Effects of a minimalist shoe on running economy and 5-km running performance

Assessing the reliability of biomechanical variables during a horizontal deceleration task in healthy adults

Horizontal deceleration technique is an underpinning factor to musculoskeletal injury risk and performance in multidirectional sport. This study primarily assessed within- and between-session reliability of biomechanical and performance-based aspects of a horizontal deceleration technique and secondarily investigated the effects of limb dominance on reliability. Fifteen participants completed four horizontal decelerations on each leg during test and retest sessions. A three-dimensional motion analysis system was used to collect kinetic and kinematic data. Completion time, ground contact time, rate of horizontal deceleration, minimum centre of mass height, peak eccentric force, impulse ratio, touchdown distance, sagittal plane foot and knee angles at initial contact, maximum sagittal plane thorax angle, and maximum knee flexion moment were assessed. Coefficients of variation (COV) and intraclass correlation coefficients (ICC) were used to assess within- and between-session reliability, respectively. Seven variables showed "great" within-session reliability bilaterally (COV ≤9.13%). ICC scores were 'excellent' (≥0.91; n = 4), or 'good' (0.76-0.89; n = 7), bilaterally. Limb dominance affected five variables; three were more reliable for the dominant leg. This horizontal deceleration task was reliable for most variables, with little effect of limb dominance on reliability. This deceleration task may be reliably used to assess and track changes in deceleration technique in healthy adults.

Influence of Running Shoe Longitudinal Bending Stiffness on Running Economy and Performance in Trained and National Level Runners

INTRODUCTION/PURPOSE

Previous results about shoe longitudinal bending stiffness (LBS) and running economy (RE) show high variability. This study aimed to assess the effects of shoes with increased LBS on RE and performance in trained and national runners.

METHODS

Twenty-eight male runners were divided into two groups according to their 10-km performance times (trained, 38-45 min and national runners, <34 min). Subjects ran 2 × 3 min (at 9 and 13 km·h -1 for trained, and 13 and 17 km·h -1 for national runners) with an experimental shoe with carbon fiber plate to increase the LBS (Increased LBS) and a control shoe (without carbon fiber plate). We measured energy cost of running (W·kg -1 ) and spatiotemporal parameters in visit one and participants performed a 3000 m time trial (TT) in two successive visits.

RESULTS

Increased LBS improved RE in the trained group at slow (11.41 ± 0.93 W·kg -1 vs 11.86 ± 0.93 W·kg -1 ) and fast velocity (15.89 ± 1.24 W·kg -1 vs 16.39 ± 1.24 W·kg -1 ) and only at the fast velocity in the national group (20.35 ± 1.45 W·kg -1 vs 20.78 ± 1.18 W·kg -1 ). The improvements in RE were accompanied by different changes in biomechanical variables between groups. There were a similar improvement in the 3000 m TT test in Increased LBS for trained (639 ± 59 vs 644 ± 61 s in control shoes) and national runners (569 ± 21 vs 574 ± 21 s in control shoes) with more constant pace in increased LBS compared with control shoes in both groups.

CONCLUSIONS

Increasing shoe LBS improved RE at slow and fast velocities in trained runners and only at fast velocity in national runners. However, the 3000 m TT test improved similarly in both levels of runners with increased LBS. The improvements in RE are accompanied by small modifications in running kinematics that could explain the difference between the different levels of runners.

Influence of the World Athletics Stack Height Regulation on Track Running Performance

ABSTRACT

Ruiz-Alias, SA, Pérez-Castilla, A, Soto-Hermoso, VM, and García-Pinillos, F. Influence of the world athletics stack height regulation on track running performance. J Strength Cond Res 37(11): 2260-2266, 2023-A new footwear regulation based on limiting the stack height (i.e., amount of material between the feet and the ground) has been established by World Athletics to ensure that performance is achieved through the primacy of human effort over technology in running shoes. Analyzing the effect of legal and illegal shoes on running performance is therefore needed to determine its effectiveness. Thus, this study aimed (a) to compare the effect of 2 footwear models categorized as legal and illegal by the World Athletics regulation on track running performance and (b) to analyze the derived metrics of the athletes' biomechanics when using each footwear model at racing paces. Within 1 week, 14 highly trained athletes performed 2 testing sessions composed of 2 time trials of 9- and 3-minute duration with 30 minutes of recovery between them. The athletes wore the "Nike ZoomX Dragonfly" track spikes model and the "Nike ZoomX Vaporfly Next % 2" marathon shoe model in a counterbalanced randomized order. The results revealed that (a) there was only a small worthwhile improvement in the 3-minute time trial when using the marathon shoes of 0.97% (-0.04 to 1.98%) and (b) there was a main effect of footwear in 7 of the 9 biomechanical variables analyzed (p ≤ 0.050). The ground contact time was the unique performance predictor (p = 0.005, adjusted R2 = 0.476). Altogether, the use of legal and illegal running shoes altered the runners form, which only influenced the mid-distance performance.

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.

The effect of footwear on mechanical behaviour of the human ankle plantar-flexors in forefoot runners

Purpose

To compare the ankle plantar-flexor muscle-tendon mechanical behaviour during barefoot and shod forefoot running.

Methods

Thirteen highly trained forefoot runners performed five overground steady-state running trials (4.5 ± 0.5 m^.s^-1) while barefoot and shod. Three-dimensional kinematic and ground reaction force data were collected and used as inputs for musculoskeletal modelling. Muscle-tendon behaviour of the ankle plantar-flexors (soleus; medial gastrocnemius; and lateral gastrocnemius) were estimated across the stance phase and compared between barefoot and shod running using a two-way multivariate analysis of variance.

Results

During barefoot running peak muscle-tendon unit (MTU) power generation was 16.5% (p = 0.01) higher compared to shod running. Total positive MTU work was 18.5% (p = 0.002) higher during barefoot running compared to shod running. The total sum of tendon elastic strain energy was 8% (p = 0.036) greater during barefoot compared to shod running, however the relative contribution of tendon and muscle fibres to muscle-tendon unit positive work was not different between conditions.

Conclusion

Barefoot forefoot running demands greater muscle and tendon work than shod forefoot running, but the relative contribution of tendon strain energy to overall muscle-tendon unit work was not greater.

Seven-Weeks Gait-Retraining in Minimalist Footwear Has No Effect on Dynamic Stability Compared With Conventional Footwear

Purpose: To investigate the effects of two different running footwear conditions (transition to minimalist footwear and conventional running footwear) on dynamic postural stability before and after 7 weeks of gait retraining program, and to evaluate the effect of fatigue on dynamic stability. Method: This randomized controlled clinical trial was carried out by 42 recreational male runners, who were randomly divided into two groups; Conventional Footwear Group (CFG) (n = 22) and Minimalist Footwear Group (MFG) (n = 20). Dynamic Postural Stability Index (DPSI), in a fatigued and non-fatigued state, were assessed before and after a gait retraining program. The gait retraining program consisted of three guided training sessions per week for 7 weeks. Training program was mainly focused on running technique and submaximal aerobic training with step-frequency exercises. Minimalist footwear was progressively introduced in the MFG. The CFG and MFG performed the same training exercises and a full body conditioning program. Fatigue was induced using a 30-minute running test at individual 85% of the maximal aerobic speed. Results: No differences in dynamic stability variables were found between MFG and CFG in any of the study condition. MFG and CFG showed better dynamic stability after the intervention program (CFG: 13.1% of change, DPSIpre = 0.3221 ± 0.04, DPSIpost = 0.2799 ± 0.04; p < .05; MFG: 6.7% of change, DPSIpre = 0.3117 ± 0.04, DPSIpost = 0.2907 ± 0.05). Finally, dynamic stability was significatively lower in both groups after fatigue protocol (p < .05). Conclusions: Following a 7-week gait retraining program, footwear did not affect the results, being the gait retraining program more relevant on improving dynamic stability.

Carbon Plate Shoes Improve Metabolic Power and Performance in Recreational Runners

This study compared metabolic power (MP) and time trial (TT) running performance between Adidas Adizero Adios (AAA) and Nike VaporFly 4% (NVP). Thirty-seven runners completed three laboratory sessions and two field sessions (n=30). After familiarization (visit 1), participants completed eight 6-min treadmill running bouts (four with each shoe, counterbalanced) at their preferred pace, and MP was assessed using indirect calorimetry (visits 2 and 3). During visits 4 and 5, participants completed two outdoor TTs (~3.5 km) in NVP and AAA (counterbalanced). Compared with AAA, NVP exhibited superior MP (NVP: median=13.88 (Q1-Q3=12.90-15.08 W/kg; AAA: median=14.08 (Q1-Q3=13.12-15.44 W/kg; z=-4.81, p<.001, effect size=.56) and TT (NVP=793±98 s; AAA=802±100 s, p=.001; effect size=.09). However, there was no relationship between changes in MP and changes in TT between shoes (r=.151 p=.425, 95% confidence interval=[-.22; .48]). Our results demonstrate that NVP, compared with AAA, improves MP and TT in recreational runners. The lack of correlation between changes in MP and TT indicates that factors other than improved MP contribute to faster short-distance TT with NVP.

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.

Adding carbon fiber to shoe soles may not improve running economy: a muscle-level explanation

In an attempt to improve their distance-running performance, many athletes race with carbon fiber plates embedded in their shoe soles. Accordingly, we sought to establish whether, and if so how, adding carbon fiber plates to shoes soles reduces athlete aerobic energy expenditure during running (improves running economy). We tested 15 athletes as they ran at 3.5 m/s in four footwear conditions that varied in shoe sole bending stiffness, modified by carbon fiber plates. For each condition, we quantified athlete aerobic energy expenditure and performed biomechanical analyses, which included the use of ultrasonography to examine soleus muscle dynamics in vivo. Overall, increased footwear bending stiffness lengthened ground contact time (p = 0.048), but did not affect ankle (p ≥ 0.060), knee (p ≥ 0.128), or hip (p ≥ 0.076) joint angles or moments. Additionally, increased footwear bending stiffness did not affect muscle activity (all seven measured leg muscles (p ≥ 0.146)), soleus active muscle volume (p = 0.538; d = 0.241), or aerobic power (p = 0.458; d = 0.04) during running. Hence, footwear bending stiffness does not appear to alter the volume of aerobic energy consuming muscle in the soleus, or any other leg muscle, during running. Therefore, adding carbon fiber plates to shoe soles slightly alters whole-body and calf muscle biomechanics but may not improve running economy.

Influence of Shoe Mass on Performance and Running Economy in Trained Runners

Purpose

The aim of this study was to assess the effects of adding shoe mass on running economy (RE), gait characteristics, neuromuscular variables and performance in a group of trained runners.

Methods

Eleven trained runners (6 men and 5 women) completed four evaluation sessions separated by at least 7 days. The first session consisted of a maximal incremental test where the second ventilatory threshold (VT₂) and the speed associated to the VO_2max (vVO_2max) were calculated. In the next sessions, RE at 75, 85, and 95% of the VT₂ and the time to exhaustion (TTE) at vVO_2max were assessed in three different shoe mass conditions (control, +50 g and +100 g) in a randomized, counterbalanced crossover design. Biomechanical and neuromuscular variables, blood lactate and energy expenditure were measured during the TTE test.

Results

RE worsened with the increment of shoe mass (Control vs. 100 g) at 85% (7.40%, 4.409 ± 0.29 and 4.735 ± 0.27 kJ⋅kg⁻¹⋅km⁻¹, p = 0.021) and 95% (10.21%, 4.298 ± 0.24 and 4.737 ± 0.45 kJ⋅kg⁻¹⋅km⁻¹, p = 0.005) of VT₂. HR significantly increased with the addition of mass (50 g) at 75% of VT₂ (p = 0.01) and at 75, 85, and 95% of VT₂ (p = 0.035, 0.03, and 0.03, respectively) with the addition of 100 g. TTE was significantly longer (∼22%, ∼42 s, p = 0.002, ES = 0.149) in the Control condition vs. 100 g condition, but not between Control vs. 50 g (∼24 s, p = 0.094, ES = 0.068).

Conclusion

Overall, our findings suggest that adding 100 g per shoe impairs running economy and performance in trained runners without changes in gait characteristics or neuromuscular variables. These findings further support the use of light footwear to optimize running performance.

Shoe feature recommendations for different running levels: A Delphi study

Providing runners with footwear that match their functional needs has the potential to improve footwear comfort, enhance running performance and reduce the risk of overuse injuries. It is currently not known how footwear experts make decisions about different shoe features and their properties for runners of different levels. We performed a Delphi study in order to understand: 1) definitions of different runner levels, 2) which footwear features are considered important and 3) how these features should be prescribed for runners of different levels. Experienced academics, journalists, coaches, bloggers and physicians that examine the effects of footwear on running were recruited to participate in three rounds of a Delphi study. Three runner level definitions were refined throughout this study based on expert feedback. Experts were also provided a list of 20 different footwear features. They were asked which features were important and what the properties of those features should be. Twenty-four experts, most with 10+ years of experience, completed all three rounds of this study. These experts came to a consensus for the characteristics of three different running levels. They indicated that 12 of the 20 footwear features initially proposed were important for footwear design. Of these 12 features, experts came to a consensus on how to apply five footwear feature properties for all three different running levels. These features were: upper breathability, forefoot bending stiffness, heel-to-toe drop, torsional bending stiffness and crash pad. Interestingly, the experts were not able to come to a consensus on one of the most researched footwear features, rearfoot midsole hardness. These recommendations can provide a starting point for further biomechanical studies, especially for features that are considered as important, but have not yet been examined experimentally.

Optimisation of assessment of maximal rate of heart rate increase for tracking training-induced changes in endurance exercise performance

The maximal rate of heart rate (HR) increase (rHRI), a marker of HR acceleration during transition from rest to submaximal exercise, correlates with exercise performance. In this cohort study, whether rHRI tracked performance better when evaluated over shorter time-periods which include a greater proportion of HR acceleration and less steady-state HR was evaluated. rHRI and five-km treadmill running time-trial performance (5TTT) were assessed in 15 runners following one week of light training (LT), two weeks of heavy training (HT) and 10-day taper (T). rHRI was the first derivative maximum of a sigmoidal curve fit to one, two, three and four minutes of R-R data during transition from rest to running at 8 km/h (rHRI_8 km/h), 10.5 km/h_, 13 km/h and transition from 8 to 13 km/h (rHRI_8–13km/h). 5TTT time increased from LT to HT (effect size [ES] 1.0, p < 0.001) then decreased from HT to T (ES −1.7, p < 0.001). 5TTT time was inversely related to rHRI_8 km/h assessed over two (B = −5.54, p = 0.04) three (B = −5.34, p = 0.04) and four (B = −5.37, p = 0.04) minutes, and rHRI_8–13km/h over one (B = −11.62, p = 0.006) and three (B = −11.44, p = 0.03) minutes. 5TTT correlated most consistently with rHRI_8 km/h. rHRI_8 km/h assessed over two to four minutes may be suitable for evaluating athlete responses to training.

Are changes in running economy associated with changes in performance in runners? A systematic review and meta-analysis

Improvements in running economy (RE) are thought to lead to improvements in running performance (P). Multiple interventions have been designed with the aim of improving RE in middle and long-distance runners. The aim of this study was to assess the effect of interventions of at least 2-weeks' duration on RE and P and to determine whether there is a relationship between changes in RE (ΔRE) and changes in running performance (ΔP). A database search was carried out in Web of Science, Scopus and SPORTDiscus. In accordance with a PRISMA checklist 10 studies reporting 12 comparisons between interventions and controls were included in the review. There was no correlation between percentage ΔRE and percentage ΔP (r = 0.46, P = 0.936, 12 comparisons). There was a low risk of reporting bias but an unclear risk of bias for other items. Meta-analyses found no statistically significant differences between interventions and controls for RE (SMD (95% CI) = -0.37 (-1.43, 0.69), 204 participants, p = 0.49) or for P (SMD (95% CI) = -0.65 (-26.02, 24.72, 204 participants, p = 0.99). There is a need for studies of greater statistical power, methodological quality, duration and homogeneity of intervention and population. Standardised measures of performance and greater control over non-intervention training are also required.

Detrended fluctuation analysis detects altered coordination of running gait in athletes following a heavy period of training

OBJECTIVES

To investigate whether functional overreaching affects locomotor system behaviour when running at fixed relative intensities and if any effects were associated with changes in running performance.

DESIGN

Prospective intervention study.

METHODS

Ten trained male runners completed three training blocks in a fixed order. Training consisted of one week of light training (baseline), two weeks of heavy training designed to induce functional overreaching, and ten days of light taper training designed to allow athletes to recover from, and adapt to, the heavy training. Locomotor behaviour, 5-km time trial performance, and subjective reports of training status (Daily Analysis of Life Demands for Athletes (DALDA) questionnaire) were assessed at the completion of each training block. Locomotor behaviour was assessed using detrended fluctuation analysis of stride intervals during running at speeds corresponding to 65% and 85% of maximum heart rate (HR_max) at baseline.

RESULTS

Time trial performance (effect size ±95% confidence interval (ES): 0.16±0.06; p<0.001), locomotor behaviour at 65% HR_max (ES: -1.12±0.95; p=0.026), and DALDA (ES: 2.55±0.80; p<0.001) were all detrimentally affected by the heavy training. Time trial performance improved relative to baseline after the taper (ES: -0.16±0.10; p=0.003) but locomotor behaviour at 65% HR_max (ES: -1.18±1.17; p=0.048) and DALDA (ES: 0.92±0.90; p=0.045) remained impaired.

CONCLUSIONS

Locomotor behaviour during running at 65% HR_max was impaired by functional overreaching and remained impaired after a 10-day taper, despite improved running performance. Locomotor changes may increase injury risk and should be considered within athlete monitoring programs independently of performance changes.

Improving Running Economy by Transitioning to Minimalist Footwear: A Randomised Controlled Trial

OBJECTIVES

Ongoing debates about benefits and risks of barefoot- and minimally-shod running have, to date, revealed no conclusive findings for long-term effects on physical performance. The purpose of this study was to examine the effects of an 8-week transition to minimalist footwear (MFW) on running economy (RE).

DESIGN

Randomised controlled trial.

METHODS

Thirty-two male, habitually-shod runners were assigned randomly to an 8-week training intervention either in minimalist (=intervention group) or conventional running shoes (=control group). The intervention consisted of a gradual increase in use of the new footwear by 5% of the individual weekly distance. Before and after the intervention, a VO₂max test was followed by a submaximal RE test at 70% and 80% of vVO₂max in both shoe conditions 7days later. RE was measured at the submaximal tests and expressed as caloric unit cost (kcalkg^-1km^-1) and oxygen consumption (mlkg^-1km^-1).

RESULTS

RE improved in the intervention group over time compared to the control group with small to moderate effect sizes (ES) in both shoe conditions: Effects on RE (kcalkg^-1km^-1) in conventional running shoes: ES vVO₂70%: 0.68 (95% CI: -0.14 to 1.51), ES vVO₂80%: 0.78 (95% CI: 0-1.56). In minimalist footwear: ES vVO₂70%: 0.3 (95% CI: -0.54 to 1.14), ES vVO₂80%: 0.42 (95% CI: -0.41 to 1.25). These effects were not statistically significant (p>0.05). The repeated-measures ANOVA also showed no group by time interactions for all submaximal RE testing conditions (p>0.05).

CONCLUSIONS

Although not reaching statistical significance, training in MFW compared to CRS resulted in small to moderate improvements in RE.

Six-week transition to minimalist shoes improves running economy and time-trial performance

OBJECTIVES

This study investigated if gradually introducing runners to minimalist shoes during training improved running economy and time-trial performance compared to training in conventional shoes. Changes in stride rate, stride length, footfall pattern and ankle plantar-flexor strength were also investigated.

DESIGN

Randomised parallel intervention trial.

METHODS

61 trained runners gradually increased the amount of running performed in either minimalist (n=31) or conventional (n=30) shoes during a six-week standardised training program. 5-km time-trial performance, running economy, ankle plantar-flexor strength, footfall pattern, stride rate and length were assessed in the allocated shoes at baseline and after training. Footfall pattern was determined from the time differential between rearfoot and forefoot (TD_R-F) pressure sensors.

RESULTS

The minimalist shoe group improved time-trial performance (effect size (ES): 0.24; 95% confidence interval (CI): 0.01, 0.48; p=0.046) and running economy (ES 0.48; 95%CI: 0.22, 0.74; p<0.001) more than the conventional shoe group. There were no minimalist shoe training effects on ankle plantar-flexor concentric (ES: 0.11; 95%CI: -0.18, 0.41; p=0.45), isometric (ES: 0.23; 95%CI: -0.17, 0.64; p=0.25), or eccentric strength (ES: 0.24; 95%CI: -0.17, 0.65; p=0.24). Minimalist shoes caused large reductions in TD_R-F (ES: 1.03; 95%CI: 0.65, 1.40; p<0.001) but only two runners changed to a forefoot footfall. Minimalist shoes had no effect on stride rate (ES: 0.04; 95%CI: -0.08, 0.16; p=0.53) or length (ES: 0.06; 95%CI: -0.06, 0.18; p=0.35).

CONCLUSIONS

Gradually introducing minimalist shoes over a six-week training block is an effective method for improving running economy and performance in trained runners.