Cushioned Shoes Research Articles

Plantar Flexor Muscle Activity and Fascicle Behavior in Gastrocnemius Medialis During Running in Highly Cushioned Shoes With Carbon-Fiber Plates.

The purposes of this study were to clarify the electromyography (EMG) of plantar flexors and to analyze the fascicle and tendon behaviors of the gastrocnemius medialis (GM) during running in the carbon-fiber plate embedded in thicker midsole racing shoes, such as the Nike ZoomX Vaporfly (VF) and traditional racing shoes (TRAD). We compared the fascicle and series elastic element behavior of the GM and EMG of the lower limb muscles during running (14km/h, 45s) in athletes wearing VF or TRAD. GM EMGs in the push-off phase were approximately 50% lower in athletes wearing VF than in TRAD. Although the series elastic element behavior and/or mean fascicle-shortening velocity during the entire stance phase were not significantly different between VF and TRAD, a significant difference was found in both the mean EMG and integral EMG of the GM during the push-off phase. EMG of the gastrocnemius lateralis (GL) during the first half of the push-off phase was significantly different between VF and TRAD. Present results suggest that VF facilitates running propulsion, resulting in a decrease in GM and GL EMGs at a given running velocity during the push-off phase, leading to a reduction in metabolic cost.

Quantifying coordinative patterns in steady‐state running: The impact of footwear and foot strike on joint coupling variability

AbstractIn this study, we aimed to compare and contrast the intralimb coordinative patterns of habitual forefoot strikers (FFS) and rearfoot strikers (RFS) during steady‐state running across three different shoe types: minimalist, neutral and cushioned shoes. To describe these coordinative patterns, we implemented the concept of the ‘preferred movement path’ which represents the movement path that runners naturally select in response to their physical capacity and external environment. We quantified cycle‐to‐cycle consistency (ACC) and within‐trial variance in coordination patterns (SoV) using joint angle data from the ankle and knee for ankle‐knee coupling and from the knee and hip for knee‐hip coupling. Additionally, we calculated the measure of shape difference in joint coupling as the sum of squared distances (SSD) between/within conditions and groups. The percentage of runners who displayed shape differences below certain SSD thresholds was also evaluated. Our findings revealed no significant group or shoe type effect on any of the variability measures (ACC: p = 0.460 for ankle‐knee and p = 0.832 for knee‐hip; SoV: p = 0.345 for ankle‐knee and p = 0.755 for knee‐hip). However, there was a significant (p < 0.001) shape difference observed between the most extreme shoe conditions. Despite this, when runners switched shoes, 70%–90% of them maintained their original coordinative pattern across both joint couplings, indicating a strong adherence to their preferred movement path. This suggests that while shoe type can influence the shape of the coordinative pattern, the inherent movement tendencies of the runners remain largely consistent.

Effects of a 12-week gait retraining program on the Achilles tendon adaptation of habitually shod runners.

This study investigated the effects of a 12-week gait retraining program on the morphological and mechanical properties of the Achilles tendon (AT) during running on the basis of real-time dynamic ultrasound imaging. A total of 30 male recreational runners who were used to wearing cushioned shoes with a rearfoot strike (RFS) pattern were recruited. They were randomized into a retraining group (RG, n = 15) and a control group (CG, n = 15). The RG group was asked to run in five-fingered minimalist shoes with a forefoot strike (FFS) pattern, and the CG group was asked to keep their strike pattern. Three training sessions were performed per week. All the participants in RG uploaded running tracks obtained through a mobile application (.jpg) after each session for training supervision. The ground reaction force, kinematics, and kinetics of the ankle joint at 10 km/h were collected using an instrumented split-belt treadmill and a motion capture system. The morphological (length and cross-sectional area) and mechanical characteristics (force, stress, strain, etc.) of AT invivo were recorded and calculated with a synchronous ultrasonic imaging instrument before and after the intervention. Repeated two-way ANOVA was used to compare the aforementioned parameters. A total of 28 participants completed the training. The strike angle of RG after training was significantly smaller than that before training and significantly smaller than that of CG after training (F (1, 13) = 23.068, p < 0.001, partial η2 = 0.640). The length (F (1, 13) = 10.086, p = 0.007, partial η2 = 0.437) and CSA (F (1, 13) = 7.475, p = 0.017, partial η2 = 0.365) of AT in RG increased after training. A significant main effect for time was observed for the time-to-peak AT force (F (1, 13) = 5.225, p = 0.040, partial η2 = 0.287), average (F (1, 13) = 7.228, p = 0.019, partial η2 = 0.357), and peak AT loading rate (F (1, 13) = 11.687, p = 0.005, partial η2 = 0.473). Preliminary evidence indicated that a 12-week gait retraining program could exert a beneficial effect on AT. 57% (8/14) runners in RG shifted from RFS to FFS pattern. Although not all runners were categorized as FFS pattern after the intervention, their foot strike angle was reduced. Retraining primarily positively promoted AT morphological properties (i.e., CSA and length) to strengthen AT capability for mechanical loading.

Time and frequency domain analysis of ground reaction force in highly cushioned shoes with a carbon-fiber plate

Time and frequency domain analysis of ground reaction force in highly cushioned shoes with a carbon-fiber plate

Time course of muscle activation, energetics and mechanics of running in minimalist and traditional cushioned shoes during level running

The study aimed to compare the ankle muscles activation, biomechanics and energetics of running in male runners during submaximal level run using minimalist (MinRS) and traditional cushioned (TrdRS) running shoes. During 45-min running in MinRS and TrdRS, the ankle muscles pre- and co-activation, biomechanics, and energetics of running of 16 male endurance runners (25.5 ± 3.5 yr) were assessed using surface electromyography (tibialis anterior and gastrocnemius lateralis), instrumented treadmill and indirect calorimetry, respectively. The net energy cost of running (Cr) was similar for both conditions (P = 0.25) with a significant increase over time (P < 0.0001). Step frequency (P < 0.001), and total mechanical work (P = 0.001) were significantly higher in MinRS than in TrdRS with no evolution over time (P = 0.28 and P = 0.85, respectively). The ankle muscles pre- and co-activation during the contact phase did not differ between the two shoe conditions (P ≥ 0.33) or over time (P ≥ 0.15). In conclusion, during 45-min running, Cr and muscle pre- and co-activation were not significantly different between MinRS and TrdRS with significantly higher step frequency and total mechanical work noted in the former than in the latter. Moreover, Cr significantly increased during the 45-min trial in both shoe conditions along with no significant change over time in muscle activation and biomechanical variables.

Effects of Highly Cushioned and Resilient Racing Shoes on Running Economy at Slower Running Speeds.

The Nike Vaporfly line of running shoes improves running economy by ∼2.7% to 4.2% at running speeds of 13 to 18km·h-1. It is unclear whether similar benefits are conferred at slower speeds. Our purpose was to determine the effects of the Nike ZoomX Vaporfly Next% 2 (VFN2) on running economy at 10 and 12km·h-1 compared with a mass-matched control (CTRL) shoe. Sixteen runners completed 4 × 5-minute trials at both 10 and 12km·h-1 on the same day. Each shoe was tested twice at each speed in a counterbalanced, mirrored sequence. Data are displayed as mean (SD). A 2-way repeated-measures analysis of variance showed a significant shoe × speed interaction for oxygen consumption (P = .021). At 12km·h-1, oxygen consumption (in mL·kg-1·min-1) was lower (-1.4% [1.1%]; P < .001) for VFN2 (35.8 [1.7]) relative to CTRL (36.4 [1.7]). That was greater in magnitude than the differences observed at 10km·h-1 (-0.9% [1.8%]; P = .065) between VFN2 (29.4 [1.9]) and CTRL (29.6 [1.9]). From these data, it appears that the VFN2 still enhances running economy at 10 and 12km·h-1; however, these benefits are smaller in magnitude compared with previous research at faster speeds.

Cushioned Footwear Effect on Pain and Gait Characteristics of Individuals with Knee Osteoarthritis: A Double-Blinded 3 Month Intervention Study.

One of the recommendations for individuals with knee osteoarthritis (OA) is the use of specific footwear, such as sturdy or cushioned shoes. However, the long-term use effects of using cushioned shoes on the pain and spatiotemporal gait parameters in individuals with knee OA are yet to be reported. We therefore aimed to compare the efficacy of cushioned sport footwear versus sham shoes on motor functions, pain and gait characteristics of individuals with knee OA who used the shoes for 3 months. In a double-blinded study, we provided 26 individuals with knee OA with cushioned sport shoes and 12 individuals with knee OA with similar sport shoes without cushioning for 3 months. The gait analysis, the timed up and go (TUG) test and the Western Ontario and McMaster Universities Arthritis Index (WOMAC) were conducted and the pain levels were measured at the baseline, 1 month, and 3 months after the baseline. We found that the cushioned shoes reduce the amount of pain (based on WOMAC) in the affected knee and increase functionality in the research group, but not in the control group. Gait velocity and cadence were increased in both groups. Gait spatiotemporal parameters and their symmetry were unaffected during the intervention. We conclude that the use of cushioned shoes should be recommended to individuals with knee OA for alleviating pain.

Balance effects of tactile stimulation at the foot

Balance relies on several types of sensory information, including somatosensory senses such as touch and position sense (proprioception). As these senses decline in older adults, there is a question of whether shoes limit somatosensory feedback from the floor. Textured insoles are designed to stimulate the soles of the feet to enhance tactile feedback. Textured insoles have shown balance benefits in some populations, but it is unclear if such tactile stimulation improves a person's balance even in cushioned athletic shoes, which dampen proprioceptive signals. Here we ask whether tactile vs. proprioceptive cues contribute differently to balance control in the healthy somatosensory system. We assessed balance in 20 healthy young adults under four footwear conditions: cushioned shoes with regular insoles, cushioned shoes with textured insoles, barefoot, and minimalist shoes. Each condition was evaluated using the Y-Balance Test (YBT) and the Balance Error Scoring System (BESS), validated tests of dynamic and static balance, respectively. YBT is a dynamic reaching test performed on one leg. The BESS includes various stance conditions with eyes closed. The results showed that footwear influenced dynamic balance only, with textured insoles leading to significantly better performance than barefoot and minimalist shoes did in the YBT. These results suggest that at least for dynamic balance, balance benefits of tactile stimulation from the textured insoles offset any dampening of proprioception caused by the athletic shoes' cushioning. Future research on how these conditions compare in older adults may lead to improved footwear recommendations to reduce fall risk and injuries for that population.

The Effect of Maximalist Running Shoes on Impact Loading: A Critically Appraised Topic

Clinical Scenario: Running injuries are common in runners. The use of maximal cushioned shoes (MAX) has been suggested as a preventive measure for reducing impact loading and thus running-related injuries. Clinical Question: Do maximalist running shoes reduce impact loading compared to traditional shoes in runners? Summary of Key Findings: A search was performed for articles exploring MAX on impact loading in runners. Five articles were included in this critically appraised topic. All were case-controlled laboratory studies that compared the MAX to a traditional running shoe. None of the studies found a reduction in impact loading with use of the MAX. Clinical Bottom Line: Based on five case-controlled studies, a MAX does not reduce impact loading on level surfaces or downhill running. Based on mixed results, the MAX may increase impact forces during level and downhill running. Future research should include randomized controlled trials that assess impact forces after the runner has adapted to the MAX and after running ultradistances. Strength of Recommendation: In agreement with the Center of Evidence-Based Medicine, the consistent results from five Level III intervention studies designate that there is Level C evidence that MAX do not reduce impact loading during a single running trial.

Running shoes for preventing lower limb running injuries in adults.

Running shoes for preventing lower limb running injuries in adults.

Acute effects of minimalist shoes on biomechanical gait parameters in comparison to walking barefoot and in cushioned shoes: a randomised crossover study

Minimalist shoes are proposed to promote walking gait patterns more similar to natural barefoot gait. While there is already considerable research evaluating the effects of minimalist shoes on running biomechanics, little has been reported about the effects of minimalist shoes on kinematic and kinetic parameters during normal gait. Therefore, the purpose of this study was to compare biomechanical gait parameters between walking in non-cushioned minimalist shoes, in conventional cushioned shoes and barefoot. Kinematic (cadence, step length, foot progression angle, length of CoP) and kinetic (vGRF) parameters of 32 healthy adults were collected at preferred walking speed on an instrumented treadmill. ANOVA or Friedman- Tests were applied for between condition comparisons. In case of significant (p < 0.05) main effects, post-hoc analyses were implemented for pairwise comparisons. Significant main effects of footwear conditions were found for all parameters (p ≤ .001). Post-hoc analyses revealed that increased cushioning properties of the applied footwear are associated with increased step lengths, lengths of CoP trajectory and foot progression angle as well as a reduced cadence. Additionally, decreased cushioning resulted in increased vGRF, especially of the forefoot and rearfoot. Results indicate that footwear significantly affects biomechanical gait parameters in a group of healthy adults. The findings have implications on the use of footwear during walking gait, with special emphasis on the cushioning properties of the different conditions.

Leg stiffness during running in highly cushioned shoes with a carbon-fiber plate and traditional shoes

BackgroundNike ZoomX Vaporfly (NVF) improves running economy and performance. The biomechanical mechanisms of these shoes are not fully understood, although thicker midsoles and carbon fiber plates are considered to play an important role in the spring-like leg characteristics during running. Leg stiffness (kleg) in the spring-mass model has been commonly used to investigate spring-like running mechanics during running. Research questionDoes kleg during running differ between NVF and traditional (TRAD) shoes? MethodsEighteen male habitual forefoot and/or midfoot strike runners ran on a treadmill at 20 km/h with NVF and TRAD shoes, respectively. kleg, vertical oscillation of the center of mass (∆CoM), spatiotemporal parameters, and mechanical loading were determined. Resultskleg was 4.8% lower in the NVF shoe condition than in the TRAD condition, although no significant difference was observed. ∆CoM was not significantly different between shoe conditions. Spatiotemporal parameters and mechanical loading were also not significantly different between shoe conditions. SignificanceThe NVF shoe is well known as improving the running economy and running performance for the cause by characteristics of better spring function. Contrary to expectation, kleg and other parameters were not significantly different during running in the NVF compared to TRAD shoe at 20 km/h. These findings indicate that well-trained runners’ spring-like running mechanics would not alter even if wearing the NVF shoes.

Differences in Peak Impact Accelerations Among Foot Strike Patterns in Recreational Runners.

IntroductionRunning-related injuries (RRIs) occur from a combination of training load errors and aberrant biomechanics. Impact loading, measured by peak acceleration, is an important measure of running biomechanics that is related to RRI. Foot strike patterns may moderate the magnitude of impact load in runners. The effect of foot strike pattern on peak acceleration has been measured using tibia-mounted inertial measurement units (IMUs), but not commercially available insole-embedded IMUs. The aim of this study was to compare the peak acceleration signal associated with rearfoot (RFS), midfoot (MFS), and forefoot (FFS) strike patterns when measured with an insole-embedded IMU.Materials and MethodsHealthy runners ran on a treadmill for 1 min at three different speeds with their habitual foot strike pattern. An insole-embedded IMU was placed inside standardized neutral cushioned shoes to measure the peak resultant, vertical, and anteroposterior accelerations at impact. The Foot strike pattern was determined by two experienced observers and evaluated using high-speed video. Linear effect mixed-effect models were used to quantify the relationship between foot strike pattern and peak resultant, vertical, and anteroposterior acceleration.ResultsA total of 81% of the 187 participants exhibited an RFS pattern. An RFS pattern was associated with a higher peak resultant (0.29 SDs; p = 0.029) and vertical (1.19 SD; p < 0.001) acceleration when compared with an FFS running pattern, when controlling for speed and limb, respectively. However, an MFS was associated with the highest peak accelerations in the resultant direction (0.91 SD vs. FFS; p = 0.002 and 0.17 SD vs. RFS; p = 0.091). An FFS pattern was associated with the lowest peak accelerations in both the resultant and vertical directions. An RFS was also associated with a significantly greater peak acceleration in the anteroposterior direction (0.28 SD; p = 0.033) than an FFS pattern, while there was no difference between MFS and FFS patterns.ConclusionOur findings indicate that runners should be grouped by RFS, MFS, and FFS when comparing peak acceleration, rather than the common practice of grouping MFS and FFS together as non-RFS runners. Future studies should aim to determine the risk of RRI associated with peak accelerations from an insole-embedded IMU to understand whether the small observed differences in this study are clinically meaningful.

Highly Cushioned Shoes Improve Running Performance in Both the Absence and Presence of Muscle Damage.

ABSTRACTPurposeWe tested the hypotheses that a highly cushioned running shoe (HCS) would 1) improve incremental exercise performance and reduce the oxygen cost (Oc) of submaximal running, and 2) attenuate the deterioration in Oc elicited by muscle damage consequent to a downhill run.MethodsThirty-two recreationally active participants completed an incremental treadmill test in an HCS and a control running shoe (CON) for the determination of Oc and maximal performance. Subsequently, participants were pair matched and randomly assigned to one of the two footwear conditions to perform a moderate-intensity running bout before and 48 h after a 30-min downhill run designed to elicit muscle damage.ResultsIncremental treadmill test performance was improved (+5.7%; +1:16 min:ss; P < 0.01) in the HCS when assessed in the nondamaged state, relative to CON. This coincided with a significantly lower Oc (−3.2%; −6 mL·kg−1·km−1; P < 0.001) at a range of running speeds and an increase in the speed corresponding to 3 mM blood lactate (+3.2%; +0.4 km·h−1; P < 0.05). As anticipated, the downhill run resulted in significant changes in biochemical, histological, and perceptual markers of muscle damage, and a significant increase in Oc (+5.2%; 10.1 mL·kg−1·km−1) was observed 48 h post. In the presence of muscle damage, Oc was significantly lower in HCS (−4.6%; −10 mL·kg−1·km−1) compared with CON.ConclusionsThese results indicate that HCS improved incremental exercise performance and Oc in the absence of muscle damage and show, for the first time, that despite worsening of Oc consequent to muscle damage, improved Oc in HCS is maintained.

Metabolic cost of level, uphill, and downhill running in highly cushioned shoes with carbon-fiber plates

BackgroundCompared to conventional racing shoes, Nike Vaporfly 4% running shoes reduce the metabolic cost of level treadmill running by 4%. The reduction is attributed to their lightweight, highly compliant, and resilient midsole foam and a midsole-embedded curved carbon-fiber plate. We investigated whether these shoes also could reduce the metabolic cost of moderate uphill (+3°) and downhill (–3°) grades. We tested the null hypothesis that, compared to conventional racing shoes, highly cushioned shoes with carbon-fiber plates would impart the same ∼4% metabolic power (W/kg) savings during uphill and downhill running as they do during level running. MethodsAfter familiarization, 16 competitive male runners performed six 5-min trials (2 shoes × 3 grades) in 2 Nike marathon racing-shoe models (Streak 6 and Vaporfly 4%) on a level, uphill (+3°), and downhill (–3°) treadmill at 13 km/h (3.61 m/s). We measured submaximal oxygen uptake and carbon dioxide production during Minutes 4–5 and calculated metabolic power (W/kg) for each shoe model and grade combination. ResultsCompared to the conventional shoes (Streak 6), the metabolic power in the Vaporfly 4% shoes was 3.83% (level), 2.82% (uphill), and 2.70% (downhill) less (all p < 0.001). The percent of change in metabolic power for uphill running was less compared to level running (p = 0.04; effect size (ES) = 0.561) but was not statistically different between downhill and level running (p = 0.17; ES = 0.356). ConclusionOn a running course with uphill and downhill sections, the metabolic savings and hence performance enhancement provided by Vaporfly 4% shoes would likely be slightly less overall, compared to the savings on a perfectly level race course.

Wearing Cushioning Shoes Reduce Load Rates More Effectively in Post-Fatigue than in Pre-Fatigue during Landings.

Simple SummaryAthlete experience high impact forces during landing, which is a contributing factor to injury risk potentials. As a potential factor of affecting the impact force, previous study of the effects of footwear cushioning effect on landing biomechanics were inconsistent. Furthermore, limited efforts have been exerted on the relationship between footwear cushioning and fatigue. In this study, the footwear cushioning effects on bipedal landing biomechanics before and after acute exercise-induced fatigue protocol were explored. The results of this study suggest that footwear cushioning can reduce landing-related rearfoot impact forces regardless of fatigue conditions. In a situation where the neuromuscular activity is reduced or absent, e.g., post-fatigue, wearing better cushioning shoes show superior attenuation, as indicated by low forefoot and rearfoot impacts.Purpose: this study aimed to investigate the footwear cushioning effects on impact forces and joint kinematics of the lower extremity during bipedal drop landings before and after acute exercise-induced fatigue protocol. Methods: in this case, 15 male collegiate basketball athletes performed drop landings from a 60 cm platform wearing highly-cushioned shoes (HS) and less cushioned shoes (control shoes, CS) before and after acute fatigue-inducing exercises (i.e., shuttle run combined with multiple vertical jumps). Force plates and motion capturing systems were synchronised to measure ground reaction forces and kinematic data during drop landings. Maximum jump height was analysed with one-way ANOVA. Two-way repeated measure ANOVAs were performed on each of the tested variables to examine if there was significant main effects of shoe and fatigue as well as the interaction. The significance level was set to 0.05. Results: rearfoot peak impact forces and loading rates significantly reduced when the participants wore HS in pre- and post-fatigue conditions. The peak loading rates in forefoot significantly reduced when HS were worn in post-fatigue. Compared with pre-fatigue, wearing HS contributed to with 24% and 13% reduction in forefoot and rearfoot peak loading rates, respectively, and the occurrence times of first and second peak impact forces and loading rates were much later. In the post-fatigue, a significant increase in the initial contact and minimum angles of the ankle were observed in HS compared with CS. Conclusion: these findings suggest that footwear cushioning can reduce landing-related rearfoot impact forces regardless of fatigue conditions. In a situation where the neuromuscular activity is reduced or absent such as post-fatigue wearing better cushioning shoes show superior attenuation, as indicated by lower forefoot and rearfoot impacts.

Comparing walking biomechanics of older females in maximal, minimal, and traditional shoes

BackgroundKnee osteoarthritis (OA) is a degenerative joint disease that affects millions of individuals each year. Several biomechanical variables during walking have been identified as risk factors for developing knee OA, including the peak external knee adduction moment (KAM) and the knee flexion angle at initial contact. Many interventions have been studied to help mitigate these risk factors, including footwear. However, it is largely unknown how varying shoe cushioning may affect walking biomechanics related to knee OA risk. Research QuestionWhat is the effect of maximally and minimally cushioned shoes on walking biomechanics compared to a traditionally cushioned shoe in older females? MethodsWalking biomechanics in three shoes (maximal, traditional, minimal) were collected on 16 healthy females ages 50–70 using an 8-camera 3D motion capture system and two embedded force plates. Key biomechanical variables related to knee OA disease risk were compared between shoes using repeated measures ANOVAs. ResultsThe KAM was significantly larger in the maximal shoe (p = 0.005), while the knee flexion angle at initial contact was significantly larger in both the maximal and minimal shoe compared to the traditional shoe (p = .000). Additionally, the peak knee flexion angle (p = .000) and the loading rates of the vertical ground reaction force were (instantaneous: p = 0.001; average: p = .010) were significantly higher in the minimal shoe. SignificanceWhile these results are specific to the shoes used in this study, clinicians should exercise caution in prescribing maximal or minimal shoes to females in this age group who may be at risk of knee OA given these results. Research is needed on the effect of these shoes in patients with knee OA.

Maximalist shoes do not alter performance or joint mechanical output during the countermovement jump

ABSTRACT This study examined potential differences between maximally cushioned (MAX) shoes and standard cushioned (STND) shoes during countermovement vertical jump (CMVJ) performance. Twenty-one males (23[2] y; 86.5[15.4] kg; 179.8[6.3] cm) completed eight jumps each in MAX and STND shoes while three-dimensional kinematic and kinetic data were collected. Paired-samples t-tests (α = 0.05) and Cohen’s d effect sizes (ES) were used to compare the following variables: vertical jump displacement, jump time, hip, knee and ankle joint angles at the start of the countermovement, the end of the unloading phase, the end of the eccentric phase, and at takeoff, peak joint power, and the joint contributions to total lower extremity work during the eccentric and concentric phases. The ankle was more dorsiflexed at the end of the countermovement in the MAX shoe (p = 0.002; ES = 0.55) but greater plantarflexion occurred in the STND shoes at takeoff (p = 0.028; ES = 0.56). No other differences were observed. The result of this study suggests that unique ankle joint angular positioning may be employed when wearing MAX versus STND shoes. Since the unique ankle joint positioning did not alter jump performance, potential MAX footwear users might not need to consider the potential for altered CMVJ performance when determining whether to adopt MAX footwear.

Effects Of Minimal, Traditional, And Highly Cushioned Shoes On Injury-related Biomechanics In Rear And Non-rearfoot Strike Runners

Running barefoot, in minimal shoes, or traditional shoes alters certain injury-related biomechanical variables and these footwear effects can be influenced by foot strike pattern. It is unclear however how highly cushioned shoes might alter this interaction. PURPOSE: Given the increasing popularity in highly cushioned footwear in runners, this study assessed the interaction of footwear and foot strike pattern on injury-related biomechanical variables in experienced runners. METHODS: Six rear (RFS) and seven non-rearfoot strike (NRFS) experienced runners completed five running trials at 3.5m/s (±5%) in minimal (MSH), standard (SH) and high cushioned (HC) shoes. A mixed-design repeated measures ANOVA was used to test interaction effects for all injury-related variables. Paired t-tests were used to decipher any interaction effect and Cohen’s d effect sizes were computed to assess mean difference magnitudes. Given the preliminary nature of this work and the small sample size, alpha level was set to 0.1. RESULTS: Strike index confirmed the different strike patterns while running in SH between RFS (15.2±3.1%) and NRFS (102.8±11.8%) groups (p<0.001). Interaction effects were not observed for any of the variables except for peak eversion velocity (p=0.1) and instantaneous vertical loading rate (IVLR; p=0.1) (Figure 1). Main footwear effects were observed for IVLR (p=0.004) and peak eversion velocity (p=0.01). Main foot strike effects were observed for step length (p=0.041), strike index (p=0.00), and IVLR (p=0.00). CONCLUSION: Similar to prior research, these current preliminary findings suggest there might be an interaction between foot strike and footwear in experienced runners for peak eversion velocity and IVLR. Thus, if these biomechanical variables are of interest to scientists or clinicians, these findings suggest that footwear type and strike pattern should both be considered in research or return to running programs.Figure 1:: Instantaneous vertical loading rate (A; IVLR) and peak eversion velocity (B) in the three footwear conditions in rare (RFS; black) and non-rearfoot strike (NRFS; red) runners. *: foot strike group difference within footwear; #: footwear difference within foot strike group (p < 0.1).

Ultrasound-Based Mechanical Adaptation of Achilles Tendon After 12-Week Running with Minimalist Shoes

This study aimed to investigate the effect of a 12-week running program using minimalist shoes on ultrasoundbased mechanical adaptation of Achilles tendon (AT). Fifteen male recreational runners accustomed to run in standard cushioned shoes with rearfoot strike pattern were recruited. They were required to wear minimalist shoes without a compulsory transition in foot strike pattern, and be involved in a 12-week running program. Before and after the intervention, the cross-sectional area of AT was collected in the prone position via an ultrasound device. The ankle plantarflexion moment, recorded on an isokinetic dynamometer, was synchronized to the image changes in vivo AT length. Intraclass correlation coefficient was determined to evaluate the intraand interobserver variabilities. Paired t-test was used to quantify the effects of training program (pre- and posttraining) on each variable of the cross-sectional area, AT force, AT stress, and AT strain during an isometric contraction. Seven participants dropped out after the intervention. The results showed that the intraclass correlation coefficients for the intra- and interobserver reliabilities were good to excellent (intraclass correlation coefficients = 0.895–0.996) for the cross-sectional area and elongation. After 12-week running with minimalist shoes, plantarflexion moment, AT force, AT stress, and AT strain significantly increased during an isometric contraction (P &lt; 0.05). The mechanical adaptation of AT improved after 12-week running with minimalist shoes by more efficient energy storage and release, which could prevent or reduce the risk of injury potentially.