 ± 0.11 Nm·kg(-1), FFS = 0.01 ± 0.01 Nm·kg(-1)), peak knee moment (RFS = 2.61 ± 0.54 Nm·kg(-1), FFS = 2.39 ± 0.61 Nm·kg(-1)), knee ROM (RFS = 31.72 ± 2.79°, FFS = 29.58 ± 2.97°), and hip ROM (RFS = 42.72 ± 4.03°, FFS = 41.38 ± 3.32°) as compared with the FFS condition. This research suggests that acute changes in foot strike patterns during shod running can create alterations in certain lower limb kinematic and kinetic measures that are not dependent on the preferred foot strike pattern of the individual. This research also challenges the contention that the impact transient spike in the vertical ground reaction force curve is only present during a rear foot strike type of running gait. Key pointsFootstrike pattern changes should be individually considered and implemented based on individual histories/abilitiesForefoot strike patterns increase external dorsiflexion momentsRearfoot strike patterns increase external knee flexion momentsRecreational shod runners are able to mimic habitual mechanics of different foot strike patterns.

In-field gait retraining and mobile monitoring to address running biomechanics associated with tibial stress fracture

We sought to determine if an in-field gait retraining program can reduce excessive impact forces and peak hip adduction without adverse changes in knee joint work during running. Thirty healthy at-risk runners who exhibited high-impact forces were randomized to retraining [21.1 (± 1.9) years, 22.1 (± 10.8) km/week] or control groups [21.0 (± 1.3) years, 23.2 (± 8.7) km/week]. Retrainers were cued, via a wireless accelerometer, to increase preferred step rate by 7.5% during eight training sessions performed in-field. Adherence with the prescribed step rate was assessed via mobile monitoring. Three-dimensional gait analysis was performed at baseline, after retraining, and at 1-month post-retraining. Retrainers increased step rate by 8.6% (P < 0.0001), reducing instantaneous vertical load rate (-17.9%, P = 0.003), average vertical load rate (-18.9%, P < 0.0001), peak hip adduction (2.9° ± 4.2 reduction, P = 0.005), eccentric knee joint work per stance phase (-26.9%, P < 0.0001), and per kilometer of running (-21.1%, P < 0.0001). Alterations in gait were maintained at 30 days. In the absence of any feedback, controls maintained their baseline gait parameters. The majority of retrainers were adherent with the prescribed step rate during in-field runs. Thus, in-field gait retraining, cueing a modest increase in step rate, was effective at reducing impact forces, peak hip adduction and eccentric knee joint work.

Gait re-training to alleviate the symptoms of anterior exertional lower leg pain: a case series

BACKGROUND/PURPOSE

Exercise induced lower leg pain (EILP) is a commonly diagnosed overuse injury in recreational runners and in the military with an incidence of 27-33% of all lower leg pain presentations. This condition has proven difficult to treat conservatively and patients commonly undergo surgical decompression of the compartment by fasciotomy. This case series investigates the clinical outcome of patients referred with exertional lower leg pain symptoms of the anterior compartment of the lower leg following a gait re-training intervention program.

CASE DESCRIPTION

10 patients with exercise related running pain in the anterior compartment of the lower leg underwent a gait re-training intervention over a six-week period. Coaching cues were utilized to increase hip flexion, increase cadence, to maintaining an upright torso, and to achieve a midfoot strike pattern. At initial consult and six-week follow up, two-dimensional video analysis was used to measure kinematic data. Patients self reported level of function and painfree running were recorded throughout and at one-year post intervention.

OUTCOMES

Running distance, subjective lower limb function scores and patient's pain improved significantly. The largest mean improvements in function were observed in 'running for 30 minutes or longer' and reported 'sports participation ability' with increases of 57.5% and 50%, respectively. 70% of patients were running painfree at follow-up. Kinematic changes affected at consultation were maintained at follow-up including angle of dorsiflexion, angle of tibia at initial contact, hip flexion angle, and stride length. A mean improvement of the EILP Questionnaire score of 40.3% and 49.2%, at six-week and one-year follow up, respectively.

DISCUSSION

This case series describes a conservative treatment intervention for patients with biomechanical overload syndrome/exertional compartment syndrome of the anterior lower leg. Three of the four coaching cues affected lasting changes in gait kinematics. Significant improvements were shown in painfree running times and function.

LEVEL OF EVIDENCE

4.

Effects of Form-Focused Training on Running Biomechanics: A Pilot Randomized Trial in Untrained Individuals

OBJECTIVE

To investigate the changes in running biomechanics after training in form-focused running using ChiRunning versus not-form focused training and self-directed training in untrained individuals.

DESIGN

Pilot study-randomized controlled trial.

SETTING

Research institution with tertiary care medical center.

PARTICIPANTS

Seventeen subjects (9 men, 8 women) with prehypertension.

METHODS

Twenty-two participants were randomized to 3 study arms but 17 completed the study. The study arms were: (1) group-based Form-Focused running using ChiRunning (enrolled, n = 10; completed, n = 7); (2) group-based conventional running (enrolled, n = 6; completed, n = 4); and (3) self-directed training with educational materials (enrolled, n = 6; completed, n = 6). The training schedule was prescribed for 8 weeks with 4 weeks of follow-up. All subjects completed overground running motion analyses before and after training. ClinicalTrials.gov identifier for this study is NCT0158718.

OUTCOMES

Ankle, knee, hip joint peak moments, and powers; average vertical loading rate (AVLR); impact peak; cadence; stride length; strike index; and stride reach. Paired t tests were used to compare differences within groups over time.

RESULTS

Form-focused group reduced their Stride Reach (P = .047) after the training but not the other groups. Form-focused group showed a close to significant reduction in knee adduction moment (P = .051) and a reduction in the peak ankle eversion moment (P = .027). Self-directed group showed an increase in the running speed (P = .056) and increases in ankle and knee joint powers and moments.

CONCLUSIONS

There are differences in the changes in running biomechanics between individuals trained in running form that emphasizes mid-foot strike, greater cadence, and shorter stride compared with those not trained in the these techniques. These differences may be associated with reduced lower extremity stress in individuals trained in this running form, but more studies are needed to confirm these findings in larger samples.

The effect of running velocity on footstrike angle--a curve-clustering approach

Despite a large number of studies that have considered footstrike pattern, relatively little is known about how runners alter their footstrike pattern with running velocity. The purpose of this study was to determine how footstrike pattern, defined by footstrike angle (FSA), is affected by running velocity in recreational athletes. One hundred and two recreational athletes ran on a treadmill at up to ten set velocities ranging from 2.2-6.1 ms(-1). Footstrike angle (positive rearfoot strike, negative forefoot strike), as well as stride frequency, normalised stride length, ground contact time and duty factor, were obtained from sagittal plane high speed video captured at 240 Hz. A probabilistic curve-clustering method was applied to the FSA data of all participants. The curve-clustering analysis identified three distinct and approximately equally sized groups of behaviour: (1) small/negative FSA throughout; (2) large positive FSA at low velocities (≤ 4 ms(-1)) transitioning to a smaller FSA at higher velocities (≥ 5 ms(-1)); (3) large positive FSA throughout. As expected, stride frequency was higher, while normalised stride length, ground contact time and duty factor were all lower for Cluster 1 compared to Cluster 3 across all velocities; Cluster 2 typically displayed intermediate values. These three clusters of FSA - velocity behaviour, and in particular the two differing trends observed in runners with a large positive FSAs at lower velocities, can provide a novel and relevant means of grouping athletes for further assessment of their running biomechanics.

Association of previous injury and speed with running style and stride-to-stride fluctuations

Running-related injuries remain problematic among recreational runners. We evaluated the association between having sustained a recent running-related injury and speed, and the strike index (a measure of footstrike pattern, SI) and spatiotemporal parameters of running. Forty-four previously injured and 46 previously uninjured runners underwent treadmill running at 80%, 90%, 100%, 110%, and 120% of their preferred running speed. Participants wore a pressure insole device to measure SI, temporal parameters, and stride length (S(length)) and stride frequency (S(frequency)) over 2-min intervals. Coefficient of variation and detrended fluctuation analysis provided information on stride-to-stride variability and correlative patterns. Linear mixed models were used to compare differences between groups and changes with speed. Previously injured runners displayed significantly higher stride-to-stride correlations of SI than controls (P = 0.046). As speed increased, SI, contact time (T(contact)), stride time (T(stride)), and duty factor (DF) decreased (P < 0.001), whereas flight time (T(flight)), S(length), and S(frequency) increased (P < 0.001). Stride-to-stride variability decreased significantly for SI, T(contact), T(flight), and DF (P ≤ 0.005), as did correlative patterns for T(contact), T(stride), DF, S(length), and S(frequency) (P ≤ 0.044). Previous running-related injury was associated with less stride-to-stride randomness of footstrike pattern. Overall, runners became more pronounced rearfoot strikers as running speed increased.

Gait considerations in patients with femoroacetabular impingement

The literature describing the characteristic features of femoroacetabular impingement (FAI) has been on the rise, increasing awareness of this pathology in the young, active population. The physical therapist should consider FAI as a contributing factor to anterior hip pain, impairments, and functional deficits of the lower quarter. The dynamic interplay of anatomical variations, pain, and muscle function and their effects on gait in patients with FAI, however, is poorly understood. Small sample populations and variability in radiological, demographic, and clinical presentations in those with FAI have precluded meaningful insight into gait analysis and FAI, reiterating the need for further research in this domain. The purpose of this clinical commentary is to review the literature that defines normal gait at the hip joint and abnormal gait as a result of FAI and labral pathology or surgery aimed at correcting it. Secondarily, the authors aim to offer clinicians a strategy to progress the post-surgical patient to normal, unassisted gait while reducing the risk for anterior hip pain. Lastly, the authors of this commentary aim to identify specific areas for future research directed at therapeutic interventions in patients with FAI and those who have undergone surgery to correct it.

LEVEL OF EVIDENCE

5.

Rehabilitation of soft tissue injuries of the hip and pelvis

Soft tissue injuries of the hip and pelvis are common among athletes and can result in significant time loss from sports participation. Rehabilitation of athletes with injuries such as adductor strain, iliopsoas syndrome, and gluteal tendinopathy starts with identification of known risk factors for injury and comprehensive evaluation of the entire kinetic chain. Complex anatomy and overlapping pathologies often make it difficult to determine the primary cause of the pain and dysfunction. The purpose of this clinical commentary is to present an impairment-based, stepwise progression in evaluation and treatment of several common soft tissue injuries of the hip and pelvis.

LEVEL OF EVIDENCE

5.

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.

Always on the run

With injury incidence ranging from 26% to 92%, runners are continually seeking the next great cure that will keep them injury free. And the information they receive is often conflicting: land on your heels, land on your toes; stretching makes you faster, stretching makes you slower; wear supportive shoes, do not wear shoes at all. As practitioners, we are often guilty of the same search for a common cause of all running injuries: foot pronation, impact forces, excessive hip motion, and so on. It is a confusing time for runners, as well as for those of us who treat them. By covering a diverse range of running topics, we hope this special running issue of JOSPT improves our understanding of what running is and takes us one step further toward having common answers for those on the run.

Ability of sagittal kinematic variables to estimate ground reaction forces and joint kinetics in running

STUDY DESIGN

Controlled laboratory study, cross-sectional design.

OBJECTIVE

To determine if sagittal kinematic variables can be used to estimate select running kinetics.

BACKGROUND

Excessive loading during running has been implicated in a variety of injuries, yet this information is typically not assessed during a standard clinical examination. Developing a clinically feasible strategy to estimate ground reaction forces and joint kinetics may improve the ability to identify those at an increased risk of injury.

METHODS

Three-dimensional kinematics and ground reaction forces of 45 participants were recorded during treadmill running at self-selected speed. Kinematic variables used to estimate specific kinetic metrics included vertical excursion of the center of mass, foot inclination angle at initial contact, horizontal distance between the center of mass and heel at initial contact, knee flexion angle at initial contact, and peak knee flexion angle during stance. Linear mixed-effects models were fitted to explore the association between the kinetic and kinematic measures, including step rate and sex, with final models created using backward variable selection.

RESULTS

Models were developed to estimate peak knee extensor moment (R(2) = 0.43), energy absorbed at the knee during loading response (R(2) = 0.58), peak patellofemoral joint reaction force (R(2) = 0.55), peak vertical ground reaction force (R(2) = 0.48), braking impulse (R(2) = 0.50), and average vertical loading rate (R(2) = 0.04).

CONCLUSION

Our findings suggest that insights into important running kinetics can be obtained from a subset of sagittal plane kinematics common to a clinical running analysis. Of note, the limb posture at initial contact influenced subsequent loading patterns in stance.

Management and prevention of bone stress injuries in long-distance runners

SYNOPSIS

Bone stress injury (BSI) represents the inability of bone to withstand repetitive loading, which results in structural fatigue and localized bone pain and tenderness. A BSI occurs along a pathology continuum that begins with a stress reaction, which can progress to a stress fracture and, ultimately, a complete bone fracture. Bone stress injuries are a source of concern in long-distance runners, not only because of their frequency and the morbidity they cause but also because of their tendency to recur. While most BSIs readily heal following a period of modified loading and a progressive return to running activities, the high recurrence rate of BSIs signals a need to address their underlying causative factors. A BSI results from disruption of the homeostasis between microdamage formation and its removal. Microdamage accumulation and subsequent risk for development of a BSI are related both to the load applied to a bone and to the ability of the bone to resist load. The former is more amenable to intervention and may be modified by interventions aimed at training-program design, reducing impact-related forces (eg, instructing an athlete to run "softer" or with a higher stride rate), and increasing the strength and/or endurance of local musculature (eg, strengthening the calf for tibial BSIs and the foot intrinsics for BSIs of the metatarsals). Similarly, malalignments and abnormal movement patterns should be explored and addressed. The current commentary discusses management and prevention of BSIs in runners. In doing so, information is provided on the pathophysiology, epidemiology, risk factors, clinical diagnosis, and classification of BSIs.

LEVEL OF EVIDENCE

Therapy, level 5.

Hip muscle loads during running at various step rates

STUDY DESIGN

Controlled laboratory study, cross-sectional. Objectives To characterize hip muscle forces and powers during running, and to determine how these quantities change when altering step rate for a given running speed.

BACKGROUND

Hip musculature has been implicated in a variety of running-related injuries and, as such, is often the target of rehabilitation interventions, including resistance exercises and gait retraining. The differential contributions of the hip muscles to the task of running are not well understood, and may be important for recognizing the biomechanical mechanisms of running-related injuries and refining current treatment and prevention strategies.

METHODS

Thirty healthy participants ran at their preferred speed at 3 different step rates: 90%, 100%, and 110% of their preferred step rate. Whole-body kinematics and ground reaction forces were recorded. A 3-D musculoskeletal model was used to estimate muscle forces needed to produce the measured joint accelerations. Forces and powers of each muscle were compared across step-rate conditions.

RESULTS

Peak force produced by the gluteus medius during running was substantially greater than that of any other hip muscle, with the majority of muscles displaying a period of negative work immediately preceding positive work. The higher running step rate led to an increase in hip flexor, hamstring, and hip extensor loading during swing, but, conversely, substantially diminished peak force and work during loading response for several hip muscles, including the gluteal muscles and piriformis.

CONCLUSION

Increasing running step rate for a given running speed heightened hamstring and gluteal muscle loading in late swing, while decreasing stance-phase loading in the gluteal muscles and piriformis. These results may enable clinicians to support and refine current treatment strategies, including exercise prescription and gait retraining for running-related injuries.

Prolonged cycling alters stride time variability and kinematics of a post-cycle transition run in triathletes

Previous studies have employed relatively short cycling protocols to investigate the effect of cycling on muscle activation and kinematics in running. The aim of this study was to investigate the effect of 3h of cycling on stride time variability (STV), stride length, tibialis anterior (TA) activation, and lower limb range of motion (ROM) in a transition run. Eight triathletes completed a run-cycle-run protocol. Data were collected from a pre-cycle run and a transition run after 3h of cycling. STV, stride length and ROM were assessed using three-dimensional motion analysis, and TA activation was recorded using surface electromyography. Results showed that compared with the pre-cycle run triathletes exhibited increased STV (Cohen's d=0.95) and shorter strides (d=0.15) in the transition run (p<0.05). TA activation and ROM did not change. After 10min of transition running, ankle and hip ROM significantly increased (d=0.40 and 0.41 respectively) compared to the beginning of the transition run (p<0.05) but no other changes were observed. The results suggest that locomotor control and kinematics in a transition run are affected by prolonged cycling and stride time variability is potentially a novel method of evaluating the immediate effect of prolonged cycling on the locomotor control of running.

The biomechanical differences between barefoot and shod distance running: a systematic review and preliminary meta-analysis

BACKGROUND

Distance running continues to experience increased participation in the Western world, although it is associated with high injury rates. Barefoot running has been increasingly proposed as a means to prevent overuse injury due to various biomechanical differences, including reduced joint loading rates and altered kinematics and muscle activity patterns compared to shod running.

OBJECTIVE

The aim of this review was to systematically evaluate biomechanical differences between running barefoot and shod, including the quality of available evidence, in order to provide guidance on the phenomenon of barefoot running to the running and sports medicine communities.

DATA SOURCES

A comprehensive search of MEDLINE, Web of Knowledge and EMBASE from inception to January 2013 was performed.

STUDY SELECTION

Trials evaluating injury-free recreational or competitive adults who participate in long-distance running (≥5 km), where a comparison of barefoot and shod running lower-limb kinetics, kinematics and/or electromyography were included. Studies examining sprinting and studies of single-subject design were excluded.

STUDY APPRAISAL AND SYNTHESIS METHODS

Following initial searching, two reviewers identified a shortlist of relevant studies based on title and abstract, with the full text of these studies being tested against the inclusion criteria. References of included studies were examined and citation tracking was performed in Web of Knowledge. Two independent reviewers evaluated the methodological quality of each included study using a modified version of the Downs and Black quality index. Results of the quality assessment were used to identify high- and low-quality studies, data pooling was completed where possible and levels of evidence were determined based on the van Tulder criteria.

RESULTS

Eighteen studies were identified, all of low methodological quality. Effect size (ES) calculation was possible for 12 studies. Pooled results indicate moderate evidence that barefoot running is associated with reduced peak ground reaction force (GRF), increased foot and ankle plantarflexion and increased knee flexion at ground contact compared with running in a neutral shoe. Limited evidence indicates barefoot running is associated with reduced impact GRF, reduced peak knee flexion and varus joint moments, and a higher stride frequency compared to a neutral shoe. Very limited to limited evidence also indicates power absorption at the knee is decreased while being increased at the ankle whilst barefoot running. Additionally, the effects of barefoot running on loading rate appear dependent on strike pattern adopted, with a forefoot strike pattern found to reduce loading rate, whilst a rearfoot strike pattern increases loading rate when running barefoot compared to shod.

LIMITATIONS

Key methodological weaknesses that must be addressed in future research were identified. Of particular note were absence of investigator blinding, infrequent intervention randomisation, small sample sizes and lack of evaluation following habituation. Two studies could not be retrieved because of publication in a non-English-language journal. Of particular note is that the validity of the body of work is compromised by the lack of evaluation after habituation, or re-training, of previously shod rearfoot-striking runners to barefoot forefoot-striking running styles.

CONCLUSIONS

There has been a great deal of publicity for barefoot running, and many claims made about its effects and risks. Despite a large amount of biomechanical data available for meta-analysis, clear guidance for clinical practice is limited because of the low methodological quality of the associated studies. Preliminary biomechanical differences identified suggest barefoot running may be associated with positive biomechanical changes in regards to injury prevention, although this may be dependent on strike pattern adopted. Further research employing more robust methodology, which addresses weaknesses highlighted in this review, is needed to confirm current preliminary evidence. Additionally, prospective research would have higher validity were the biomechanical effects of habituating to barefoot running fully examined alongside an evaluation of prevention of repetitive use injury.

Is there evidence to support a forefoot strike pattern in barefoot runners? A review

Context:

Barefoot running is a trend among running enthusiasts that is the subject of much controversy. At this time, benefits appear to be more speculative and anecdotal than evidence based. Additionally, the risk of injuries is not well established.

Evidence acquisition:

A PubMed search was undertaken for articles published in English from 1980 to 2011. Additional references were accrued from reference lists of research articles.

Results:

While minimal data exist that definitively support barefoot running, there are data lending support to the argument that runners should use a forefoot strike pattern in lieu of a heel strike pattern to reduce ground reaction forces, ground contact time, and step length.

Conclusions:

Whether there is a positive or negative effect on injury has yet to be determined. Unquestionably, more research is needed before definitive conclusions can be drawn.

Influence of stride frequency and length on running mechanics: a systematic review

Context:

A high number of recreational runners sustain a running-related injury each year. To reduce injury risk, alterations in running form have been suggested. One simple strategy for running stride frequency or length has been commonly advocated.

Objective:

To characterize how running mechanics change when stride frequency and length are manipulated.

Data Sources:

In January 2012, a comprehensive search of PubMed, CINAHL Plus, SPORTDiscus, PEDro, and Cochrane was performed independently by 2 reviewers. A second search of the databases was repeated in June 2012 to ensure that no additional studies met the criteria after the initial search.

Study Selection:

Inclusion criteria for studies were an independent variable including manipulation of stride frequency or length at a constant speed with outcome measures of running kinematics or kinetics.

Study Design:

Systematic review.

Level of Evidence:

Level 3.

Data Extraction:

Two reviewers independently appraised each article using a modified version of the Quality Index, designed for assessing bias of nonrandomized studies.

Results:

Ten studies met the criteria for this review. There was consistent evidence that increased stride rate resulted in decreased center of mass vertical excursion, ground reaction force, shock attenuation, and energy absorbed at the hip, knee, and ankle joints. All but 1 study had a limited number of participants, with several methodological differences existing among studies (eg, overground and treadmill running, duration of test conditions). Although speed was held constant during testing, it was individually self-selected or fixed. Most studies used only male participants.

Conclusion:

Despite procedural differences among studies, an increased stride rate (reduced stride length) appears to reduce the magnitude of several key biomechanical factors associated with running injuries.

Treatment of distal iliotibial band syndrome in a long distance runner with gait re-training emphasizing step rate manipulation

BACKGROUND & PURPOSE

Iliotibial band syndrome (ITBS) is a common injury associated with long distance running. Researchers have previously described biomechanical factors associated with ITBS. The purpose of this case report is to present the treatment outcomes in a runner with distal ITBS utilizing running gait re-training to increase step rate above the runner's preferred or self-chosen step rate.

CASE DESCRIPTION

The subject was a 36 year old female runner with a diagnosis of left knee ITBS, whose pain prevented her from running greater than three miles for three months. Treadmill video analysis of running form was utilized to determine that the subject had an excessive stride length, strong heel strike, decreased knee flexion angle at initial foot contact, and excessive vertical displacement. Cadence was 168 steps/minute at a preferred running pace of 6.5 mph. Treatment emphasized gait re-training to increase cadence above preferred. Treatment also included iliotibial band flexibility and multi-plane eccentric lower extremity strengthening.

OUTCOMES

The subject reported running pain free within 6 weeks of the intervention with a maximum running distance of 7 miles and 10-15 miles/week progressing to half marathon distance and 20-25 miles/week at 4 month follow up. Step rate increased 5% to 176 steps/minute and was maintained at both the 6 week and 4 month follow up. 5K run pace improved from 8:45 to 8:20 minutes/Km. LEFS score improved from 71/80 to 80/80 at 4 month follow up.

DISCUSSION

This case demonstrated that a 5% increased step rate above preferred along with a home exercise program for hip strengthening and iliotibial band stretching, improved running mechanics and reduced knee pain in a distance runner.

LEVEL OF EVIDENCE

4-single case report.

Effects of step length on patellofemoral joint stress in female runners with and without patellofemoral pain

BACKGROUND

Patellofemoral pain is common among runners and is frequently attributed to increased patellofemoral joint stress. The purpose of our study was to examine the effects of changing step length during running on patellofemoral joint stress per step and stress per mile in females with and without patellofemoral pain.

METHODS

Ten female runners with patellofemoral pain and 13 healthy female runners performed running trials at 3.7m/s in three conditions: preferred step length, at least +10% step length, and at least -10% step length. Knee flexion angles and internal knee extension moments served as inputs for a biomechanical model to estimate patellofemoral joint stress per step. We also estimated total patellofemoral joint stress per mile based on the number of steps necessary to run a mile during each condition.

FINDINGS

Patellofemoral joint stress per step increased 31% in the long step length condition (P<.001) and decreased 22.2% in the short step length condition (P<.001). Despite the inverse relationship between step length and number of steps required to run a mile, patellofemoral joint stress per mile increased 14% in the long step length condition (P<.001) and decreased 7.5% in the short step length condition (P<.001).

INTERPRETATION

These results suggest a direct relationship between step length and patellofemoral joint loads. Total stress per mile experienced at the patellofemoral joint decreased with a short step length despite the greater number of steps necessary to cover this distance. These findings may have relevance with respect to both prevention and treatment of patellofemoral joint pain.

Low-frequency accelerations over-estimate impact-related shock during walking

During gait, a failure to acknowledge the low-frequency component of a segmental acceleration signal will result in an overestimation of impact-related shock and may lead to inappropriately drawn conclusions. The present study was undertaken to investigate the significance of this low-frequency component in two distinctly different modalities of gait: barefoot (BF) and shod (SHOD) walking. Twenty-seven participants performed five walking trials at self-selected speed in each condition. Peak positive accelerations (PPA) at the shank and spine were first derived from the time-domain signal. The raw acceleration signals were then resolved in the frequency-domain and the active (low-frequency) and impact-related components of the power spectrum density (PSD) were quantified. PPA was significantly higher at the shank (P<0.0001) and spine (P=0.0007) in the BF condition. In contrast, no significant differences were apparent between conditions for shank (P=0.979) or spine (P=0.178) impact-related PSD when the low-frequency component was considered. This disparity between approaches was due to a significantly higher active PSD in both signals in the BF condition (P<0.0001; P=0.008, respectively), due to kinematic differences between conditions (P<0.05). These results indicate that the amplitude of the low-frequency component of an acceleration signal during gait is dependent on knee and ankle joint coordination behaviour, and highlight that impact-related shock is more accurately quantified in the frequency-domain following subtraction of this component.

Barefoot running: an evaluation of current hypothesis, future research and clinical applications

Barefoot running has become a popular research topic, driven by the increasing prescription of barefoot running as a means of reducing injury risk. Proponents of barefoot running cite evolutionary theories that long-distance running ability was crucial for human survival, and proof of the benefits of natural running. Subsequently, runners have been advised to run barefoot as a treatment mode for injuries, strength and conditioning. The body of literature examining the mechanical, structural, clinical and performance implications of barefoot running is still in its infancy. Recent research has found significant differences associated with barefoot running relative to shod running, and these differences have been associated with factors that are thought to contribute to injury and performance. Crucially, long-term prospective studies have yet to be conducted and the link between barefoot running and injury or performance remains tenuous and speculative. The injury prevention potential of barefoot running is further complicated by the complexity of injury aetiology, with no single factor having been identified as causative for the most common running injuries. The aim of the present review was to critically evaluate the theory and evidence for barefoot running, drawing on both collected evidence as well as literature that have been used to argue in favour of barefoot running. We describe the factors driving the prescription of barefoot running, examine which of these factors may have merit, what the collected evidence suggests about the suitability of barefoot running for its purported uses and describe the necessary future research to confirm or refute the barefoot running hypotheses.

A comparison of negative joint work and vertical ground reaction force loading rates in Chi runners and rearfoot-striking runners

STUDY DESIGN

Observational.

OBJECTIVES

To compare lower extremity negative joint work and vertical ground reaction force loading rates in rearfoot-striking (RS) and Chi runners.

BACKGROUND

Alternative running styles such as Chi running have become a popular alternative to RS running. Proponents assert that this running style reduces knee joint loading and ground reaction force loading rates.

METHODS

Twenty-two RS and 12 Chi runners ran for 5 minutes at a self-selected speed on an instrumented treadmill. A 3-D motion analysis system was used to obtain kinematic data. Average vertical ground reaction force loading rate and negative work of the ankle dorsiflexors, ankle plantar flexors, and knee extensors were computed during the stance phase. Groups were compared using a 1-way analysis of covariance for each variable, with running speed and age as covariates.

RESULTS

On average, RS runners demonstrated greater knee extensor negative work (RS, -0.332 J/body height × body weight [BH·BW]; Chi, -0.144 J/BH·BW; P<.001), whereas Chi runners demonstrated more ankle plantar flexor negative work (Chi, -0.467 J/BH·BW; RS, -0.315 J/BH·BW; P<.001). RS runners demonstrated greater average vertical ground reaction force loading rates than Chi runners (RS, 68.6 BW/s; Chi, 43.1 BW/s; P<.001).

CONCLUSION

Chi running may reduce vertical loading rates and knee extensor work, but may increase work of the ankle plantar flexors.

Prevention of overuse sports injuries in the young athlete

The purpose of this article is to review the current theories regarding prevalence, mechanism, and prevention strategies for overuse injuries in a young athletic population. This information provides valuable insight into the state of the current evidence regarding overuse injuries in young athletes as well as the potential future directions in the development of overuse injury prevention interventions.

Effect of adaptive paced cardiolocomotor synchronization during running: a preliminary study

Cardiolocomotor synchronization (CLS) has been well established for individuals engaged in rhythmic activity, such as walking, running, or cycling. When frequency of the activity is at or near the heart rate, entrainment occurs. CLS has been shown in many cases to improve the efficiency of locomotor activity, improving stroke volume, reducing blood pressure variability, and lowering the oxygen uptake (VO2). Instead of a 1:1 frequency ratio of activity to heart rate, an investigation was performed to determine if different harmonic coupling at other simple integer ratios (e.g. 1:2, 2:3, 3:2) could achieve any performance benefits. CLS was ensured by pacing the stride rate according to the measured heartbeat (i.e., adaptive paced CLS, or forced CLS). An algorithm was designed that determined the simplest ratio (lowest denominator) that, when multiplied by the heart rate will fall within an individualized, predetermined comfortable pacing range for the user. The algorithm was implemented on an iPhone 4, which generated a 'tick-tock' sound through the iPhone's headphones. A sham-controlled crossover study was performed with 15 volunteers of various fitness levels. Subjects ran a 3 mile (4.83 km) simulated training run at their normal pace on two consecutive days (randomized one adaptive pacing, one sham). Adaptive pacing resulted in faster runs run times, with subjects running an average of 26:03 ± 3:23 for adaptive pacing and 26:38 ± 3:31 for sham (F = 5.46, p < 0.05). The increase in heart rate from the start of the race as estimated by an exponential time constant was significantly longer during adaptive pacing, τ = 0.99 ± 0.30, compared to sham, τ = 1.53 ± 0.34 (t = -6.62, p < 0.01). Eighty-seven percent of runners found it easy to adjust their stride length to match the pacing signal with seventy-nine percent reporting that pacing helped their performance. These results suggest that adaptive paced CLS may have a beneficial effect on running performance and may be useful as a training aid. Key PointsSham-controlled crossover study using 15 experienced runners running 3 miles (4.83 km).Adaptive CLS pacing resulted in statistically significant 35 second average decrease in run-time (p < 0.05).Increase in heart rate during the run was significantly slower during adaptive pacing (p < 0.01).

Changes in timing of muscle contractions and running economy with altered stride pattern during running

Large alterations to the preferred running stride decrease running economy, and shorter strides increase leg muscle activity. However, the effect of altered strides on the timing of leg muscle activation is not known. The aim of this study was to evaluate the impact of moderate alterations to the running stride on running economy and the timing of biceps femoris (BF), vastus lateralis (VL) and gastrocnemius (GAST) muscle contractions. The preferred stride pattern for eleven trained male runners was measured prior to a separate visit where participants ran for bouts of 5 min whilst synchronising foot contacts to a metronome signal which was tuned to (1) the preferred stride, and (2) frequencies which related to ± 8% and ± 4% of the preferred stride length. Running economy was measured at each stride pattern along with electromyography and three-dimensional kinematics to estimate onset and offset of muscle contractions for each muscle. Running economy was greatest at the preferred stride length. However, a quadratic fit to the data was optimised at a stride which was 2.9% shorter than preferred. Onset and offset of BF and VL muscle contractions occurred earlier with shorter than preferred strides. We detected no changes to the timing of muscle contractions with longer than preferred strides and no changes to GAST muscle contractions. The results suggest that runners optimise running economy with a stride length that is close to, but shorter than, the preferred stride, and that timing of BF and VL muscle contractions change with shorter than preferred strides.

Adolescent runners: the effect of training shoes on running kinematics

BACKGROUND

The modern running shoe typically features a large cushioned heel intended to dissipate the energy at heel strike to the knees and hips. The purpose of this study was to evaluate the effect that shoes have upon the running biomechanics among competitive adolescent runners. We wish to answer the question of whether running style is altered in these athletes because of footwear.

METHODS

Twelve competitive adolescent athletes were recruited from local track teams. Each ran on a treadmill in large heel trainers, track flats, and barefoot. Four different speeds were used to test each athlete. The biomechanics were assessed with a motion capture system. Stride length, heel height during posterior swing phase, and foot/ground contact were recorded.

RESULTS

Shoe type markedly altered the running biomechanics. The foot/ground contact point showed differences in terms of footwear (P<0.0001) and speed (P=0.000215). When wearing trainers, the athletes landed on their heels 69.79% of the time at all speeds (P<0.001). The heel was the first point of contact <35% of the time in the flat condition and <30% in the barefoot condition.

CONCLUSIONS

Running biomechanics are significantly altered by shoe type in competitive adolescents. Heavily heeled cushioned trainers promote a heel strike pattern, whereas track flats and barefoot promote a forefoot or midfoot strike pattern. Training in heavily cushioned trainers by the competitive runner has not been clearly shown to be detrimental to performance, but it does change the gait pattern. It is not known whether the altered biomechanics of the heavily heeled cushioned trainer may be detrimental to the adolescent runner who is still developing a running style.

Foot-strike pattern and performance in a marathon

PURPOSE

To determine prevalence of heel strike in a midsize city marathon, if there is an association between foot-strike classification and race performance, and if there is an association between foot-strike classification and gender.

METHODS

Foot-strike classification (forefoot, midfoot, heel, or split strike), gender, and rank (position in race) were recorded at the 8.1-km mark for 2112 runners at the 2011 Milwaukee Lakefront Marathon.

RESULTS

1991 runners were classified by foot-strike pattern, revealing a heel-strike prevalence of 93.67% (n = 1865). A significant difference between foot-strike classification and performance was found using a Kruskal-Wallis test (P < .0001), with more elite performers being less likely to heel strike. No significant difference between foot-strike classification and gender was found using a Fisher exact test. In addition, subgroup analysis of the 126 non-heel strikers found no significant difference between shoe wear and performance using a Kruskal-Wallis test.

CONCLUSIONS

The high prevalence of heel striking observed in this study reflects the foot-strike pattern of most mid-distance to long-distance runners and, more important, may predict their injury profile based on the biomechanics of a heel-strike running pattern. This knowledge can help clinicians appropriately diagnose, manage, and train modifications of injured runners.