Manipulation of Foot Strike and Footwear Increases Achilles Tendon Loading During Running

Recent Innovations in Footwear and the Role of Smart Footwear in Healthcare-A Survey

Smart shoes have ushered in a new era of personalised health monitoring and assistive technologies. Smart shoes leverage technologies such as Bluetooth for data collection and wireless transmission, and incorporate features such as GPS tracking, obstacle detection, and fitness tracking. As the 2010s unfolded, the smart shoe landscape diversified and advanced rapidly, driven by sensor technology enhancements and smartphones' ubiquity. Shoes have begun incorporating accelerometers, gyroscopes, and pressure sensors, significantly improving the accuracy of data collection and enabling functionalities such as gait analysis. The healthcare sector has recognised the potential of smart shoes, leading to innovations such as shoes designed to monitor diabetic foot ulcers, track rehabilitation progress, and detect falls among older people, thus expanding their application beyond fitness into medical monitoring. This article provides an overview of the current state of smart shoe technology, highlighting the integration of advanced sensors for health monitoring, energy harvesting, assistive features for the visually impaired, and deep learning for data analysis. This study discusses the potential of smart footwear in medical applications, particularly for patients with diabetes, and the ongoing research in this field. Current footwear challenges are also discussed, including complex construction, poor fit, comfort, and high cost.

Achilles Tendon Loading during Running Estimated Via Shear Wave Tensiometry: A Step Toward Wearable Kinetic Analysis

PURPOSE

Understanding muscle-tendon forces (e.g., triceps surae and Achilles tendon) during locomotion may aid in the assessment of human performance, injury risk, and rehabilitation progress. Shear wave tensiometry is a noninvasive technique for assessing in vivo tendon forces that has been recently adapted to a wearable technology. However, previous laboratory-based and outdoor tensiometry studies have not evaluated running. This study was undertaken to assess the capacity for shear wave tensiometry to produce valid measures of Achilles tendon loading during running at a range of speeds.

METHODS

Participants walked (1.34 m·s -1 ) and ran (2.68, 3.35, and 4.47 m·s -1 ) on an instrumented treadmill while shear wave tensiometers recorded Achilles tendon wave speeds simultaneously with whole-body kinematic and ground reaction force data. A simple isometric task allowed for the participant-specific conversion of Achilles tendon wave speeds to forces. Achilles tendon forces were compared with ankle torque measures obtained independently via inverse dynamics analyses. Differences in Achilles tendon wave speed, Achilles tendon force, and ankle torque across walking and running speeds were analyzed with linear mixed-effects models.

RESULTS

Achilles tendon wave speed, Achilles tendon force, and ankle torque exhibited similar temporal patterns across the stance phase of walking and running. Significant monotonic increases in peak Achilles tendon wave speed (56.0-83.8 m·s -1 ), Achilles tendon force (44.0-98.7 N·kg -1 ), and ankle torque (1.72-3.68 N·m·(kg -1 )) were observed with increasing locomotion speed (1.34-4.47 m·s -1 ). Tensiometry estimates of peak Achilles tendon force during running (8.2-10.1 body weights) were within the range of those estimated previously via indirect methods.

CONCLUSIONS

These results set the stage for using tensiometry to evaluate Achilles tendon loading during unobstructed athletic movements, such as running, performed in the field.

Larger Achilles and plantar fascia induce lower duty factor during barefoot running

OBJECTIVES

Tendons play a crucial role allowing the storage and release of mechanical energy during the running cycle. Running kinematics, including duty factor, constitute a basic element of the runner's biomechanics, and can determine their performance. This study aimed to analyze the link between Achilles tendon and plantar fascia morphology and running parameters, considering the influence of wearing shoes versus running barefoot.

DESIGN

Cross-sectional study.

METHODS

44 participants (30 men and 14 women) engaged in two running sessions, one with shoes and one without, both lasting 3 min at a consistent speed of 12 km/h. We captured running kinematic data using a photoelectric cell system throughout the sessions. Before the trials, we measured the thickness and cross-sectional area of both the Achilles tendon and plantar fascia using ultrasound.

RESULTS

The Pearson test revealed a significant correlation (p < 0,05) between Achilles tendon and plantar fascia morphology and contact time (r > -0.325), flight time (r > -0.325) and duty factor (ratio of ground contact to stride time) (r > -0.328) during barefoot running. During the shod condition, no significant correlation was found between connective tissue morphology and kinematic variables.

CONCLUSIONS

In barefoot running, greater size of the Achilles tendon and plantar fascia results in a reduced duty factor, attributed to longer flight times and shorter contact times.

Morphological and viscoelastic properties of the Achilles tendon in the forefoot, rearfoot strike runners, and non-runners in vivo

The purpose of this study was to investigate the differences in the morphological and viscoelastic properties of the Achilles tendon (AT) among different groups (rearfoot strikers vs. forefoot strikers vs. non-runners). Thirty healthy men were recruited, including habitual forefoot strike runners (n = 10), rearfoot strike runners (n = 10), and individuals with no running habits (n = 10). The AT morphological properties (cross-sectional area and length) were captured by using an ultrasound device. The real-time ultrasound video of displacement changes at the medial head of the gastrocnemius and the AT junction during maximal voluntary isometric contraction and the plantar flexion moment of the ankle was obtained simultaneously by connecting the ultrasound device and isokinetic dynamometer via an external synchronisation box. The results indicated that male runners who habitually forefoot strike exhibited significantly lower AT hysteresis than male non-runners (p < 0.05). Furthermore, a greater peak AT force during maximal voluntary contraction was observed in forefoot strike male runners compared to that in male individuals with no running habits (p < 0.05). However, foot strike patterns were not related to AT properties in recreational male runners (p > 0.05). The lower AT hysteresis in male FFS runners implied that long-term forefoot strike patterns could enhance male-specific AT's ability to store and release elastic energy efficiently during running, resulting in a more effective stretch-shortening cycle. The greater peak AT force in male FFS runners indicated a stronger Achilles tendon.

Running-Related Achilles Tendon Injury: A Prospective Biomechanical Study in Recreational Runners

There are relatively few running studies that have attempted to prospectively identify biomechanical risk factors associated with Achilles tendon (AT) injuries. Therefore, the aim was to prospectively determine potential running biomechanical risk factors associated with the development of AT injuries in recreational, healthy runners. At study entry, 108 participants completed a set of questionnaires. They underwent an analysis of their running biomechanics at self-selected running speed. The incidence of AT running-related injuries (RRI) was assessed after 1-year using a weekly questionnaire standardized for RRI. Potential biomechanical risk factors for the development of AT RRI injury were identified using multivariable logistic regression. Of the 103 participants, 25% of the sample (15 males and 11 females) reported an AT RRI on the right lower limb during the 1-year evaluation period. A more flexed knee at initial contact (odds ratio = 1.146, P = .034) and at the midstance phase (odds ratio = 1.143, P = .037) were significant predictors for developing AT RRI. The results suggested that a 1-degree increase in knee flexion at initial contact and midstance was associated with a 15% increase in the risk of an AT RRI, thus causing a limitation of training or a stoppage of running in runners.

Achilles tendon dimensions, ankle stiffness and footfall patterns in recreational runners

The main purpose of this study was to investigate the relationship among Achilles tendon (AT) dimensions, ankle joint stiffness, and footfall patterns in recreational rearfoot and non-rearfoot runners. Based on the foot strike index, a total of 107 runners were divided into rearfoot (47 females/40 males) and non-rearfoot runners (14 females/6 males). All participants had theirs AT dimensions (AT length, AT thickness, and AT moment arm) measured using a combination of ultrasound and motion capture systems. In addition, all performed running trials measured at self-selected speed in laboratory-neutral shoes. A partial correlation coefficient was used for correlations between the selected variables. The results revealed a significant relationship between ankle joint stiffness and level of footfall pattern in rearfoot (r = 0.232, p = 0.032) and non-rearfoot runners (r = -0.811, p < 0.001). The results also suggest a relationship between AT thickness and foot strike index (r = -0.486) in non-rearfoot runners. Runners whose footfall pattern is closer to the heel have greater ankle joint stiffness. Non-rearfoot runners whose footfall pattern is closer to the toe have a thinner AT. Non-rearfoot runners with thicker AT had greater ankle joint stiffness.

Measurement and reporting of footwear characteristics in running biomechanics: A systematic search and narrative synthesis of contemporary research methods

This review aimed to synthesise the methods for assessing and reporting footwear characteristics among studies evaluating the effect of footwear on running biomechanics. Electronic searches of Scopus®, EBSCO, PubMed®, ScienceDirect®, and Web of Science® were performed to identify original research articles of the effect of running footwear on running biomechanics published from 1^st January 2015 to 7^th October 2020. Risk of bias among included studies was not assessed. Results were presented via narrative synthesis. Eligible studies compared the effect of two or more footwear conditions in adult runners on a biomechanical parameter. Eighty-seven articles were included and data from 242 individual footwear were extracted. Predominantly, studies reported footwear taxonomy (i.e., classification) and manufacturer information, however omitted detail regarding the technical specifications of running footwear and did not use validated footwear reporting tools. There is inconsistency among contemporary studies in the methods by which footwear characteristics are assessed and reported. These findings point towards a need for consensus regarding the reporting of these characteristics within biomechanical studies to facilitate the conduct of systematic reviews and meta-analyses pertaining to the effect of running footwear on running biomechanics.

Isolated effects of footwear structure and cushioning on running mechanics in habitual mid/forefoot runners

The true differences between barefoot and shod running are difficult to directly compare because of the concomitant change to a mid/forefoot footfall pattern that typically occurs during barefoot running. The purpose of this study was to compare isolated effects of footwear structure and cushioning on running mechanics in habitual mid/forefoot runners running shod (SHOD), barefoot (BF), and barefoot on a foam surface (BF+FOAM). Ten habitually shod mid/forefoot runners were recruited (male = 8, female = 2). Repeated measures ANOVA (α = 0.05) revealed differences between conditions for only vertical peak active force, contact time, negative and total ankle joint work, and peak dorsiflexion angle. Post hoc tests revealed that BF+FOAM resulted in smaller vertical active peak magnitude and instantaneous vertical loading rate than SHOD. SHOD resulted in lower total ankle joint work than BF and BF+FOAM. BF+FOAM resulted in lower negative ankle joint work than either BF or SHOD. Contact time was shorter with BF than BF+FOAM or SHOD. Peak dorsiflexion angle was smaller in SHOD than BF. No other differences in sagittal joint kinematics, kinetics, or ground reaction forces were observed. These overall similarities in running mechanics between SHOD and BF+FOAM question the effects of footwear structure on habituated mid/forefoot running described previously.

The load borne by the Achilles tendon during exercise: A systematic review of normative values

The Achilles tendon (AT) can be exposed to considerable stress during athletic activities and is often subject to pathologies such as tendinopathies. When designing a prevention or rehabilitation protocol, mechanical loading is a key factor to consider. This implies being able to accurately determine the load applied to the AT when performing exercises that stress this tendon. A systematic review was performed to synthesize the load borne by the AT during exercises/activities. Three databases (Pubmed, Embase and Cochrane) were searched for articles up to May 2021, and only the studies assessing the AT load in newtons relative to body-weight (BW) on humans during activities or exercises were included. Most of the 11 included studies assessed AT load when running or walking (N = 10), and only three tested exercises were usually performed during rehabilitation. The load on the tendon ranged from 2.7 to 3.95 BW when walking, from 4.15 to 7.71 BW when running, and from 0.41 to 7.3 BW according to the strengthening exercise performed. From the collected data, a progression of exercises progressively loading the Achilles tendon, as well as the possible connections with walking and running activities, could be defined. However, the trends highlighted in the relationship between tendon loading and walking or running speeds present some inconsistencies. Further research is still needed to clarify them, but also to complete the data set in healthy and injured people.

Leaning the Trunk Forward Decreases Patellofemoral Joint Loading During Uneven Running

ABSTRACT

AminiAghdam, S, Epro, G, James, D, and Karamanidis, K. Leaning the trunk forward decreases patellofemoral joint loading during uneven running. J Strength Cond Res 36(12): 3345-3351, 2022-Although decline surfaces or a more upright trunk posture during running increase the patellofemoral joint (PFJ) contact force and stress, less is known about these kinetic parameters under simultaneous changes to the running posture and surface height. This study aimed to investigate the interaction between Step (10-cm drop-step and level step) and Posture (trunk angle from the vertical: self-selected, ∼15°; backward, ∼0°; forward, ∼25°) on PFJ kinetics (primary outcomes) and knee kinematics and kinetics as well as hip and ankle kinetics (secondary outcomes) in 12 runners at 3.5 ms -1 . Two-way repeated measures analyses of variance ( α = 0.05) revealed no step-related changes in peak PFJ kinetics across running postures; however, a decreased peak knee flexion angle and increased joint stiffness in the drop-step only during backward trunk-leaning. The Step main effect revealed significantly increased peak hip and ankle extension moments in the drop-step, signifying pronounced mechanical demands on these joints. The Posture main effect revealed significantly higher and lower PFJ kinetics during backward and forward trunk-leaning, respectively, when compared with the self-selected condition. Forward trunk-leaning yielded significantly lower peak knee extension moments and higher hip extension moments, whereas the opposite effects occurred with backward trunk-leaning. Overall, changes to the running posture, but not to the running surface height, influenced the PFJ kinetics. In line with the previously reported efficacy of forward trunk-leaning in mitigating PFJ stress while even or decline running, this technique, through a distal-to-proximal joint load redistribution, also seems effective during running on surfaces with height perturbations.

Effects of a 12-week gait retraining program combined with foot core exercise on morphology, muscle strength, and kinematics of the arch: A randomized controlled trial

Objective: This study aims to explore the effects of a 12-week gait retraining program combined with foot core exercise on arch morphology, arch muscles strength, and arch kinematics. Methods: A total of 26 male recreational runners with normal arch structure who used rear-foot running strike (RFS) were divided into the intervention group (INT group) and control group (CON group) (n = 13 in each group). The INT group performed a 12-week forefoot strike (FFS) training combined with foot core exercises. The CON group did not change the original exercise habit. Before and after the intervention, the arch morphology, as well as the strength of hallux flexion, lesser toe flexion, and the metatarsophalangeal joint (MPJ) flexors were measured in a static position, and changes in the arch kinematics during RFS and FFS running were explored. Results: After a 12-week intervention, 1) the normalized navicular height increased significantly in the INT group by 5.1% (p = 0.027, Cohen's d = 0.55); 2) the hallux absolute flexion and relative flexion of the INT group increased significantly by 20.5% and 21.7%, respectively (p = 0.001, Cohen's d = 0.59; p = 0.001, Cohen's d = 0.73), the absolute and relative strength of the MPJ flexors of the INT group were significantly improved by 30.7% and 32.5%, respectively (p = 0.006, Cohen's d = 0.94; p = 0.006, Cohen's d = 0.96); 3) and during RFS, the maximum arch angle of the INT group declined significantly by 5.1% (p < 0.001, Cohen's d = 1.49), the arch height at touchdown increased significantly in the INT group by 32.1% (p < 0.001, Cohen's d = 1.98). Conclusion: The 12-week gait retraining program combined with foot core exercise improved the arch in both static and dynamic positions with a moderate to large effect size, demonstrating the superiority of this combined intervention over the standalone interventions. Thus, runners with weak arch muscles are encouraged to use this combined intervention as an approach to enhance the arch.

Reversing the Mismatch With Forefoot Striking to Reduce Running Injuries

Recent studies have suggested that 95% of modern runners land with a rearfoot strike (RFS) pattern. However, we hypothesize that running with an RFS pattern is indicative of an evolutionary mismatch that can lead to musculoskeletal injury. This perspective is predicated on the notion that our ancestors evolved to run barefoot and primarily with a forefoot strike (FFS) pattern. We contend that structures of the foot and ankle are optimized for forefoot striking which likely led to this pattern in our barefoot state. We propose that the evolutionary mismatch today has been driven by modern footwear that has altered our footstrike pattern. In this paper, we review the differences in foot and ankle function during both a RFS and FFS running pattern. This is followed by a discussion of the interaction of footstrike and footwear on running mechanics. We present evidence supporting the benefits of forefoot striking with respect to common running injuries such as anterior compartment syndrome and patellofemoral pain syndrome. We review the importance of a gradual shift to FFS running to reduce transition-related injuries. In sum, we will make an evidence-based argument for the use of minimal footwear with a FFS pattern to optimize foot strength and function, minimize ground reaction force impacts and reduce injury risk.

The Coupling of Stride Length and Foot Strike in Running

Modifying stride length and/or foot strike in running results in mechanical alterations associated with injury risk. Stride length and foot strike have often been treated as independent factors that affect running mechanics, but there is evidence to suggest that they may be coupled. The purpose of this study was to determine if foot strike and stride length are coupled in running, and if so, can these variables be independently manipulated? Additionally, we sought to determine how independently and simultaneously manipulating stride length and foot strike influenced running kinematics and kinetics. Fifteen individuals ran over ground with stride lengths +/– 10 % of their preferred stride length while adopting both a fore/mid foot strike and rear foot strike pattern, as well as running with their self-selected stride length and foot strike when the opposite variable was controlled. Three-dimensional motion capture and force plate data were captured synchronously during the manipulated stride length x foot strike trials. The results indicate that foot strike and stride length are coupled, with shorter stride lengths being associated with a F/MFS and longer stride lengths being associated with a RFS pattern. Impact peak magnitude was primarily dependent on foot strike, with a F/MFS pattern reducing the magnitude of the impact peak force regardless of stride length. Peak vertical and horizontal ground reaction forces were found to be primarily dependent on stride length, with longer stride lengths resulting in increased vertical and horizontal ground reaction forces, regardless of foot strike. It is difficult, but possible, to independently manipulate stride length and foot strike. Clinicians should be aware of the coupled changes in stride length and foot strike.

An Identical Twin Study on Human Achilles Tendon Adaptation: Regular Recreational Exercise at Comparatively Low Intensities Can Increase Tendon Stiffness

Achilles tendon adaptation is a key aspect of exercise performance and injury risk prevention. However, much debate exists about the adaptation of the Achilles tendon in response to exercise activities. Most published research is currently limited to elite athletes and selected exercise activities. Also, existing studies on tendon adaptation do not control for genetic variation. Our explorative cross-sectional study investigated the effects of regular recreational exercise activities on Achilles tendon mechanical properties in 40 identical twin pairs. Using a handheld oscillation device to determine Achilles tendon mechanical properties, we found that the Achilles tendon appears to adapt to regular recreational exercise at comparatively low intensities by increasing its stiffness. Active twins showed a 28% greater Achilles tendon stiffness than their inactive twin (p < 0.05). Further, our research extends existing ideas on sport-specific adaptation by showing that tendon stiffness seemed to respond more to exercise activities that included an aerial phase such as running and jumping. Interestingly, the comparison of twin pairs revealed a high variation of Achilles tendon stiffness (305.4–889.8 N/m), and tendon adaptation was only revealed when we controlled for genetic variance. Those results offer new insights into the impact of genetic variation on individual Achilles tendon stiffness, which should be addressed more closely in future studies.

Effects of 12-week transition training with minimalist shoes on Achilles tendon loading in habitual rearfoot strike runners

Minimalist shod runners have reported greater material and mechanical properties of the Achilles tendon (AT) due to increased loading than runners who wear more cushioned running shoes. This study aimed to investigate the effects of 12-week transition training from conventional shoes to minimalist shoes on AT loading in habitual rearfoot strike runners. Seventeen healthy male habitual rearfoot strikers completed 12-week transition training. They were instructed either to run in minimalist shoes with a forefoot strike pattern (MIN + FFS, n = 9) or run in minimalist shoes but were free to develop their strike pattern (MIN, n = 8). Ultrasound images were captured to determine the cross-sectional area of the AT. Sagittal plane ankle kinematics and ground reaction forces were recorded simultaneously to quantify ankle joint mechanics and AT loading. The strike angle significantly decreased in MIN + FFS after the transition training, indicating a flatter foot at initial contact, whereas no changes were observed in MIN. After training, a significant increase in peak plantarflexion moment was observed for MIN + FFS (15.4%) and MIN (7.6%). Significantly increased peak AT force, peak loading rate and peak stress were observed after training in both groups. Specifically, MIN + FFS had a greater increase in peak AT force (20.3% versus 10.1%), peak loading rate (37.2% versus 25.4%) and peak AT stress (13.7% versus 8.1%) than MIN. Furthermore, for both groups, there were no significant differences in the moment arm and cross-sectional area of the AT observed before and after 12 weeks of training. The results of this study suggested that it was insufficient to promote the morphological adaptation of the AT, but the mechanical loading of the AT was adapted during running after 12-week transition training with minimalist shoes in MIN + FFS and MIN. Preliminary evidence showed that a gradual transition to minimalist shoes with a forefoot strike pattern may be beneficial to the mechanical loading of the AT.

Backward Running on a Negative Slope as a Treatment for Achilles Tendinopathy in Runners: A Feasibility Pilot Study

CONTEXT

Achilles tendinopathy (AT) is a common musculoskeletal injury among runners. Eccentric exercises are considered first-line treatment. However, during the early stages of rehabilitation, patients are usually instructed to stop running. Backward running (BR) on a negative slope provides a similar eccentric load while enabling ongoing physical activity; thus, it may be suggested as an alternative treatment.

OBJECTIVES

To determine the feasibility of a BR program as a treatment option for AT in runners.

DESIGN

Prospective, single-arm feasibility study.

SETTING

Outpatient clinic.

PATIENTS

Recreational runners diagnosed with AT and referred to the Meuhedet Health Services Physical Therapy Clinic in Jerusalem, Israel, from September 2019 to February 2020.

INTERVENTION

The patients completed a 5-week (9 sessions) rehabilitation program of supervised BR on a negatively inclined treadmill.

MAIN OUTCOME MEASURES

Compliance with the program was evaluated by calculating the percentage of patients who completed the full protocol with no adverse events. Personal running-related goals were set before the program and were assessed following rehabilitation using the goal attainment scaling method. Forward-running time until the onset of relevant Achilles tendon pain, and the Victorian Institute of Sports Assessment Scale-Achilles were measured at baseline (T0), before treatment session 6 (T1), and after the last session (T2).

RESULTS

Among the 15 patients recruited, 14 (93%), average age 48.8 (10.4) years (86% males), completed the full protocol with no adverse events. Almost all participants (85.7%) achieved their running-related functional goals. Postintervention, the median forward-running time increased from 52.5 (92.5) to 900 (522.5) seconds (P = .008, effect size = .858), and the median Victorian Institute of Sports Assessment Scale-Achilles score improved by 28 points (P = .003, effect size = .881).

CONCLUSIONS

BR on a negative slope may be a feasible treatment method for runners suffering from AT. Future randomized control trials are required to further validate the efficacy of this method.

Sex Differences in the Morphological and Mechanical Properties of the Achilles Tendon

Background: Patients with Achilles tendon (AT) injuries are often engaged in sedentary work because of decreasing tendon vascularisation. Furthermore, men are more likely to be exposed to AT tendinosis or ruptures. These conditions are related to the morphological and mechanical properties of AT, but the mechanism remains unclear. This study aimed to investigate the effects of sex on the morphological and mechanical properties of the AT in inactive individuals. Methods: In total, 30 inactive healthy participants (15 male participants and 15 female participants) were recruited. The AT morphological properties (cross-sectional area, thickness, and length) were captured by using an ultrasound device. The AT force–elongation characteristics were determined during isometric plantarflexion with the ultrasonic videos. The AT stiffness was determined at 50%–100% maximum voluntary contraction force. The AT strain, stress, and hysteresis were calculated. Results: Male participants had 15% longer AT length, 31% larger AT cross-sectional area and 21% thicker AT than female participants (p < 0.05). The plantarflexion torque, peak AT force, peak AT stress, and AT stiffness were significantly greater in male participants than in female participants (p < 0.05). However, no significant sex-specific differences were observed in peak AT strain and hysteresis (p > 0.05). Conclusions: In physically inactive adults, the morphological properties of AT were superior in men but were exposed to higher stress conditions. Moreover, no significant sex-specific differences were observed in peak AT strain and hysteresis, indicating that the AT of males did not store and return elastic energy more efficiently than that of females. Thus, the mechanical properties of the AT should be maintained and/or improved through physical exercise.

Relationship between Connective Tissue Morphology and Lower-Limb Stiffness in Endurance Runners. A Prospective Study

BACKGROUND

The lower limb behaves like a spring compressing and decompressing during running, where lower-limb stiffness is one of the most influential factors. This prospective observational study is aimed at examining the relationship between the connective tissue morphology and lower-limb stiffness and investigating whether the barefoot/shod condition influences on such relationship.

METHODS

14 male amateur runners (10-km time trial <50') were included. Data were recorded over one session, where participants ran 2 trials (i.e., barefoot and shod conditions) of 3 minutes at 12 km/h, where running spatiotemporal parameters and vertical (Kvert) and leg stiffness (Kleg) were obtained. Prior to testing trials, thickness and cross-sectional area (CSA) were recorded for Achilles (AT) and patellar tendons (PT) and plantar fascia (PF) with ultrasound.

RESULTS

Under barefoot condition, a positive correlation was found between Kleg and AT-thickness and CSA and PF-thickness; and between Kvert and AT-thickness and PF thickness. Under shod condition, a positive correlation was found between Kleg and PT-CSA and PT-thickness, and between Kvert and PT-CSA and PT-thickness.

CONCLUSIONS

The results reveal a specificity of the relationship between the lower-limb stiffness and the morphology of the connective tissue. Greater tendon shows higher lower-limb stiffness when that tendon is specially demanded by the function.

What are the Benefits and Risks Associated with Changing Foot Strike Pattern During Running? A Systematic Review and Meta-analysis of Injury, Running Economy, and Biomechanics

BACKGROUND

Running participation continues to increase. The ideal strike pattern during running is a controversial topic. Many coaches and therapists promote non-rearfoot strike (NRFS) running with a belief that it can treat and prevent injury, and improve running economy.

OBJECTIVE

The aims of this review were to synthesise the evidence comparing NRFS with rearfoot strike (RFS) running patterns in relation to injury and running economy (primary aim), and biomechanics (secondary aim).

DESIGN

Systematic review and meta-analysis. Consideration was given to within participant, between participant, retrospective, and prospective study designs.

DATA SOURCES

MEDLINE, EMBASE, CINAHL, and SPORTDiscus.

RESULTS

Fifty-three studies were included. Limited evidence indicated that NRFS running is retrospectively associated with lower reported rates of mild (standard mean difference (SMD), 95% CI 3.25, 2.37-4.12), moderate (3.65, 2.71-4.59) and severe (0.93, 0.32-1.55) repetitive stress injury. Studies prospectively comparing injury risk between strike patterns are lacking. Limited evidence indicated that running economy did not differ between habitual RFS and habitual NRFS runners at slow (10.8-11.0 km/h), moderate (12.6-13.5 km/h), and fast (14.0-15.0 km/h) speeds, and was reduced in the immediate term when an NRFS-running pattern was imposed on habitual RFS runners at slow (10.8 km/h; SMD = - 1.67, - 2.82 to - 0.52) and moderate (12.6 km/h; - 1.26, - 2.42 to - 0.10) speeds. Key biomechanical findings, consistently including both comparison between habitual strike patterns and following immediate transition from RFS to NRFS running, indicated that NRFS running was associated with lower average and peak vertical loading rate (limited-moderate evidence; SMDs = 0.72-2.15); lower knee flexion range of motion (moderate-strong evidence; SMDs = 0.76-0.88); reduced patellofemoral joint stress (limited evidence; SMDs = 0.63-0.68); and greater peak internal ankle plantar flexor moment (limited evidence; SMDs = 0.73-1.33).

CONCLUSION

The relationship between strike pattern and injury risk could not be determined, as current evidence is limited to retrospective findings. Considering the lack of evidence to support any improvements in running economy, combined with the associated shift in loading profile (i.e., greater ankle and plantarflexor loading) found in this review, changing strike pattern cannot be recommended for an uninjured RFS runner.

PROSPERO REGISTRATION

CRD42015024523.

Leg Stiffness and Vertical Stiffness of Habitual Forefoot and Rearfoot Strikers during Running

Foot strike patterns influence the running efficiency and may be an injury risk. However, differences in the leg stiffness between runners with habitual forefoot (hFFS) and habitual rearfoot (hRFS) strike patterns remain unclear. This study aimed at determining the differences in the stiffness, associated loading rate, and kinematic performance between runners with hFFS and hRFS during running. Kinematic and kinetic data were collected amongst 39 runners with hFFS and 39 runners with hRFS running at speed of 3.3 m/s, leg stiffness (Kleg), and vertical stiffness (Kvert), and impact loads were calculated. Results found that runners with hFFS had greater Kleg (P = 0.010, Cohen′s d = 0.60), greater peak vertical ground reaction force (vGRF) (P = 0.040, Cohen′s d = 0.47), shorter contact time(t_c) (P < 0.001, Cohen′s d = 0.85), and smaller maximum leg compression (ΔL ) (P = 0.002, Cohen′s d = 0.72) compared with their hRFS counterparts. Runners with hFFS had lower impact peak (IP) (P < 0.001, Cohen′s d = 1.65), vertical average loading rate (VALR) (P < 0.001, Cohen′s d = 1.20), and vertical instantaneous loading rate (VILR) (P < 0.001, Cohen′s d = 1.14) compared with runners with hRFS. Runners with hFFS landed with a plantar flexed ankle, whereas runners with hRFS landed with a dorsiflexed ankle (P < 0.001, Cohen′s d = 3.35). Runners with hFFS also exhibited more flexed hip (P = 0.020, Cohen′s d = 0.61) and knee (P < 0.001, Cohen′s d = 1.15) than runners with hRFS at initial contact. These results might indicate that runners with hFFS were associated with better running economy through the transmission of elastic energy.

Acute shoe effects on Achilles tendon loading in runners with habitual rearfoot strike pattern

OBJECTIVES

Although the overuse injury rate of the Achilles tendon (AT) for running is high, the effect of shoe conditions on AT loading remains unclear. Hence, this study aims to determine the mechanical properties of AT during running under different shoe conditions (minimalist vs. conventional shoes).

DESIGN

This work is a controlled laboratory study.

METHODS

Sixteen healthy male rearfoot strike runners were recruited to complete over ground running trials at 3.33 m/s (±5%) under two shoe conditions (minimalist shoes: INOV-8 Bare-XF 210; conventional shoes: NIKE AIR ZOOM PEGASUS 34). Sagittal plane ankle kinematics and ground reaction forces were simultaneously recorded. Ankle joint mechanics (ankle joint angle and moment) and the mechanical properties (peak force, impulse, stress, strain, and their corresponding peak rate) of the AT were calculated.

RESULTS

In comparison with conventional shoes, wearing minimalist shoes showed significant changes (p < 0.05): (1) decreased strike angle (48.92 ± 9.01 vs. 41.04 ± 8.69°); (2) increased ankle moment (2.34 ± 0.44 vs. 2.55 ± 0.46 Nm/kg); (3) increased peak AT force (5.85 ± 1.22 vs. 6.24 ± 1.13 BW), AT force impulse (0.65 ± 0.13 vs. 0.70 ± 0.13 BW·s), peak AT loading rate (109.94 ± 9.33 vs. 118.84 ± 26.62 BW/s), and average loading rate (48.42 ± 15.64 vs. 54.90 ± 17.47 BW/s); (4) decreased time to peak AT force (126.31 ± 20.68 vs. 117.77 ± 17.62 ms); (5) increased AT stress (66.96 ± 14.59 vs. 71.89 ± 14.74 MPa), strain (8.19 ± 1.77 vs. 8.78 ± 1.80 %), peak AT stress rate (66.96 ± 14.59 vs. 71.89 ± 14.74 MPa/s), and strain rate (148.71 ± 48.52 vs. 167.28 ± 42.82 %/s).

CONCLUSION

Increased AT force, loading rate, and stress were observed in runners who habitually wear conventional shoes with rearfoot strike patterns when they wore minimalist shoes. Hence, we recommend a gradual transition to minimalist shoes for runners who habitually wear conventional shoes with rearfoot strike patterns.

Changes in the Plantar Flexion Torque of the Ankle and in the Morphological Characteristics and Mechanical Properties of the Achilles Tendon after 12-Week Gait Retraining

Purpose: Although the Achilles tendon (AT) is the largest and strongest tendon, it remains one of the most vulnerable tendons among elite and recreational runners. The present study aims to explore the effects of 12-week gait retraining (GR) on the plantar flexion torque of the ankle and the morphological and mechanical properties of the AT. Methods: Thirty-four healthy male recreational runners (habitual rearfoot strikers) who never tried to run in minimal shoes were recruited, and the intervention was completed (20 in the GR group vs. 14 in the control (CON) group). The participants in the GR group were asked to run in minimal shoes (INOV-8 BARE-XF 210) provided by the investigators with forefoot strike patterns during the progressive 12-week GR. Meanwhile, the participants in the CON group were instructed to run in their own running shoes, which they were familiar with, with original foot strike patterns and intensities. The morphological properties of the AT, namely, length and cross-sectional area (CSA), were obtained by using an ultrasound device. A dynamometer was utilized simultaneously to measure and calculate the plantar flexion torque of the ankle, the rate of torque development, the peak force of the AT, and the stress and strain of the AT. Results: After 12-week GR, the following results were obtained: (1) A significant time effect in the peak ankle plantarflexion torque was observed (p = 0.005), showing a 27.5% increase in the GR group; (2) A significant group effect in the CSA was observed (p = 0.027), specifically, the increase in CSA was significantly larger in the GR group than the CON group; (3) A significant time effect in the peak AT force was observed (p = 0.005), showing a 27.5% increase in the GR group. Conclusion: The effect of 12 weeks of GR is an increase in AT CSA, plantar flexor muscle strength of the ankle, and peak AT force during a maximal voluntary isometric contraction test. These changes in AT morphology and function could be positive for tendon health and could prevent future AT injury.

Effects of Foot Strike Techniques on Running Biomechanics: A Systematic Review and Meta-analysis

CONTENT

Distance running is one of the most popular physical activities, and running-related injuries (RRIs) are also common. Foot strike patterns have been suggested to affect biomechanical variables related to RRI risks.

OBJECTIVE

To determine the effects of foot strike techniques on running biomechanics.

DATA SOURCES

The databases of Web of Science, PubMed, EMBASE, and EBSCO were searched from database inception through November 2018.

STUDY SELECTION

The initial electronic search found 723 studies. Of these, 26 studies with a total of 472 participants were eligible for inclusion in this meta-analysis.

STUDY DESIGN

Systematic review and meta-analysis.

LEVEL OF EVIDENCE

Level 4.

DATA EXTRACTION

Means, standard deviations, and sample sizes were extracted from the eligible studies, and the standard mean differences (SMDs) were obtained for biomechanical variables between forefoot strike (FFS) and rearfoot strike (RFS) groups using a random-effects model.

RESULTS

FFS showed significantly smaller magnitude (SMD, -1.84; 95% CI, -2.29 to -1.38; P < 0.001) and loading rate (mean: SMD, -2.1; 95% CI, -3.18 to -1.01; P < 0.001; peak: SMD, -1.77; 95% CI, -2.21 to -1.33; P < 0.001) of impact force, ankle stiffness (SMD, -1.69; 95% CI, -2.46 to -0.92; P < 0.001), knee extension moment (SMD, -0.64; 95% CI, -0.98 to -0.3; P < 0.001), knee eccentric power (SMD, -2.03; 95% CI, -2.51 to -1.54; P < 0.001), knee negative work (SMD, -1.56; 95% CI, -2.11 to -1.00; P < 0.001), and patellofemoral joint stress (peak: SMD, -0.71; 95% CI, -1.28 to -0.14; P = 0.01; integral: SMD, -0.63; 95% CI, -1.11 to -0.15; P = 0.01) compared with RFS. However, FFS significantly increased ankle plantarflexion moment (SMD, 1.31; 95% CI, 0.66 to 1.96; P < 0.001), eccentric power (SMD, 1.63; 95% CI, 1.18 to 2.08;P < 0.001), negative work (SMD, 2.60; 95% CI, 1.02 to 4.18; P = 0.001), and axial contact force (SMD, 1.26; 95% CI, 0.93 to 1.6; P < 0.001) compared with RFS.

CONCLUSION

Running with RFS imposed higher biomechanical loads on overall ground impact and knee and patellofemoral joints, whereas FFS imposed higher biomechanical loads on the ankle joint and Achilles tendon. The modification of strike techniques may affect the specific biomechanical loads experienced on relevant structures or tissues during running.

Short-term effects of a trunk modification program on patellofemoral joint stress in asymptomatic runners

OBJECTIVES

To evaluate short-term effects of a four-week gait retraining program using visual feedback on trunk flexion angle, patellofemoral joint (PFJ) stress, lower extremity biomechanics and motor skill automaticity.

DESIGN

Longitudinal interventional study.

SETTINGS

University research laboratory.

PARTICIPANTS

Twelve asymptomatic recreational runners (seven male and five female).

MAIN OUTCOME MEASURES

Trunk kinematics as well as lower extremity kinematics and kinetics were assessed prior to training at week 1 (baseline) and week 2, 3, 4 and 8 (retention). PFJ stress was computed using a sagittal plane model. A dual-task procedure was performed to examine automaticity.

RESULTS

At week 8, runners demonstrated 10.1° increase in trunk flexion angle (p < .001) and 17.8% reduction in peak PFJ stress (p < .001) compared to baseline. This is associated with a 16.8% decrease in knee extensor moment and less than 2.5° change in knee flexion angle. Participants also showed 33.3% increase in peak hip extensor moment and small reduction in peak ankle plantar flexor moment. Lastly, runners demonstrated automaticity of the modified skill with a dual-task cost of less than 3%.

CONCLUSION

The gait retraining program is effective to elicit short term changes in trunk position, PFJ stress, and automaticity of the new motor skill.

Footwear and footstrike change loading patterns in running

Loading rates have been linked to running injuries, revealing persistent impact features that change direction among three-dimensional axes in different footwear and footstrike patterns. Extracting peak loads from ground reaction forces, however, can neglect the time-varying loading patterns experienced by the runner in each footfall. Following footwear and footstrike manipulations during laboratory-based overground running, we examined three-dimensional loading rate-time features in each direction (X, Y, Z) using principal component analysis. Twenty participants (9 M, 11 F, age: 25.3 ± 3.6 y) were analysed during 14 running trials in each of two footwear (cushioned and minimalist) and three footstrike conditions (forefoot, midfoot, rearfoot). Two principal components (PC) captured the primary loading rate-time features (PC1: 42.5% and PC2: 22.8% explained variance) and revealed interaction among axes, footwear, and footstrike conditions (PC1: F _{(2.1, 40.1)} = 5.6, p = 0.007, η ² = 0.23; PC2: F _{(2.0, 38.4)} = 62.3, p < 0.001, η ² = 0.77). Rearfoot running in cushioned footwear attenuated impact loads in the vertical direction, and forefoot running in minimalist footwear attenuated impact loads in the anterior-posterior and medial-lateral directions relative to forefoot running in cushioned shoes. Loading patterns depend on footwear and footstrike interactions, which require shoes that match the runner's footstrike pattern.

Twelve-Week Gait Retraining Reduced Patellofemoral Joint Stress during Running in Male Recreational Runners

Purpose

To explore the changes in knee sagittal angle and moment and patellofemoral joint (PFJ) force and stress before and after 12-week gait retraining.

Methods

A total of 30 healthy male recreational runners were randomized into a control group (n = 15) who ran in their original strike pattern using minimalist shoes or experimental group (n = 15) who ran in a forefoot strike pattern using minimalist shoes during the 12-week gait retraining. The kinematic and kinetic data of the dominant leg of the participants during the 12 km/h running were collected by 3D motion capture systems and 3D force platforms. Besides, the biomechanical property of the PFJ was calculated on the basis of the joint force model and the regression equation of the contact area.

Results

After the 12-week gait retraining, 78% of the rearfoot strikers turned into forefoot strikers. Peak knee extension moment and peak PFJ stress decreased by 13.8% and 13.3% without altering the running speed, respectively. Meanwhile, no changes in maximum knee flexion angle/extension moment and PFJ force/stress were observed for the control group.

Conclusion

The 12-week gait retraining effectively reduced the PFJ stress, thereby providing a potential means of reducing the risk of patellofemoral pain syndrome while running.

Foot strike pattern during running alters muscle-tendon dynamics of the gastrocnemius and the soleus

Running is thought to be an efficient gait due, in part, to the behavior of the plantar flexor muscles and elastic energy storage in the Achilles tendon. Although plantar flexor muscle mechanics and Achilles tendon energy storage have been explored during rearfoot striking, they have not been fully characterized during forefoot striking. This study examined how plantar flexor muscle-tendon mechanics during running differs between rearfoot and forefoot striking. We used musculoskeletal simulations, driven by joint angles and electromyography recorded from runners using both rearfoot and forefoot striking running patterns, to characterize plantar flexor muscle-tendon mechanics. The simulations revealed that foot strike pattern affected the soleus and gastrocnemius differently. For the soleus, forefoot striking decreased tendon energy storage and fiber work done while the muscle fibers were shortening compared to rearfoot striking. For the gastrocnemius, forefoot striking increased muscle activation and fiber work done while the muscle fibers were lengthening compared to rearfoot striking. These changes in gastrocnemius mechanics suggest that runners planning to convert to forefoot striking might benefit from a progressive eccentric gastrocnemius strengthening program to avoid injury.

The effects of midfoot strike gait retraining on impact loading and joint stiffness

OBJECTIVE

To assess the biomechanical changes following a systematic gait retraining to modify footstrike patterns from rearfoot strike (RFS) to midfoot strike (MFS).

DESIGN

Pre-post interventional study. All participants underwent a gait retraining program designed to modify footstrike pattern to MFS.

SETTING

Research laboratory.

PARTICIPANTS

Twenty habitual RFS male runners participated.

MAIN OUTCOME MEASURES

Gait evaluations were conducted before and after the training. Footstrike pattern, vertical loading rates, ankle and knee joint stiffness were compared.

RESULTS

Participants' footstrike angle was reduced (p < 0.001, Cohen's d = 1.65) and knee joint stiffness was increased (p = 0.003, Cohen's d = 0.69). No significant difference was found in the vertical loading rates (p > 0.155). Further subgroup analyses were conducted on the respondents (n = 8, 40% of participants) who exhibited MFS for over 80% of their footfalls during the post-training evaluation. Apart from the increased knee joint stiffness (p = 0.005, Cohen's d = 1.14), respondents exhibited a significant reduction in the ankle joint stiffness (p = 0.019, Cohen's d = 1.17) when running with MFS.

CONCLUSIONS

Gait retraining to promote MFS was effective in reducing runners' footstrike angle, but only 40% of participants responded to this training program. The inconsistent training effect on impact loading suggests a need to develop new training protocols in an effort to prevent running injuries.

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.

Do habitual foot-strike patterns in running influence functional Achilles tendon properties during gait?

The capacity of foot-strike running patterns to influence the functional properties of the Achilles tendon is controversial. This study used transmission-mode ultrasound to investigate the influence of habitual running foot-strike pattern on Achilles tendon properties during barefoot walking and running. Fifteen runners with rearfoot (RFS) and 10 with a forefoot (FFS) foot-strike running pattern had ultrasound transmission velocity measured in the right Achilles tendon during barefoot walking (≈1.1 ms^-1) and running (≈2.0 ms^-1). Temporospatial gait parameters, ankle kinematics and vertical ground reaction force were simultaneously recorded. Statistical comparisons between foot-strike patterns were made using repeated measure ANOVAs. FFS was characterised by a significantly shorter stance duration (-4%), greater ankle dorsiflexion (+2°), and higher peak vertical ground reaction force (+20% bodyweight) than RFS running (P < .05). Both groups adopted a RFS pattern during walking, with only the relative timing of peak dorsiflexion (3%), ground reaction force (1-2%) and peak vertical force loading rates (22-23%) differing between groups (P < .05). Peak ultrasound transmission velocity in the Achilles tendon was significantly higher in FFS during walking (≈100 ms^-1) and running (≈130 ms^-1) than RFS (P < .05). Functional Achilles tendon properties differ with habitual footfall patterns in recreational runners.

Vertical ground reaction forces during gait in children with and without calcaneal apophysitis

BACKGROUND

Heightened vertical load beneath the foot has been anecdotally implicated in the development of activity-related heel pain of the calcaneal apophysis in children but is supported by limited evidence.

RESEARCH QUESTION

This study investigated whether vertical loading patterns during walking and running differed in children with and without calcaneal apophysitis.

METHODS

Vertical ground reaction force, peak plantar pressure (forefoot, midfoot, heel) and temporospatial gait parameters (cadence, step length, stride, stance and swing phase durations) were determined in children with (n = 14) and without (n = 14) calcaneal apophysitis. Measures were acquired during barefoot walking and running at matched and self-selected speed using an instrumented treadmill, sampling at 120 Hz. Statistical comparisons between groups were made using repeated measure ANOVAs.

RESULTS

There were no significant between group differences in vertical ground reaction force peaks or regional peak plantar pressures. However, when normalised to stature, cadence was significantly higher (≈ 5%) and step length shorter (≈ 5%) in children with calcaneal apophysitis than those without, but only during running (P <.05). Maximum pressure beneath the rearfoot during running was significantly correlated with self-reported pain in children with calcaneal apophysitis.

SIGNIFICANCE

Peak vertical force and plantar pressures did not differ significantly in children with and without calcaneal apophysitis during walking or running. However, children with calcaneal apophysitis adopted a higher cadence than children without heel pain during running. While the findings suggest that children with calcaneal apophysitis may alter their cadence to lower pressure beneath the heel and, hence pain, they also highlight the benefit of evaluating running rather than walking gait in children with calcaneal apophysitis.

Effect of habitual foot-strike pattern on the gastrocnemius medialis muscle-tendon interaction and muscle force production during running

The interaction between gastrocnemius medialis (GM) muscle and Achilles tendon, i.e., muscle-tendon unit (MTU) interaction, plays an important role in minimizing the metabolic cost of running. Foot-strike pattern (FSP) has been suggested to alter MTU interaction and subsequently the metabolic cost of running. However, metabolic data from experimental studies on FSP are inconsistent, and a comparison of MTU interaction between FSP is still lacking. We, therefore, investigated the effect of habitual rearfoot and mid-/forefoot striking on MTU interaction, ankle joint work, and plantar flexor muscle force production while running at 10 and 14 km/h. GM muscle fascicles of 9 rearfoot and 10 mid-/forefoot strikers were tracked using dynamic ultrasonography during treadmill running. We collected kinetic and kinematic data and used musculoskeletal models to determine joint angles and calculate MTU lengths. In addition, we used dynamic optimization to assess plantar flexor muscle forces. During ground contact, GM fascicle shortening ( P = 0.02) and average contraction velocity ( P = 0.01) were 40-45% greater in rearfoot strikers than mid-/forefoot strikers. Differences in contraction velocity were especially prominent during early ground contact. Moreover, GM ( P = 0.02) muscle force was greater during early ground contact in mid-/forefoot strikers than rearfoot strikers. Interestingly, we did not find differences in stretch or recoil of the series elastic element between FSP. Our results suggest that, for the GM, the reduced muscle energy cost associated with lower fascicle contraction velocity in mid-/forefoot strikers may be counteracted by greater muscle forces during early ground contact. NEW & NOTEWORTHY Kinetic and kinematic differences between foot-strike patterns during running imply (not previously reported) altered muscle-tendon interaction. Here, we studied muscle-tendon interaction using ultrasonography. We found greater fascicle contraction velocities and lower muscle forces in rearfoot compared with mid-/forefoot strikers. Our results suggest that the higher metabolic energy demand due to greater fascicle contraction velocities might offset the lower metabolic energy demand due to lower muscle forces in rearfoot compared with mid-/forefoot strikers.

The effects of habitual foot strike patterns on Achilles tendon loading in female runners

BACKGROUND

Female runners that habitually use a forefoot/midfoot strike pattern (non-rearfoot runners) may be at greater risk for Achilles tendinopathy compared to runners that habitually use a rearfoot strike pattern. Differences in Achilles tendon loading between non-rearfoot and rearfoot strike runners may be a contributing factor.

RESEARCH QUESTION

Our purpose was to determine if there were differences in Achilles tendon loading and cross-sectional area between female habitual rearfoot and non-rearfoot strike runners.

METHODS

Thirty-five female runners participated in this cross-sectional study (17 rearfoot strike runners, 18 non-rearfoot strike runners). Ultrasound images of the Achilles tendon were used to measure cross-sectional area. Kinematic and kinetic data were collected at a set running speed and used in a muscloskeletal model to calculate Achilles tendon force. Achilles tendon stress was determined from specific Achilles tendon cross-sectional area. Principal components (PC) analysis was performed to identify/characterize the primary sources of variability in the Achilles tendon stress time series. The PC scores and cross-sectional area where compared using independent t-tests.

RESULTS

PC 1 reflected variability in the Achilles tendon stress magnitude from 25 to 100% of stance, PC 2 reflected timing variability, and PC 3 reflected variability in the magnitude during early stance (0-25%). The non-rearfoot strike runners demonstrated higher PC scores for PC 1 and PC 3 compared to the rearfoot strike runners. This reflected greater Achilles tendon stress during mid/late stance (PC 1) and early stance (PC 3) for the non-rearfoot strike runners. For PC 2, there was a trend toward higher PC scores in the non-rearfoot strike runners. Achilles tendon cross-sectional area for the rearfoot and non-rearfoot strike runners were not different.

SIGNIFICANCE

Habitual non-rearfoot strike runners did not have greater cross-sectional area despite higher Achilles tendon loading, which may pose a higher risk for Achilles tendinopathy.

The effects & mechanisms of increasing running step rate: A feasibility study in a mixed-sex group of runners with patellofemoral pain

OBJECTIVES

To explore feasibility of recruitment and retention of runners with patellofemoral pain (PFP), before delivering a step rate intervention.

DESIGN

Feasibility study.

SETTING

Human performance laboratory.

PARTICIPANTS

A mixed-sex sample of runners with PFP (n = 11).

MAIN OUTCOME MEASURES

Average/worst pain and the Kujala Scale were recorded pre/post intervention, alongside lower limb kinematics and surface electromyography (sEMG), sampled during a 3 KM treadmill run.

RESULTS

Recruitment and retention of a mixed-sex cohort was successful, losing one participant to public healthcare and with kinematic and sEMG data lost from single participants only. Clinically meaningful reductions in average (MD = 2.1, d = 1.7) and worst pain (MD = 3.9, d = 2.0) were observed. Reductions in both peak knee flexion (MD = 3.7°, d = 0.78) and peak hip internal rotation (MD = 5.1°, d = 0.96) were observed, which may provide some mechanistic explanation for the identified effects. An increase in both mean amplitude (d = 0.53) and integral (d = 0.58) were observed for the Vastus Medialis Obliqus (VMO) muscle only, of questionable clinical relevance.

CONCLUSIONS

Recruitment and retention of a mixed sex PFP cohort to a step rate intervention involving detailed biomechanical measures is feasible. There are indications of both likely efficacy and associated mechanisms. Future studies comparing the efficacy of different running retraining approaches are warranted.