Effects of step rate manipulation on joint mechanics during running

Real-time feedback by wearables in running: Current approaches, challenges and suggestions for improvements

Injuries and lack of motivation are common reasons for discontinuation of running. Real-time feedback from wearables can reduce discontinuation by reducing injury risk and improving performance and motivation. There are however several limitations and challenges with current real-time feedback approaches. We discuss these limitations and challenges and provide a framework to optimise real-time feedback for reducing injury risk and improving performance and motivation. We first discuss the reasons why individuals run and propose that feedback targeted to these reasons can improve motivation and compliance. Secondly, we review the association of running technique and running workload with injuries and performance and we elaborate how real-time feedback on running technique and workload can be applied to reduce injury risk and improve performance and motivation. We also review different feedback modalities and motor learning feedback strategies and their application to real-time feedback. Briefly, the most effective feedback modality and frequency differ between variables and individuals, but a combination of modalities and mixture of real-time and delayed feedback is most effective. Moreover, feedback promoting perceived competence, autonomy and an external focus can improve motivation, learning and performance. Although the focus is on wearables, the challenges and practical applications are also relevant for laboratory-based gait retraining.

Association Between Gait Kinetics and Symptomatic Progression in Persons With Patellofemoral With/Without Concurrent Tibiofemoral Osteoarthritis

To identify the biomechanical risk factors associated with symptomatic progression at 1-year follow-up in persons with patellofemoral joint (PFJ) osteoarthritis (OA). Patients' self-reported Knee Injury and Osteoarthritis Outcome Score questionnaires, magnetic resonance (MR) imaging, and three-dimensional gait analysis were obtained in 53 subjects with PFJ OA at baseline and after 1 year. Joint OA was diagnosed on knee MR images if cartilage lesions existed. Progression was defined by worsening of patients' self-reported symptoms from baseline to 1 year exceeding the minimal detectable change score. Analysis of covariance was used to compare peak knee flexion moment, knee flexion moment impulse, and vertical ground reaction force loading rate between progressors and non-progressors. Seven (13.2%) subjects exhibited progression in self-reported symptoms at 1-year follow-up. When comparing to non-progressors, significantly higher peak knee flexion moment during first half of stance (p = 0.017) and higher moment impulse during the both halves of stance were observed among progressors (p = 0.020-0.040). Persons with symptomatic PFJ OA progression with or without concurrent tibiofemoral OA exhibited abnormal joint loading mechanics when compared with individuals who did not progress. Further work is needed to determine if modification to these loading variables results in a change in the symptomatic progression in these individuals. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2593-2600, 2019.

THE EFFECT OF AN ANTI-GRAVITY TREADMILL ON RUNNING CADENCE

BACKGROUND

Running cadence, or step rate, is often measured in running gait analysis and manipulated in gait retraining. A lower body positive pressure treadmill, or anti-gravity treadmill, allows users to walk/run in a reduced gravity environment.

PURPOSE

The primary purpose of this study was to determine how natural running cadence is affected by running on an anti-gravity treadmill compared to a standard treadmill in a healthy, active population. The secondary purpose was to determine if natural and increased cadence is affected by amount of body weight support.

STUDY DESIGN

Cross-sectional study (convenience sample).

METHODS

Thirty participants were recruited to run on an anti-gravity treadmill (AlterG Anti-Gravity Treadmill^TM M320) at their pre-determined, self-selected, comfortable treadmill speed. Cadence was recorded at nine randomized bodyweight conditions, ranging from 100% of body weight to 20% of body weight, in 10% increments. An additional nine participants were recruited to try to replicate their natural, standard treadmill cadence, as well as increase it by 5% and 10%, while on an anti-gravity treadmill with the same randomized body weight conditions.

RESULTS

Thirty participants, 19 females and 11 males, mean age 27.3 years (range, 22-45), completed Part 1 of the study protocol, while nine additional participants (2 females and 7 males) with a mean age of 29.6 years old (range, 25-40 years) completed Part 2 of the protocol. There was a significant effect of natural running cadence on the anti-gravity treadmill at reduced body weight percentages (p<.01). Post-hoc t-tests revealed that every 10% bodyweight interval was significantly lower than the previous 10% interval (p<.01) on the anti-gravity treadmill, with cadence decreases ranging from 1.5%-3.5% between intervals. Seven of the nine (77.8%) participants in Part 2 were able to replicate and increase their cadence at all body weight levels on the anti-gravity treadmill.

CONCLUSIONS

Decreasing bodyweight level on an anti-gravity treadmill yields a significant and linear decrease in running cadence when performed at a self-selected, moderate intensity pace. Further, the vast majority of participants were able to successfully replicate and increase cadence at all levels of bodyweight percentage.

Acute changes in sagittal plane kinematics while wearing a novel belt device during treadmill running

Somatosensory feedback is used in walking retraining; however, its utility in running is less feasible due to the greater associated speeds. The purpose of this study was to examine the acute effects of wearing a novel running belt device on sagittal plane running kinematics. Ten healthy runners ran on a treadmill with and without the use of a running belt device within a repeated measures study design. Temporal-spatial characteristics and sagittal plane knee and ankle kinematics were recorded with three-dimensional motion analysis. Wilcoxon Signed-Rank Tests revealed significant decreases in centre of mass vertical displacement (z = -2.083, p = 0.003), tibial inclination at initial contact (z = -2.803, p = 0.003), and stance phase knee joint excursion (z = -2.701, p = 0.003), and greater knee flexion at initial contact (z = -2.803, p = 0.003) when the belt was donned. No differences were observed in step rate (z = -0.351, p = 0.363), foot inclination angle at initial contact (z = -2.090, p = 0.018), or peak knee flexion during stance (z = -1.172, p = 0.121). Findings suggest that donning a running belt can minimise specific high-risk biomechanical characteristics in runners with particular kinematic profiles.

How Do Spatiotemporal Parameters and Lower-Body Stiffness Change with Increased Running Velocity? A Comparison Between Novice and Elite Level Runners

This study aimed to examine the effect of running velocity on spatiotemporal parameters and lower-body stiffness of endurance runners, and the influence of the performance level on those adaptations. Twenty-two male runners (novice [NR], n = 12, and elite runners [ER], n = 10) performed an incremental running test with a total of 5 different running velocities (10, 12, 14, 16, 18 km/h). Each condition lasted 1 min (30 s acclimatization period, and 30 s recording period). Spatiotemporal parameters were measured using the OptoGait system. Vertical (Kvert) and leg (Kleg) stiffness were calculated according to the sine-wave method. A repeated measures ANOVA (2 x 5, group x velocities) revealed significant adaptations (p < 0.05) to increased velocity in all spatiotemporal parameters and Kvert in both NR and ER. ER showed a greater flight time (FT) and step angle (at 18 km/h) (p < 0.05), longer step length (SL) and lower step frequency (SF) (p < 0.05), whereas no between-group differences were found in contact time (CT) nor in the sub-phases during CT at any speed (p ≥ 0.05). ER also showed lower Kvert values at every running velocity (p < 0.05), and no differences in Kleg (p ≥ 0.05). In conclusion, lower SF and Kvert and, thereby, longer FT and SL, seem to be the main spatiotemporal characteristics of high-level runners compared to their low-level counterparts.

Association Between Temporal Spatial Parameters and Overuse Injury History in Runners: A Systematic Review and Meta-analysis

BACKGROUND

Temporal spatial parameters during running are measurable outside of clinical and laboratory environments using wearable technology. Data from wearable technology may be useful for injury prevention, however the association of temporal spatial parameters with overuse injury in runners remains unclear.

OBJECTIVE

To identify the association between overuse injury and temporal spatial parameters during running.

DATA SOURCES

Electronic databases were searched using keywords related to temporal spatial parameters, running, and overuse injury, and authors' personal article collections through hand search.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Articles included in this systematic review contained original data, and analytically compared at least one temporal spatial parameter (e.g. cadence) between uninjured and retrospectively or prospectively injured groups of runners. Articles were excluded from this review if they did not meet these criteria or measured temporal spatial parameters via survey.

STUDY APPRAISAL AND SYNTHESIS METHOD

The internal validity of each article was assessed using the National Institutes of Health Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. Meta-analyses were conducted for temporal spatial parameters if data existed from at least three separate cohorts of the same prospective or retrospective design. Data were pooled and analyzed using an inverse variance fixed-effect model.

RESULTS

Thirteen articles which tested a total of 24 temporal spatial parameters during running were included in the review. Meta-analyses were conducted on four temporal spatial parameters using data from eleven retrospective studies. Healthy runners and those with a history of overuse injury had a similar average stride time (mean difference: 0.00 s, 95% CI - 0.01 to 0.01 s), contact time (mean difference: 0.00 s, 95% CI 0.00 to 0.01 s), cadence (mean difference: 0.3 steps per minute (spm), 95% CI - 1.8 to 2.5 spm), and stride length (mean difference 0.00 m, 95% CI - 0.05 to 0.05 m) during running.

LIMITATIONS

Data pooled for meta-analyses were limited to retrospective design studies. Studies included in the systematic review had low methodological consistency.

CONCLUSION

Based on pooled results from multiple studies, stride time, contact time, cadence, and stride length averages are not distinguishable between runners either with or without a history of overuse injury. More prospective studies are required to determine the association of temporal spatial parameters with overuse injury development in runners.

SYSTEMATIC REVIEW REGISTRATION REGISTRY AND NUMBER

CRD42018112290.

Association Between Running Shoe Characteristics and Lower Extremity Injuries in United States Military Academy Cadets

BACKGROUND

Running-related overuse injuries are very common among recreational runners, with the reported annual injury rates ranging from 39% to 85%. Relatively few large prospective cohort studies have been conducted to investigate injury risk associated with different running shoe characteristics, and the results of the existing studies are often contradictory.

PURPOSE/HYPOTHESIS

The purpose was to investigate the relationship between running shoe characteristics and lower extremity musculoskeletal injury. It was hypothesized that the risk of injury would be increased in individuals wearing shoes with minimal torsional stiffness and heel height compared with those wearing shoes with greater levels of torsional stiffness and heel height.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

The study included 1025 incoming cadets. Shoe torsional stiffness and heel height were calculated and recorded. Demographic data were recorded and analyzed as potential covariates. Lower extremity injuries sustained over 9 weeks during cadet basic training were documented by use of the Armed Forces Health Longitudinal Technology Application and the Cadet Illness and Injury Tracking System. Kaplan-Meier survival curves were estimated, with time to incident lower extremity injury as the primary outcome by level of the independent predictor variables. Risk factors or potential covariates were carried forward into multivariable Cox proportional hazards regression models. Absolute and relative risk reduction and numbers needed to treat were calculated.

RESULTS

Approximately 18.1% of participants incurred a lower extremity injury. Cadets wearing shoes with moderate lateral torsional stiffness were 49% less likely to incur any type of lower extremity injury and 52% less likely to incur an overuse lower extremity injury than cadets wearing shoes with minimal lateral torsional stiffness, both of which were statistically significant observations. Injury risk was similar among cadets wearing shoes with minimal and extreme lateral torsional stiffness.

CONCLUSION

Shoes with mild to moderate lateral torsional stiffness may be appropriate in reducing risk of lower extremity injury in cadets. Shoes with minimal lateral torsional stiffness should be discouraged in this population.

Reducing vertical ground reaction forces: The relative importance of three gait retraining cues

BACKGROUND

Previous studies in our department demonstrated that gait retraining as part of a conservative treatment program for service members with exercise-related leg pain can lead to persistent changes in vertical ground reaction forces while running in shoes and boots. It is not known which gait retraining cue has the largest effect and whether a combination of cues is advantageous.

METHODS

During a single gait retraining session, 12 male heel striking patients were given three cues in isolation: Cue 1. Change to a ball-of-foot strike; Cue 2. Increase cadence to 180 steps per minute; Cue 3. Stand up taller; and finally, all three cues combined. Runs were performed on an instrumented treadmill at 10 km/h, 1% incline and in running shoes. The three cues were randomly introduced. Measurements, taken during 30-second episodes, were stride length, cadence, and six force variables: maximum force (N) and maximum pressure (N/cm²) on the heel, mid-foot and fore-foot.

FINDINGS

Each cue, i.e., each change in running technique, caused a different pattern of changes among the six force variables, mostly reductions. In isolation, cue 1 produced the largest reduction of force and pressure on the heel, resulting percentages 45.8 and 67.2 respectively (p = 0.00, p = 0.00). Overall, the combination of cues 1 + 2 + 3 ranked first in reducing forces for four of the six force variables.

INTERPRETATION

Three commonly used gait retraining cues, when applied in isolation, all resulted in a reduction of most vertical ground reaction forces. The combination of the three cues is advantageous.

Evidence based treatment options for common knee injuries in runners

The purpose of this paper is to review the current literature regarding conservative treatment options for the three most common knee injuries in runners including patellofemoral pain syndrome (PFPS), iliotibial band friction syndrome (ITBFS), and patellar tendinopathy (PT). Each diagnosis is discussed using current research to describe the pathophysiology, evaluation process, and evidence based effective treatment strategies including therapeutic exercise, manual therapy, neuromuscular re-education, and modalities. The result is a comprehensive overview of each diagnosis and a research-based approach to effectively evaluate and treat each condition for best outcomes.

Immediate effect of visual, auditory and combined feedback on foot strike pattern

BACKGROUND

A growing body of literature supports the promising effect of real-time feedback to re-train runners. However, no studies have comprehensively assessed the effects of foots trike and cadence modification using different forms of real-time feedback provided via wearable devices.

RESEARCH QUESTION

The purpose of the present study was to determine if a change could be made in foot strike pattern and plantar loads using real-time visual, auditory and combined feedback provided using wearable devices.

METHODS

Visual, auditory and combined feedback were provided using wearable devices as fifteen recreational runners ran on a treadmill at self-selected speed and increased cadence. Plantar loads and location of initial contact were measured with a flexible insole system. Repeated measures ANOVAs with Bonferroni adjusted pair-wise comparisons were used to assess statistical significance.

RESULTS AND SIGNIFICANCE

A significant effect of condition was noted on location of center of pressure (p < 0.01). Bonferroni-adjusted post-hoc comparisons showed that feedback conditions differed from baseline as well as the new cadence conditions, however did not differ from each other. A significant interaction effect (region x feedback) was found for plantar loads (maximum force P < 0.001). Significant effects of feedback were noted at the heel (P < 0.001), medial midfoot (P < 0.001), lateral midfoot (P < 0.001), medial forefoot (P = 0.003), central forefoot (P = 0.003), and great toe (P = 0.004) but not at the lateral forefoot (P = 0.6) or lateral toes (P = 0.507).

SIGNIFICANCE

The unique findings of our study showed that an anterior shift of the center of pressure, particularly when foot strike modification was combined with 10% increased cadence. We found lower heel and midfoot loads along with higher forefoot and great toe loads when foot strike modification using real-time feedback was combined with increased cadence. Our findings also suggest that auditory feedback might be more effective than visual feedback in foot-strike modification.

SPATIOTEMPORAL COMPARISON OF OVERGROUND AND TREADMILL RUNNING WITH PRESSURE SENSOR INSOLES IN DIVISION I COLLEGIATE RUNNERS

STUDY DESIGN

Repeated measures.

BACKGROUND

Both clinicians and researchers often utilize treadmills to analyze spatiotemporal and biomechanical factors during running. However, there is question of whether or not treadmill running mimics overground running. The development of new wearable technology, such as pressure sensor insoles, presents an opportunity to compare the two running conditions.

PURPOSE

To compare the spatiotemporal factors between overground and treadmill running in collegiate runners, using pressure sensor insoles.

METHODS

Twenty-one collegiate runners (age 20.1 ± 1.5 years, 81% female) were recruited from a Division I Cross Country team. Subjects participated in two 15-minute testing sessions. During the first session, subjects ran at their "easy run pace" for 200 meters, while wearing pressure sensor insoles. During the second session, subjects ran at a speed-matched pace on a treadmill for one minute at a level grade, and one minute at a 1% incline. Cadence, stance duration and swing duration were processed using Moticon Science Pro + software (Munich, DE). Data between overground and treadmill running was compared using repeated measures analysis of variance with α = 0.05.

RESULTS

Compared to overground running, level and incline treadmill running was associated with increased cadence (mean difference [MD] = 3.55-3.22 strides per minute; p < 0.01), decreased stance duration (MD = 14-16 ms; p < 0.01), and decreased swing duration (MD = 11-12 ms; p < 0.05).

CONCLUSION

In collegiate runners, overground and treadmill running differ in spatiotemporal comparisons.

LEVELS OF EVIDENCE

3.

The relationship between performance and biomechanics in middle-distance runners

The present study aimed to identify movement patterns most related to running performance among highly trained middle-distance runners. Eleven male runners performed overground running trials on an indoor running track, and three-dimensional analyses techniques were used to measure running kinematics and kinetics. Performance was measured as season and personal best time over 1500 m. The average velocity during the running trials was 7.2 ± 0.3 m/s. The average season and personal best 1500 m race times were 3:49.7 ± 0:05.8 and 3:46.0 ± 0:08.3 minutes, respectively. Regression analysis revealed that a smaller range of sagittal-plane hip motion during swing, less thorax flexion at toe-off and a smaller ankle plantarflexion angle at contact accounted for 95.7% (p < 0.001) of the variation in season best running performance. Less sagittal-plane hip motion during swing and a smaller ankle plantarflexion angle at contact also explained 79% of the variance in personal best time. Slower middle-distance runners make initial ground contact with a more plantarflexed ankle and greater forward lean of the trunk. We recommend that coaches and runners pay attention to ankle, shank and thorax angles during technical development and training to identify opportunities to optimise middle-distance running mechanics and performance.

Cadence impact on cardiopulmonary, metabolic and biomechanical loading during downhill running

BACKGROUND

Distance runners can approach long descents with slow cadence and long steps, or a fast cadence with shorter steps. These approaches differentially affect mechanical loading and energy demand.

RESEARCH QUESTION

This study determined the cadence range in which biomechanical loads, caloric unit cost and energy cost were simultaneously minimized during downhill running (DR).

METHODS

Trained runners (N = 40; 25.6 ± 7.2 yr; 42.5% female) participated in this experimental study. Participants ran on an instrumented treadmill while wearing a portable gas analyzer during six conditions: control normal level running (LR) at 0 deg inclination (CON-0); control DR -6 deg inclinaton (CON-6); DR at cadences +/-5% and +/-10% different from CON-6. A motion analysis system was used to capture running motion, and an instrumented treadmill captured force data. Cardiopulmonary measures, rating of perceived exertion (RPE), and biomechanical measures (temporal spatial parameters, peak ground reaction forces [GRF], vertical average loading rate [VALR], impulses) were calculated. Caloric unit cost and energy costs were standardized per unit distance.

RESULTS

Running at -10% cadence increased HR by 10 bpm compared to CON-6 (p < 0.0001). Vertical excursion of the center of mass and step length were greatest in the cadence -10% and least in the cadence +10% conditions (both p < 0.0001). RPEs were higher among all cadence conditions compared to CON-0 (p < 0.0001). Caloric unit costs were lowest in CON-6, and +/5% cadence conditions compared to the CON-0 and +/-10% conditions (-2.1% to -12.3%, respectively; p < 0.05). Peak GRF and VALR were not different among conditions; vertical impulses were greatest in the -10% condition compared to CON-0, CON-6 and +5% and +10% by 11.3-14.5% (p < .001).

SIGNIFICANCE

Changing cadence across level and downhill stretches is likely not necessary and may actually increase perceived effort of running. Running downhill at cadences that range +/-5% of preferred simultaneously minimize caloric unit cost and impulse loading.

The stability of step rate throughout a 3200 meter run

Step rate has been studied in controlled laboratory settings due to its association with biomechanical parameters related to running injuries. However, the stability of step rate in a run over ground when speed is not controlled remains unclear. In this observational cohort study, 30 subjects were asked to run 3200 meters (m) over ground at their self-selected pace during an Army Physical Fitness Test. Stationary cameras were placed along the paved course to capture step rate at 800 m, 1200 m, 1800 m, and 2200 m. For analysis of step rate at four different time points, a repeated measures analysis of variance (ANOVA) with a Bonferroni-Holm correction was utilized to determine statistical difference with a significance level set at p < 0.05 (95% confidence intervals). There was a statistically significant (p = 0.04) difference between step rate at two different time points; however, the mean group difference in step rate was approximately 1-2 steps per minute, which is not likely clinically meaningful. There was no difference in average weekly miles trained or performance time in those who demonstrated a change in step rate versus those who maintained a steady step rate. Clinicians and researchers may be able to expect step rate to be consistent from 800 m-2200 m during a 3200 m timed run regardless of the runner's training mileage or performance time. This may be valuable for observing over ground running characteristics when the full course of a run cannot be viewed as it could within a laboratory setting.

Overuse injuries in runners of different abilities-a one-year prospective study

The aim of this prospective study was to investigate differences in participant characteristics, previous injury, running dynamics during a long-distance run, and training between injured and uninjured runners in runners of different abilities. Center-of-mass acceleration data were collected during a long-distance overground run. Runners were then divided into four groups (elite, advanced, intermediate and slow) based on their finishing time. Participants completed training diaries and were monitored for 1 year. Seventy-six runners completed the prospective study with 39 (51.3%) sustaining a running injury (44% elite, 42% advanced, 54% intermediate, 59% slow). Differences between injured and uninjured runners within each group related to injury included: (1) elite injured runners ran with longer contact times and (2) more slow injured runners reported an injury in previous year, were heavier, had higher body mass and body mass index, ran with lower step frequencies, and ran a greater weekly distance. Advanced injured runners exhibited fatigue changes in step regularity and peak braking during the run that may be related to injury. These findings suggest that runners of different abilities may have different factors related to injury however due to the small sample sizes in the groups this needs to be explored further.

Skipping has lower knee joint contact forces and higher metabolic cost compared to running

BACKGROUND

The health benefits of running based exercise programs are plentiful however the high rate of injury in these programs often reduces or eliminates exercise participation. Skipping has shorter steps, reduced vertical ground reaction forces (GRFs), and lower knee extensor torques, compared to running forming the basis of the present hypothesis that skipping would have lower tibio-femoral and patello-femoral joint contact forces.

RESEARCH QUESTION

The purpose of this study was to compare knee contact forces between skipping and running at the same speed. We also compared metabolic cost of these two gaits to examine the idea that the larger vertical displacement in skipping is a primary factor in its previously reported high metabolic cost.

METHODS

The study evaluated joint contact forces through musculoskeletal modeling with GRF and 3D kinematic data and metabolic cost using oxygen consumption data from 20 young, healthy, trained participants as they skipped and ran on an instrumented treadmill at 2.68 m/s.

RESULTS

Skipping, compared to running, had substantially lower tibio-femoral and patello-femoral joint contact forces and linear impulses on both per-step and per-kilometer (i.e. lower cumulative loads) bases and also 30% higher metabolic cost. The lower joint loads in skipping were directly associated with its shorter steps and the higher metabolic cost was directly associated to its larger vertical displacement through the stride.

SIGNIFICANCE

As joint loads may predispose individuals to running related injuries, skipping presents an attractive alternative exercise modality with additional increased aerobic benefits.

Relationships between Habitual Cadence, Footstrike, and Vertical Load Rates in Runners

Excessive vertical ground reaction force (VGRF) load rates have been linked with running injuries. Increasing cadence (CAD) has been shown to reduce load rates; however, relationships between habitual cadence and load rates across a population of runners have not been examined.

PURPOSE

To examine the relationships between habitual running cadence and vertical load rates in healthy and injured runners using habitual footstrike patterns. As CAD increased, we expected vertical load rates would decrease.

METHODS

Healthy runners (n = 32, 25 men) and injured runners (n = 93, 45 men) seeking treatment were analyzed. Footstrike classifications were heel at initial contact (rearfoot strike [RFS]) or forefoot at initial contact (forefoot strike [FFS]). Runners were divided into four injury status/footstrike pattern (FSP) subgroups: healthy RFS (n = 19), injured RFS (n = 70), healthy FFS (n = 13), and injured FFS (n = 23). The VGRF and CAD were recorded as participants ran on an instrumented treadmill at self-selected speed (x¯ = 2.6 m·s ±0.12). Healthy runners used laboratory footwear similar to their habitual footwear, and injured runners used habitual footwear. The vertical average load rates and vertical instantaneous load rates of the VGRF of each runner's right leg were calculated and correlated with CAD for four injury status-FSP subgroups and for all runners combined.

RESULTS

There were no differences in CAD between all runners or any subgroup (P > 0.05). Vertical average load rates and vertical instantaneous load rates were significantly higher (P ≤ 0.01) in the injured RFS group compared with all other subgroups. Injured FFS and healthy FFS had similar load rates (P = 1.0).

CONCLUSIONS

We found no relationships between habitual running cadence and vertical load rates. The highest load rates were in injured RFS runners, and the lowest load rates were in FFS runners, regardless of injury status. Future studies of gait retraining to increase CAD and reduce load rates should follow runners long term to examine this relationship once CAD has become habituated.

Years of running experience influences stride-to-stride fluctuations and adaptive response during step frequency perturbations in healthy distance runners

RESEARCH QUESTION

The current study investigated stride-to-stride fluctuations of step rate and contact time in response to enforced step frequency perturbations as well as adaptation and de-adaptation behavior.

METHODS

Forty distance runners ran at a self-selected speed and were asked to match five different enforced step frequencies (150, 160, 170, 180, and 190 beats per min). The influence of experience was explored, because running is a skill that presumably gets better with practice, and increased years of running experience is protective against injury. Detrended fluctuation analysis was used to determine the strength of long-range correlations in gait fluctuations at baseline, during the perturbation, and post-perturbation. Adaptive response was measured by the ability to match, rate of matching, and aftereffect of step frequency perturbations.

RESULTS

The structure of stride-to-stride fluctuations for step rate and contact time did not change during the perturbation or post-perturbation compared to baseline. However, fluctuations in step rate were affected by the level of perturbation. Runners with the most experience had a less persistent structural gait pattern for both step rate and contact time at baseline. Highly experienced runners also demonstrated the best adaptive response. They better matched the enforced step frequency, reached the enforced step frequency sooner, and returned to preferred step frequency more quickly following removal of the perturbation.

SIGNIFICANCE

These findings indicate baseline locomotor flexibility may be beneficial to achieve task demands and return to a stable state once the task is complete. Increased locomotor flexibility may also be a contributing factor for reduced injury risk in experienced runners.

Youth Distance Running: Strategies for Training and Injury Reduction

Running is a popular sport for children in the United States. However, review of available literature on health effects and safety recommendations for youth running has not been previously conducted. Unique factors for injury include periods of growth during puberty and potential for growth plate injury. Youth runners may benefit from activities that incorporate high-impact loading and multidirectional movement for optimal bone maturation, exercises to strengthen tendons and muscles, and strategies aimed at improving running biomechanics to reduce risk of injury. In addition, addressing lifestyle factors, including nutrition and sleep is essential for a runner's general health. Similar to other sports, sports specialization should not be encouraged in youth runners. Reducing running-related injury in growing children and assessing readiness for running should be based on a combination of physical, emotional, psychological, social, and cognitive factors. Youth runners require individualized training and competition to safely participate in the sport.

Transfer Learning Effects of Biofeedback Running Retraining in Untrained Conditions

PURPOSE

Running gait retraining via peak tibial shock biofeedback has been previously shown to reduce impact loading and mitigate running-related symptoms. In previous research, peak tibial shock is typically measured and trained for one limb at a single constant training speed during all training sessions. The goal of this study was to determine how runners transfer learning in the trained limb to the untrained limb at different unconstrained speeds.

METHODS

Thirteen runners (3 females, age = 41.1 ± 6.9 yr, running experience = 6.8 ± 4.4 yr, weekly running distance = 30.7 ± 22.2 km) underwent running gait biofeedback retraining via continuous tibial acceleration measured at the right distal tibia. Before and after the training, participants were asked to run at their self-selected constrained training speeds (2.8 ± 0.2 m·s) and at 110% and 90% of the training speed. Pretraining and posttraining peak tibial shock values for each limb were compared.

RESULTS

Participants reduced peak tibial shock in the trained limb by 35% to 37% (P < 0.05, Cohen's d = 0.78-0.85), and in the untrained limb by 20% to 23% (P < 0.05, Cohen's d = 0.51-0.71) across the three testing speeds. The reduction was not significantly different between the trained and untrained limbs (P = 0.31-0.79, Cohen's d = 0.18-0.45). Similarly, there was no difference in peak tibial shock reduction among the three running speeds (P = 0.48-0.61, Cohen's d = 0.06-0.45).

CONCLUSION

Participants demonstrated transfer learning effects evidenced by concomitant reduced peak tibial shock in the untrained limb, and the learning effects were retrained when running at a 10% variance of the training speed.

Is Cadence Related to Leg Length and Load Rate?

BACKGROUND

Increasing cadence is often recommended to reduce load rate and to lower injury risk. However, habitual cadence was recently shown to be unrelated to load rate. Cadence is likely influenced by leg length. If so, then cadence may be related to load rate when it is normalized to leg length.

OBJECTIVES

To examine the relationship between cadence and leg length in both injured and uninjured runners with a rearfoot strike pattern. We hypothesized that increased leg length would be associated with lower cadence. We also evaluated the relationship between cadence normalized to leg length and the vertical average load rate (VALR), expecting that as cadence normalized to leg length increased, VALR would decrease.

METHODS

In this cross-sectional cohort, laboratory-based study, 40 uninjured and 42 injured recreational runners with a rearfoot strike pattern were measured at self-selected speeds. The relationship of cadence to leg length was measured between groups by injury status. A secondary analysis evaluated the relationship between cadence normalized to leg length and VALR. The data were analyzed using a multiple linear regression, with injury status as a covariate. Alpha was set to .05.

RESULTS

Accounting for injury status, leg length had a moderate negative association with cadence (P<.001, r = 0.449, standardized β = - 0.443). There were no associations of VALR with cadence normalized to leg length by injury status or across participants.

CONCLUSION

Lower cadence was observed in recreational runners with longer legs, regardless of injury status. However, cadence was not related to load rate when normalized to leg length. J Orthop Sports Phys Ther 2019;49(4):280-283. doi:10.2519/jospt.2019.8420.

Real-Time Biofeedback of Performance to Reduce Braking Forces Associated With Running-Related Injury: An Exploratory Study

BACKGROUND

The high rate of running-related injury may be associated with increased peak braking forces (PBFs) and vertical loading rates. Gait retraining has been suggested by some experts to be an effective method to reduce loading parameters.

OBJECTIVES

To investigate whether PBF could be decreased following an 8-session gait retraining program among a group of female recreational runners and which self-selected kinematic strategies could achieve this decrease.

METHODS

In this exploratory study, 12 female recreational runners with high PBFs (greater than 0.27 body weight) completed an 8-session gait retraining program with real-time biofeedback of braking forces over the course of a half-marathon training program. Baseline and follow-up kinetics and kinematics were analyzed with a repeated-measures analysis of variance.

RESULTS

There was an average reduction of 15% in PBF (-0.04 body weight; 95% confidence interval [CI]: -0.07, -0.02 body weight; P = .001; effect size, 0.62), accompanied by a 7% increase in step frequency (11.3 steps per minute; 95% CI: 1.8, 20.9 steps per minute; P = .024; effect size, 0.38) and a 6% decrease in step length (-5.5 cm; 95% CI: -9.9, -1.0 cm; P = .020; effect size, 0.40), from baseline to follow-up.

CONCLUSION

The gait retraining program significantly reduced the PBF among a group of female recreational runners. This was achieved through a combination of increased step frequency and decreased step length. Furthermore, the modified gait pattern was incorporated into the runners' natural gait pattern by the completion of the program. Based on these results, the outlined gait retraining program should be further investigated to assess whether it may be an effective injury prevention strategy for recreational runners. This study was registered with ClinicalTrials.gov (NCT03302975).

LEVEL OF EVIDENCE

Prevention, level 4. J Orthop Sports Phys Ther 2019;49(3):136-144. Epub 7 Dec 2018. doi:10.2519/jospt.2019.8587.

Tibiofemoral Joint Forces in Female Recreational Runners Vary with Step Frequency

PURPOSE

Elevated tibiofemoral joint (TFJ) contact forces have been linked to the development and progression of knee osteoarthritis. The primary objective of this study was to determine the association between peak TFJ shear and compression forces during running at different self-selected step frequencies (SF) in female recreational runners.

METHODS

Fifty-five healthy female recreational runners ran at 2.98 m·s on an instrumented treadmill. Peak TFJ anterior shear force, peak axial TFJ compression force, and peak medial compartment TFJ compression force were estimated using a musculoskeletal model with inputs from 3D joint kinematics and inverse dynamics calculations. Three SF groups were generated using tertiles, and differences between the groups were compared using one-way ANOVA (α = 0.05).

RESULTS

Runners with an SF of ≥178 steps per minute demonstrated the lowest peak TFJ anterior shear force (P = 0.04), peak axial TFJ compression force (P = 0.01), and peak TFJ medial compartment compression forces (P = 0.01) compared with runners using lower SF.

CONCLUSION

Female recreational runners with low SF of ≤166 steps per minute experience greater TFJ contact forces. This study provides evidence of an association between SF and both shear and axial peak TFJ contact forces during running.

Patellofemoral joint stress measured across three different running techniques

BACKGROUND

Patellofemoral pain (PFP) is the most common running-related injury. It has been shown in previous studies that gait retraining may have a beneficial effect on patellofemoral joint stress (PFJS).

RESEARCH QUESTION

Is there a reduction of PFJS across 4 running conditions: 1. runner's typical rearfoot strike pattern, 2. forefoot landing, 3. step rate increase by 10% and 4. forward trunk lean?

METHODS

Nineteen healthy runners (28.05 ± 5.03 years; 26.58 ± 8.85 km/week, 6.00 ± 4.51 years of running experience) completed one running trial for each condition, at the same subject-specific comfortable speed on a treadmill. Kinetic and kinematic data were collected and measures of hip, knee and ankle joint moments and PFJS were calculated.

RESULTS

Compared to rearfoot strike condition, peak PFJS and PFJS-time integral per step were significantly (P < 0.01) lower during forefoot landing and step rate increase conditions. PFJS per kilometer was significantly reduced for forefoot landing (17.01%; P < 0.01) and increased step rate (12.90%; P = 0.003). Forward trunk lean technique showed no significant differences in peak PFJS (P = 0.187), PFJS-time integral per step (P = 0.815) and PFJS per kilometer (P = 0.077) compared to rearfoot strike pattern.

INTERPRETATION

The comparison between techniques revealed greater reductions on PFJS by forefoot landing, followed by 10% step rate increase condition. These changes were the result of different lower limb movement strategies across the 2 running conditions. We conclude that compared to a rearfoot strike pattern, both a forefoot landing and step rate increase result in lower cumulative PFJS joint stress in healthy runners, with the forefoot landing being the most effective. These running technique modifications could be recommended to reduce PFJS loads and may have implications for PFP prevention.

Step frequency patterns of elite ultramarathon runners during a 100-km road race

Step frequency (SF) in running has received substantial interest from researchers, coaches, therapists, and runners. It has been widely studied in controlled settings, but no published study has measured it continuously in elite-level competition. The present study used wrist-based accelerometers in consumer-grade watches to monitor SF and SF variability of competitors in the 2016 100-km World Championship road race. Using linear mixed-model regression, SF and SF variability were assessed across the race. The average SF (steps-per-minute) of competitors ( n = 20) was 182.0 spm (range: 155.4-203.1 spm). Race fluctuations in SF were influenced only by the speed the competitors were running, with faster speeds being associated with greater SF (5.6 spm/m·s^-1, P < 0.001). Independently of this speed relation, SF did not significantly change over the course of the race. SF was further linked to the runner's stature (-123.1 spm/m, P = 0.01) but not significantly related to sex, weight, age, or years of experience. The SF coefficient-of-variation was inversely associated with running speed and distance covered, with runners demonstrating decreasing variability both at faster speeds and as the race progressed. Together, these results add ecological evidence to observations of a speed dependency of SF in a highly trained, elite population of runners and suggest that in road race conditions, SF changes only with speed and not fatigue. Furthermore, it presents evidence that the variability of an elite runner's SF is linked to both speed and fatigue but not to any other characteristics of the runner. The current findings are important for runners, clinicians, and coaches as they seek to monitor or manipulate SF. NEW & NOTEWORTHY Stride frequency (SF; or the synonymous "cadence") has become a popular point of monitoring and manipulation in runners. Advances in wearable technology have enabled continuous monitoring of SF. This study is the first to examine SF and SF variability patterns throughout an entire road race in elite ultramarathon runners. This adds ecological, normative data to the field's understanding of SF and demonstrates how it relates to running speed, fatigue, and individual characteristics.

Kinematic Correlates of Kinetic Outcomes Associated With Running-Related Injury

High magnitudes and rates of loading have been implicated in the etiology of running-related injuries. Knowledge of kinematic variables that are predictive of kinetic outcomes could inform clinic-based gait retraining programs. Healthy novice female runners ran on a treadmill while 3-dimensional biomechanical data were collected. Kinetic outcomes consisted of vertical impact transient, average vertical loading rate, instantaneous vertical loading rate, and peak braking force. Kinematic outcomes included step length), hip flexion angle at initial contact, horizontal distance from heel to center of mass at initial contact, shank angle at initial contact, and foot strike angle. Stepwise multiple linear regression was used to evaluate the amount of variance in kinetic outcomes explained by kinematic outcomes. A moderate amount of variance in kinetic outcomes (vertical impact transient = 46%, average vertical loading rate = 37%, instantaneous vertical loading rate = 49%, peak braking force = 54%) was explained by several discrete kinematic variables-predominantly speed, horizontal distance from heel to center of mass, foot strike angle, and step length. Hip flexion angle and shank angle did not contribute to any models. Decreasing step length and transitioning from a rearfoot strike may reduce kinetic risk factors for running-related injuries. In contrast, clinical strategies such as modifying shank angle and hip flexion angle would not appear to contribute significantly to the variance of kinetic outcomes after accounting for other variables.

Validity of a novel method to measure vertical oscillation during running using a depth camera

Recent advancements in low-cost depth cameras may provide a clinically accessible alternative to conventional three-dimensional (3D) multi-camera motion capture systems for gait analysis. However, there remains a lack of information on the validity of clinically relevant running gait parameters such as vertical oscillation (VO). The purpose of this study was to assess the validity of measures of VO during running gait using raw depth data, in comparison to a 3D multi-camera motion capture system. Sixteen healthy adults ran on a treadmill at a standard speed of 2.7 m/s. The VO of their running gait was simultaneously collected from raw depth data (Microsoft Kinect v2) and 3D marker data (Vicon multi-camera motion capture system). The agreement between the VO measures obtained from the two systems was assessed using a Bland-Altman plot with 95% limits of agreement (LOA), a Pearson's correlation coefficient (r), and a Lin's concordance correlation coefficient (r_c). The depth data from the Kinect v2 demonstrated excellent results across all measures of validity (r = 0.97; r_c = 0.97; 95% LOA = -8.0 mm - 8.7 mm), with an average absolute error and percent error of 3.7 (2.1) mm and 4.0 (2.0)%, respectively. The findings of this study have demonstrated the ability of a low cost depth camera and a novel tracking method to accurately measure VO in running gait.

Biomechanics of single-leg running using lofstrand crutches in amputee soccer

[Purpose] Amputee soccer is a game for individuals with amputations. Players use lofstrand crutches to move around the field and kick the ball. Scoring quick goals during a match requires players to have maximum running skills. Notably, a few parameters affect the running speed in players; however, no study has reported the biomechanical analysis of running in amputee soccer. Thus study aimed to analyze the biomechanics of single-leg running using lofstrand crutches in 12 healthy adult males (6 with prior amputee soccer experience and 6 without such experience). [Participants and Methods] The kinematics of the lower limb and the pelvis, the ground reaction force, and skill in using the crutches were evaluated using 3 dimensional motion analysis combined with 8 force plates. Lower leg amputation was simulated in all participants by maintaining the non-dominant knee in a position of maximum flexion using an elastic band. [Results] Significant differences were observed between experienced and non-experienced participants with regard to the angle of the pelvis and the crutch stance phase. Specifically, higher running speed was associated with an increased forward tilt of the pelvis and a shorter crutch stance phase. [Conclusion] These findings will be useful to improve the running speed of amputee soccer players.

The biomechanical characteristics of high-performance endurance running

The biomechanical profile of high-level endurance runners may represent a useful model that could be used for developing training programmes designed to improve running style. This study, therefore, sought to compare the biomechanical characteristics of high-performance and recreational runners. Kinematic and kinetic measurements were taken during overground running from a cohort of 14 high-performance (8 male) and 14 recreational (8 male) runners, at four speeds ranging from 3.3 to 5.6 m s^-1. Two-way ANOVA analysis was then used to explore group and speed effects and principal component analysis used to explore the interdependence of the tested variables. The data showed the high-performance runners to have a gait style characterised by an increased vertical velocity of the centre of mass and a flight time that was 11% longer than the recreational group. The high-performance group were also observed to adopt a forefoot strike pattern, to contact the ground with their foot closer to their body and to have a larger ankle moment. Importantly, although observed group differences were mostly independent of speed, the tested variables showed a high degree of interdependence suggesting an underlying unitary phenomenon. This is the first study to compare high-performance and recreational runners across a full range of kinematic and kinetic variables. The results suggest that high-performance runners maintain stride length with a prolonged aerial phase, rather than by landing with a more extended knee. These findings motivate future intervention studies that should investigate whether recreational runners could benefit from instruction to decrease shank inclination at foot contact.

Four weeks of training with simple postural instructions changes trunk posture and foot strike pattern in recreational runners

OBJECTIVES

Previous studies showed that adopting forward trunk lean and forefoot strike patterns may reduce risk of running-related knee injuries. However, the process of learning such forms is unclear. The purpose of the study was to investigate the effects of a 4-week training using simple postural instructions to elicit these changes.

DESIGN

Longitudinal intervention study.

SETTING

A training included postural instructions: 1) lean your trunk forward, and 2) land on the front part of your feet.

PARTICIPANTS

Eighteen recreational runners.

MAIN OUTCOME MEASURES

Participants were assessed prior to training (PRE), immediately after the instructions (iPST), during training at 2 weeks (2WK) and 4 weeks (4WK), and 7-10 days after the conclusion of training (RET). Assessment consisted of running trials performed at self-selected and controlled speeds, during which the trunk and foot strike angles were assessed.

RESULTS

Comparing to PRE, forward trunk angle significantly increased by approximately 3.5° and foot strike angle by approximately 7° at 2WK, 4WK and RET.

CONCLUSIONS

A 4-week training with simple postural instructions induced significant changes in trunk and foot strike patterns in recreational runners. Future study is needed to develop clinical therapeutic protocols for runners with and at risk of running-related knee injuries.

A New Direction to Athletic Performance: Understanding the Acute and Longitudinal Responses to Backward Running

Backward running (BR) is a form of locomotion that occurs in short bursts during many overground field and court sports. It has also traditionally been used in clinical settings as a method to rehabilitate lower body injuries. Comparisons between BR and forward running (FR) have led to the discovery that both may be generated by the same neural circuitry. Comparisons of the acute responses to FR reveal that BR is characterised by a smaller ratio of braking to propulsive forces, increased step frequency, decreased step length, increased muscle activity and reliance on isometric and concentric muscle actions. These biomechanical differences have been critical in informing recent scientific explorations which have discovered that BR can be used as a method for reducing injury and improving a variety of physical attributes deemed advantageous to sports performance. This includes improved lower body strength and power, decreased injury prevalence and improvements in change of direction performance following BR training. The current findings from research help improve our understanding of BR biomechanics and provide evidence which supports BR as a useful method to improve athlete performance. However, further acute and longitudinal research is needed to better understand the utility of BR in athletic performance programs.

Effects of footwear midsole thickness on running biomechanics

Shoe manufacturers launch running shoes with increased (e.g., maximalists) or decreased (e.g., minimalists) midsole thickness and claim that they may prevent running injury. Previous studies tested footwear models with different midsole thicknesses on the market but the shoe construct was not strictly comparable. Therefore, in the present study, we examined the effect of midsole thickness, from 1-mm to 29-mm, in a standard test shoe prototype on the vertical loading rates, footstrike angle and temporal spatial parameters in distance runners. Fifteen male habitual rearfoot strikers were recruited from local running clubs. They were asked to run on an instrumented treadmill in shoes with different midsole thicknesses. We found significant interactions between midsole thickness with vertical loading rates (p < 0.001), footstrike angle (p = 0.013), contact time (p < 0.001), cadence (p = 0.003), and stride length (p = 0.004). Specifically, shoes with thinner midsole (1- and 5-mm) significantly increased the vertical loading rates and shortened the contact time, when compared with thicker midsole shoes (25- and 29-mm). However, we did not observe any substantial differences in the footstrike angle, cadence and stride length between other shod conditions. The present study provides biomechanical data regarding the relationship between full spectrum midsole thicknesses and running biomechanics in a group of rearfoot strikers.