Dissociation between running economy and running performance in elite Kenyan distance runners

Influence of energy availability on metabolic hormonal profiles in east African female and male distance runners

BACKGROUND

Energy availability (EA) and relative energy deficiency in sport (RED-S) are understudied in East African endurance athletes, both females (F) and males (M). This study assessed the metabolic hormonal profiles of such athletes relative to their EA status.

METHODS

Forty athletes (F=16, M=24) had their EA status, training, maximal oxygen uptake, and resting blood samples assessed using standard research practices. Subjects were stratified into two groups, high EA (HiEA) and low EA (LoEA) based on combined median value.

RESULTS

Cortisol (P=0.034) and insulin (P=0.044) were significantly elevated in the LoEA group, while growth hormone (P=0.045) was significantly suppressed; and, prolactin (P=0.078) trended towards suppression, respectively compared to the HiEA group. All other hormonal comparison were non-significant.

CONCLUSIONS

Metabolic hormonal profiles of female and male African distance runners are affected by their EA status. Aspects of these alterations agree in part with published findings based upon White populations, although some differences exist and need further investigation.

The Relationship Between Running Biomechanics and Running Economy: A Systematic Review and Meta-Analysis of Observational Studies

BACKGROUND

Running biomechanics is considered an important determinant of running economy (RE). However, studies examining associations between running biomechanics and RE report inconsistent findings.

OBJECTIVE

The aim of this systematic review was to determine associations between running biomechanics and RE and explore potential causes of inconsistency.

METHODS

Three databases were searched and monitored up to April 2023. Observational studies were included if they (i) examined associations between running biomechanics and RE, or (ii) compared running biomechanics between groups differing in RE, or (iii) compared RE between groups differing in running biomechanics during level, constant-speed, and submaximal running in healthy humans (18-65 years). Risk of bias was assessed using a modified tool for observational studies and considered in the results interpretation using GRADE. Meta-analyses were performed when two or more studies reported on the same outcome. Meta-regressions were used to explore heterogeneity with speed, coefficient of variation of height, mass, and age as continuous outcomes, and standardization of running shoes, oxygen versus energetic cost, and correction for resting oxygen or energy cost as categorical outcomes.

RESULTS

Fifty-one studies (n = 1115 participants) were included. Most spatiotemporal outcomes showed trivial and non-significant associations with RE: contact time r = - 0.02 (95% confidence interval [CI] - 0.15 to 0.12); flight time r = 0.11 (- 0.09 to 0.32); stride time r = 0.01 (- 0.8 to 0.50); duty factor r = - 0.06 (- 0.18 to 0.06); stride length r = 0.12 (- 0.15 to 0.38), and swing time r = 0.12 (- 0.13 to 0.36). A higher cadence showed a small significant association with a lower oxygen/energy cost (r = - 0.20 [- 0.35 to - 0.05]). A smaller vertical displacement and higher vertical and leg stiffness showed significant moderate associations with lower oxygen/energy cost (r = 0.35, - 0.31, - 0.28, respectively). Ankle, knee, and hip angles at initial contact, midstance or toe-off as well as their range of motion, peak vertical ground reaction force, mechanical work variables, and electromyographic activation were not significantly associated with RE, although potentially relevant trends were observed for some outcomes.

CONCLUSIONS

Running biomechanics can explain 4-12% of the between-individual variation in RE when considered in isolation, with this magnitude potentially increasing when combining different variables. Implications for athletes, coaches, wearable technology, and researchers are discussed in the review.

PROTOCOL REGISTRATION

https://doi.org/10.17605/OSF.IO/293 ND (OpenScience Framework).

A simulation framework to determine optimal strength training and musculoskeletal geometry for sprinting and distance running

Musculoskeletal geometry and muscle volumes vary widely in the population and are intricately linked to the performance of tasks ranging from walking and running to jumping and sprinting. As an alternative to experimental approaches, where it is difficult to isolate factors and establish causal relationships, simulations can be used to independently vary musculoskeletal geometry and muscle volumes, and develop a fundamental understanding. However, our ability to understand how these parameters affect task performance has been limited due to the high computational cost of modelling the necessary complexity of the musculoskeletal system and solving the requisite multi-dimensional optimization problem. For example, sprinting and running are fundamental to many forms of sport, but past research on the relationships between musculoskeletal geometry, muscle volumes, and running performance has been limited to observational studies, which have not established cause-effect relationships, and simulation studies with simplified representations of musculoskeletal geometry. In this study, we developed a novel musculoskeletal simulator that is differentiable with respect to musculoskeletal geometry and muscle volumes. This simulator enabled us to find the optimal body segment dimensions and optimal distribution of added muscle volume for sprinting and marathon running. Our simulation results replicate experimental observations, such as increased muscle mass in sprinters, as well as a mass in the lower end of the healthy BMI range and a higher leg-length-to-height ratio in marathon runners. The simulations also reveal new relationships, for example showing that hip musculature is vital to both sprinting and marathon running. We found hip flexor and extensor moment arms were maximized to optimize sprint and marathon running performance, and hip muscles the main target when we simulated strength training for sprinters. Our simulation results provide insight to inspire future studies to examine optimal strength training. Our simulator can be extended to other athletic tasks, such as jumping, or to non-athletic applications, such as designing interventions to improve mobility in older adults or individuals with movement disorders.

More than energy cost: multiple benefits of the long Achilles tendon in human walking and running

Elastic strain energy that is stored and released from long, distal tendons such as the Achilles during locomotion allows for muscle power amplification as well as for reduction of the locomotor energy cost: as distal tendons perform mechanical work during recoil, plantar flexor muscle fibres can work over smaller length ranges, at slower shortening speeds, and at lower activation levels. Scant evidence exists that long distal tendons evolved in humans (or were retained from our more distant Hominoidea ancestors) primarily to allow high muscle-tendon power outputs, and indeed we remain relatively powerless compared to many other species. Instead, the majority of evidence suggests that such tendons evolved to reduce total locomotor energy cost. However, numerous additional, often unrecognised, advantages of long tendons may speculatively be of greater evolutionary advantage, including the reduced limb inertia afforded by shorter and lighter muscles (reducing proximal muscle force requirement), reduced energy dissipation during the foot-ground collisions, capacity to store and reuse the muscle work done to dampen the vibrations triggered by foot-ground collisions, reduced muscle heat production (and thus core temperature), and attenuation of work-induced muscle damage. Cumulatively, these effects should reduce both neuromotor fatigue and sense of locomotor effort, allowing humans to choose to move at faster speeds for longer. As these benefits are greater at faster locomotor speeds, they are consistent with the hypothesis that running gaits used by our ancestors may have exerted substantial evolutionary pressure on Achilles tendon length. The long Achilles tendon may therefore be a singular adaptation that provided numerous physiological, biomechanical, and psychological benefits and thus influenced behaviour across multiple tasks, both including and additional to locomotion. While energy cost may be a variable of interest in locomotor studies, future research should consider the broader range of factors influencing our movement capacity, including our decision to move over given distances at specific speeds, in order to understand more fully the effects of Achilles tendon function as well as changes in this function in response to physical activity, inactivity, disuse and disease, on movement performance.

Variability in Running Economy of Kenyan World-Class and European Amateur Male Runners with Advanced Footwear Running Technology: Experimental and Meta-analysis Results

BACKGROUND

Advanced footwear technology improves average running economy compared with racing flats in sub-elite athletes. However, not all athletes benefit as performance changes vary from a 10% drawback to a 14% improvement. The main beneficiaries from such technologies, world-class athletes, have only been analyzed using race times.

OBJECTIVE

The aim of this study was to measure running economy on a laboratory treadmill in advanced footwear technology compared to a traditional racing flat in world-class Kenyan (mean half-marathon time: 59:30 min:s) versus European amateur runners.

METHODS

Seven world-class Kenyan and seven amateur European male runners completed a maximal oxygen uptake assessment and submaximal steady-state running economy trials in three different models of advanced footwear technology and a racing flat. To confirm our results and better understand the overall effect of new technology in running shoes, we conducted a systematic search and meta-analysis.

RESULTS

Laboratory results revealed large variability in both world-class Kenyan road runners, which ranged from a 11.3% drawback to a 11.4% benefit, and amateur Europeans, which ranged from a 9.7% benefit to a 1.1% drawback in running economy of advanced footwear technology compared to a flat. The post-hoc meta-analysis revealed an overall significant medium benefit of advanced footwear technology on running economy compared with traditional flats.

CONCLUSIONS

Variability of advanced footwear technology performance appears in both world-class and amateur runners, suggesting further testing should examine such variability to ensure validity of results and explain the cause as a more personalized approach to shoe selection might be necessary for optimal benefit.

How do differences in Achilles' tendon moment arm lengths affect muscle-tendon dynamics and energy cost during running?

Introduction

The relationship between the Achilles tendon moment arm length (AT_MA) and the energy cost of running (E_run) has been disputed. Some studies suggest a short AT_MA reduces E_run while others claim a long AT_MA reduces E_run. For a given ankle joint moment, a short AT_MA permits a higher tendon strain energy storage, whereas a long AT_MA reduces muscle fascicle force and muscle energy cost but shortening velocity is increased, elevating the metabolic cost. These are all conflicting mechanisms to reduce E_run, since AT energy storage comes at a metabolic cost. Neither of these proposed mechanisms have been examined together.

Methods

We measured AT_MA using the tendon travel method in 17 males and 3 females (24 ± 3 years, 75 ± 11 kg, 177 ± 7 cm). They ran on a motorized treadmill for 10 min at 2.5 m · s^-1 while E_run was measured. AT strain energy storage, muscle lengths, velocities and muscle energy cost were calculated during time-normalized stance from force and ultrasound data. A short (SHORT n = 11, AT_MA = 29.5 ± 2.0 mm) and long (LONG, n = 9, AT_MA = 36.6 ± 2.5 mm) AT_MA group was considered based on a bimodal distribution of measured AT_MA.

Results

Mean E_run was 4.9 ± 0.4 J · kg^-1 · m^-1. The relationship between AT_MA and E_run was not significant (r ² = 0.13, p = 0.12). Maximum AT force during stance was significantly lower in LONG (5,819 ± 1,202 N) compared to SHORT (6,990 ± 920 N, p = 0.028). Neither AT stretch nor AT strain energy storage was different between groups (mean difference: 0.3 ± 1 J · step^-1, p = 0.84). Fascicle force was significantly higher in SHORT (508 ± 93 N) compared to LONG (468 ± 84 N. p = 0.02). Fascicle lengths and velocities were similar between groups (p > 0.72). Muscle energy cost was significantly lower in LONG (0.028 ± 0.08 J · kg · step^-1) compared to SHORT (0.045 ± 0.14 J · kg · step^-1 p = 0.004). There was a significant negative relationship between AT_MA and total muscle energy cost relative to body mass across the stance phase (r = -0.699, p < 0.001).

Discussion

Together these results suggest that a LONG AT_MA serves to potentially reduce E_run by reducing the muscle energy cost of the plantarflexors during stance. The relative importance of AT energy storage and return in reducing E_run should be re-considered.

The Energetic Costs of Uphill Locomotion in Trail Running: Physiological Consequences Due to Uphill Locomotion Pattern-A Feasibility Study

The primary aim of our feasibility reporting was to define physiological differences in trail running (TR) athletes due to different uphill locomotion patterns, uphill running versus uphill walking. In this context, a feasibility analysis of TR athletes' cardiopulmonary exercise testing (CPET) data, which were obtained in summer 2020 at the accompanying sports medicine performance center, was performed. Fourteen TR athletes (n = 14, male = 10, female = 4, age: 36.8 ± 8.0 years) were evaluated for specific physiological demands by outdoor CPET during a short uphill TR performance. The obtained data of the participating TR athletes were compared for anthropometric data, CPET parameters, such as V˙Emaximum, V˙O2maximum, maximal breath frequency (BF_max) and peak oxygen pulse as well as energetic demands, i.e., the energy cost of running (C_r). All participating TR athletes showed excellent performance data, whereby across both different uphill locomotion strategies, significant differences were solely revealed for V˙Emaximum (p = 0.033) and time to reach mountain peak (p = 0.008). These results provide new insights and might contribute to a comprehensive understanding of cardiorespiratory consequences to short uphill locomotion strategy in TR athletes and might strengthen further scientific research in this field.

Sources of information used by elite distance running coaches for selection decisions

Talent identification and selection are critical components of competitive sport success. Despite the time, effort, and resources invested, the accuracy of selection decisions remains generally poor. While much of the scholarship in this area has focused on the factors discriminating skilled and less-skilled individuals, limited research exists on what information is used in the decision-making process for athlete selection. The current study seeks to gain a better understanding of the information used by elite distance running coaches when forming judgements for athlete selection. Ten semi-structured interviews with elite distance running coaches from across Canada were transcribed and analyzed using inductive thematic analysis. It was interpreted that coaches mainly gather information using their coach’s eye to determine an athlete’s ‘fit’ to the team. Coaches also use more objective information such as race times and movement analyses to assess performance and judge future ‘potential’. As well, the decisions were believed to be influenced by situational considerations at the time of the selection procedure. Specifically, these considerations affecting a coach’s selection included length of time to make a decision, personal limitations in decision-making abilities, and team circumstances. Interestingly, coaches recognized limitations in their selection practices and procedures and discussed some of their personal and system-level biases, highlighting their awareness of potential selection inefficiencies/inaccuracies. Overall, distance running coaches used a variety of techniques to gather information before a selection was made, relying on both subjective and objective information for crafting judgments. Findings are discussed in relation to implications for coaches, sport organizations, and talent identification and selection programs.

Does the Achilles Tendon Influence Foot Strike Patterns During an Exhaustive Run?

The study purpose was to investigate whether there is a relationship between the Achilles tendon (AT) length, moment arm length, and the foot strike pattern (FP) change during an exhaustive run (EXR) in nonrearfoot FP runners. Twenty-eight runners were recruited and divided into 2 groups (highly trained/moderately trained) according to their weekly training volume. Participants underwent the graded exercise test, the EXR with biomechanical analysis at the beginning, and at the end, and the magnetic resonance imaging scan of the AT. Correlations were used to assess associations between FP change (value of the difference between end and beginning) and the selected performance and AT variables. AT length significantly correlated with the FP change according to foot strike angle (r = -.265, P = .049). The AT moment arm length significantly correlated with the FP change according to strike index during EXR (r = -.536, P = .003). Multiple regression showed that AT length was a significant predictor for the FP change according to foot strike angle if the second predictor was the graded exercise test duration and the third predictor was training group association. These results suggest that a runner's training volume, along with a longer AT and AT moment arm appear to be associated with the ability to maintain a consistent FP during EXR by nonrearfoot FP runners.

Non-South East Asians have a better running economy and different anthropometrics and biomechanics than South East Asians

Running biomechanics and ethnicity can influence running economy (RE), which is a critical factor of running performance. Our aim was to compare RE of South East Asian (SEA) and non-South East Asian (non-SEA) runners at several endurance running speeds (10-14 km/h) matched for on-road racing performance and sex. Secondly, we explored anthropometric characteristics and relationships between RE and anthropometric and biomechanical variables. SEA were 6% less economical (p = 0.04) than non-SEA. SEA were lighter and shorter than non-SEA, and had lower body mass indexes and leg lengths (p ≤ 0.01). In terms of biomechanics, a higher prevalence of forefoot strikers in SEA than non-SEA was seen at each speed tested (p ≤ 0.04). Furthermore, SEA had a significantly higher step frequency (p = 0.02), shorter contact time (p = 0.04), smaller footstrike angle (p < 0.001), and less knee extension at toe-off (p = 0.03) than non-SEA. Amongst these variables, only mass was positively correlated to RE for both SEA (12 km/h) and non-SEA (all speeds); step frequency, negatively correlated to RE for both SEA (10 km/h) and non-SEA (12 km/h); and contact time, positively correlated to RE for SEA (12 km/h). Despite the observed anthropometric and biomechanical differences between cohorts, these data were limited in underpinning the observed RE differences at a group level. This exploratory study provides preliminary indications of potential differences between SEA and non-SEA runners warranting further consideration. Altogether, these findings suggest caution when generalizing from non-SEA running studies to SEA runners.

Relationship Between Body Segment Mass and Running Performance in Well-Trained Endurance Runners

This study examined the relationship between body segment mass and running performance in endurance runners. The total (muscle, fat, and bone masses), lean (muscle mass), and fat masses of the leg, arm, and trunk segments in 37 well-trained endurance runners were measured using dual-energy X-ray absorptiometer. The relative segment mass was calculated by normalizing the absolute mass to body mass. There were no significant correlations between absolute total, lean, and fat masses of all 3 segments and personal best 5000-m race time. No significant correlations were also observed between all 3 relative masses of the arm segment and personal best 5000-m race time. In contrast, medium positive correlations were observed between the relative total and lean masses of the leg segment and personal best 5000-m race time (r = .387 and .335, respectively, both P ≤ .031). Furthermore, large negative correlations were observed between the relative total and lean masses of the trunk segment and personal best 5000-m race time (r = -.500 and -.548, respectively, both P ≤ .002). These findings suggest that a mass distribution with smaller leg mass and greater trunk mass may be advantageous for achieving better running performance in endurance runners.

Prevalence of Triad-RED-S symptoms in high-level Kenyan male and female distance runners and corresponding control groups

PURPOSE

This study examined and compared select Triad-RED-S components/risk factors in high-level Kenyan male and female distance runners to corresponding control groups; focusing on examining energy intake (EI), bone indices, and hormonal markers.

METHODS

A cross-sectional, observational design was used in which Kenyan male and female (n = 30 and n = 26, respectively) middle- and long-distance runners and corresponding male and female control groups (n = 29 and n = 29, respectively) were examined. The participant's bone mineral density (BMD) at the lumbar spine, right femur, and total body were measured using a dual-energy X-ray absorptiometry analysis. Complete blood counts (CBC) were done on the whole blood specimens and hormonal measurements were performed on plasma specimens. In addition, athletes completed metabolic testing to determine maximal oxygen uptakes and 7-day dietary diaries.

RESULTS

Overall daily EI across runners and controls within each sex were low, but not significantly different (p > 0.05). Prevalence of low BMD values (Z score < - 2.0) was comparable across groups in each sex (p > 0.05). CBC measures suggested that both runners and controls were healthy. Finally, slight hormonal differences between runners and their respective controls existed (p < 0.05), but were not clinically meaningful or observed in typical Triad-RED-S-related parameters.

CONCLUSION

High-level Kenyan male and female runners had low daily EI, but no tendency toward a higher prevalence of low BMD, or Triad-RED-S-related hormonal abnormalities. The occurrence of low EI was not a major risk factor in our athletes; this calls into question whether the current criteria for Triad-RED-S are entirely applicable for athletes of African ethnicity.

Relationship between Step Characteristics and Race Performance during 5000-m Race

This study examined the relationship between step characteristics and race time in a 5000-m race. Twenty-one male Japanese endurance runners performed a 5000-m race. Step length, step frequency, contact time, and flight time of two gait cycles (i.e., four consecutive ground contacts) were measured every 400-m by using high-speed video image. Moreover, step length was normalized to body height to minimize the effect of body size. In addition to step characteristics on each lap, the averages of all laps and the per cent change from the first half to the second half were calculated. The average step frequency and step length normalized to body height correlated significantly with the 5000-m race time (r = −0.611, r = −0.575, respectively, p < 0.05 for both). Per cent changes in contact time and step length correlated significantly with the 5000-m race time (r = 0.514, r = −0.486, respectively, p < 0.05 for both). These findings suggest that, in addition to higher step frequency and step length normalized to body height, smaller changes in step length during a given race may be an important step characteristic to achieving superior race performance in endurance runners.

Relationship between Biological, Training, and Physical Fitness Variables in the Expression of Performance in Non-Professional Runners

Sports performance is a multifactorial trait that can be associated with individual and environmental characteristics. In this study, the sample comprised 35 male runners, enrolled in the "InTrack" project. Information regarding variables related to runners' training was obtained via an online questionnaire, while anthropometric and body composition variables, as well as physical fitness components (muscular power, isometric strength, local muscular endurance, agility, and aerobic capacity) were measured, and a global physical fitness score (based on physical fitness components measured) was computed. The Weltman test (3200 m) was used to estimate runners' pace and their stride frequency. Linear regression was used, taking the running pace as dependent variable. The final model, comprising biological, physical fitness, spatiotemporal, and training variables, explained 86% of the running performance variance. Muscular power (β = -1.02; 95% CI = (-1.69)-(-0.35)), abdominal muscle endurance (β = -4.81; 95% CI = (-7.52)-(-2.10)), isometric strength (β = -422.95; 95% CI = (-689.65)-(-156.25)), global physical fitness (β = 27.14; 95% CI = 9.52-45.03), and stride frequency (β = -2.99; 95% CI = (-4.29)-(-1.69)) were significantly associated with performance, meaning that better results in tests and increasing the stride frequency leads to better performance. Individual characteristics and physical fitness components were demonstrated to be significant predictors for running performance.

Shorter Ground Contact Time and Better Running Economy: Evidence From Female Kenyan Runners

ABSTRACT

Mooses, M, Haile, DW, Ojiambo, R, Sang, M, Mooses, K, Lane, AR, and Hackney, AC. Shorter ground contact time and better running economy: evidence from female Kenyan runners. J Strength Cond Res 35(2): 481-486, 2021-Previously, it has been concluded that the improvement in running economy (RE) might be considered as a key to the continued improvement in performance when no further increase in V̇o2max is observed. To date, RE has been extensively studied among male East African distance runners. By contrast, there is a paucity of data on the RE of female East African runners. A total of 10 female Kenyan runners performed 3 × 1,600-m steady-state run trials on a flat outdoor clay track (400-m lap) at the intensities that corresponded to their everyday training intensities for easy, moderate, and fast running. Running economy together with gait characteristics was determined. Subjects showed moderate to very good RE at the first (202 ± 26 ml·kg-1·km-1) and second (188 ± 12 ml·kg-1·km-1) run trials, respectively. Correlation analysis revealed significant relationship between ground contact time (GCT) and RE at the second run (r = 0.782; p = 0.022), which represented the intensity of anaerobic threshold. This study is the first to report the RE and gait characteristics of East African female athletes measured under everyday training settings. We provided the evidence that GCT is associated with the superior RE of the female Kenyan runners.

Running Performance Variability among Runners from Different Brazilian States: A Multilevel Approach

The ecological model theory highlights that human development (or a given behavior) is the result of the interaction of variables derived from different levels, comprising those directly related to the subjects and those related to the environment. Given that, the purpose of this study is to establish whether runners' performance may vary among different Brazilian states, as the factors associated with this difference. The sample comprised 1151 Brazilian runners (61.8% men) that completed an online questionnaire, providing information about biological (sex, age, height, and weight), training (running pace, frequency and volume/week, and motivation), sociodemographic (place of residence and wage) aspects, and perceptions about the environmental influences on the practice. Information about state variables was obtained from official institutes, and comprised the human development index (HDI), athletics events, and violence index. Multilevel analysis was conducted in HLM software. State-level characteristics explained ≈3% of the total variance in running performance. Of the total variance explained for the individual level, 56.4% was associated with male sex (β = -54.98; p < 0.001), age (β = 1.09; p < 0.001), body mass index (β = 6.86; p < 0.001), economic status (β = 6.23; p = 0.003), the perception of the natural environment (β = 7.58; p = 0.02), training frequency (β = -16.64; p < 0.001), and weekly volume (β = -0.30; p < 0.001). At the state level, only athletics events presented a positive and significant influence on performance. There is a significant role of the environment on the explanation of running performance variability, and given the diversity across states, environmental variables should not be neglected, as they are relevant to the exploration of other variables possibly related to running performance.

Recent Improvements in Marathon Run Times Are Likely Technological, Not Physiological

Every women’s and men’s world records from 5 km to the marathon has been broken since the introduction of carbon fibre plate (CFP) shoes in 2016. This step-wise increase in performance coincides with recent advancements in shoe technology that increase the elastic properties of the shoe thereby reducing the energy cost of running. The latest CFP shoes are acknowledged to increase running economy by more than 4%, corresponding to a greater than 2% improvement in performance/run time. The recently modified rules governing competition shoes for elite athletes, announced by World Athletics, that includes sole thickness must not exceed 40 mm and must not contain more than one rigid embedded plate, appear contrary to the true essence and credibility of sport as access to this performance-defining technology becomes the primary differentiator of sporting performance in elite athletes. This is a particular problem in sports such as athletics where the primary sponsor of the athlete is very often a footwear manufacturing company. The postponement of the 2020 Summer Olympics provides a unique opportunity for reflection by the world of sport and time to commission an independent review to evaluate the impact of technology on the integrity of sporting competition. A potential solution to solve this issue can involve the reduction of the stack height of a shoe to 20 mm. This simple and practical solution would prevent shoe technology from having too large an impact on the energy cost of running and, therefore, determining the performance outcome.

Longer Achilles tendon moment arm results in better running economy

Based on the current literature, the link between Achilles tendon moment arm length and running economy is not well understood. Therefore, the aim of this study was to further investigate the connection between Achilles tendon moment arm and running economy and the influence of Achilles tendon moment arm on the function of the plantarflexor muscle-tendon unit during running.Ten male competitive marathon runners volunteered for this study. The participants ran on a treadmill at two running speeds: 3 and 3.5 m s-1. During running the oxygen consumption, lower leg kinematics, electrical activity of plantar flexor muscles, and fascicle behavior of the lateral gastrocnemius were measured simultaneously. On the second occasion, an MRI scan of the right leg was taken and used to estimate the Achilles tendon moment arm length.There was a negative correlation between running economy and the body height normalized moment arm length at both selected speeds (r = -0.68, P = 0.014 and r = -0.70, P = 0.01). In addition, Achilles tendon moment arm length correlated with the amplitude of the ankle flexion at both speeds (r = -0.59, P = 0.03 and r = -0.60, P = 0.03) and with the electrical activity of the medial gastrocnemius muscle at 3 m s-1 speed (r = -0.62, P = 0.02). Our finding supports the concept that a longer moment arm could be beneficial for distance runners.

Absolute Reliability and Concurrent Validity of the Stryd System for the Assessment of Running Stride Kinematics at Different Velocities

ABSTRACT

García-Pinillos, F, Roche-Seruendo, LE, Marcen-Cinca, N, Marco-Contreras, LA, and Latorre-Román, PA. Absolute reliability and concurrent validity of the Stryd system for the assessment of running stride kinematics at different velocities. J Strength Cond Res 35(1): 78-84, 2021-This study aimed to determine the absolute reliability and to evaluate the concurrent validity of the Stryd system for measuring spatiotemporal variables during running at different velocities (8-20 km·h-1) by comparing data with another widely used device (the OptoGait system). Eighteen trained male endurance runners performed an incremental running test (8-20 km·h-1 with 3-minute stages) on a treadmill. Spatiotemporal parameters (contact time [CT], flight time [FT], step length [SL], and step frequency [SF]) were measured using 2 different devices (Stryd and OptoGait systems). The Stryd system showed a coefficient of variation (CV) <3%, except for FT (3.7-11.6%). The OptoGait achieved CV <4%, except for FT (6.0-30.6%). Pearson correlation analysis showed large correlations for CT and FT, and almost perfect for SL and SF over the entire protocol. The intraclass correlation coefficients partially support those results. Paired t-tests showed that CT was underestimated (p < 0.05, effect size [ES] > 0.7; ∼4-8%), FT overestimated (p < 0.05, ES > 0.7; ∼7-65%), whereas SL and SF were very similar between systems (ES < 0.1, with differences <1%). The Stryd is a practical portable device that is reliable for measuring CT, FT, SL, and SF during running. It provides accurate SL and SF measures but underestimates CT (0.5-8%) and overestimates FT (3-67%) compared with a photocell-based system.

Calcaneus height is a key morphological factor of sprint performance in sprinters

This study examined the relationships between the foot bone morphologies and sprint performance in sprinters. Foot images in 56 male sprinters obtained using magnetic resonance imaging. The relative lengths of the forefoot bones of the big and second toes, which were calculated as total lengths of the forefoot bones for each toe normalized to the foot length, correlated significantly with personal best 100-m sprint time (r =  − 0.293 and − 0.459, both Ps < 0.05). The relative lengths of the rearfoot talus and calcaneus normalized to the foot length also correlated significantly with the sprint performance (r =  − 0.378 and − 0.496, both Ps < 0.05). Furthermore, the relative height of the calcaneus, but not the talus, normalized to body height correlated significantly with sprint performance (r =  − 0.690, P < 0.001). Additionally, the relative calcaneus height correlated significantly with the foot arch height index (r = 0.420, P = 0.001), and the foot arch height index correlated significantly with sprint performance (r =  − 0.517, P < 0.001). These findings suggest that the taller calcaneus may be a key morphological factor for achieving superior sprint performance, potentially via modeling the longer forefoot and rearfoot bones and functional foot morphology in sprinters.

The Effect of Different Cadence on Paddling Gross Efficiency and Economy in Stand-Up Paddle Boarding

Background: Due to the importance of energy efficiency and economy in endurance performance, it is important to know the influence of different paddling cadences on these variables in the stand-up paddleboarding (SUP). The purpose of this study was to determine the effect of paddling at different cadences on the energy efficiency, economy, and physiological variables of international SUP race competitors. Methods: Ten male paddlers (age 28.8 ± 11.0 years; height 175.4 ± 5.1 m; body mass 74.2 ± 9.4 kg) participating in international tests carried out two test sessions. In the first one, an incremental exercise test was conducted to assess maximal oxygen uptake and peak power output (PPO). On the second day, they underwent 3 trials of 8 min each at 75% of PPO reached in the first test session. Three cadences were carried out in different trials randomly assigned between 45–55 and 65 strokes-min⁻¹ (spm). Heart rate (HR), blood lactate, perceived sense of exertion (RPE), gross efficiency, economy, and oxygen uptake (VO₂) were measured in the middle (4-min) and the end (8-min) of each trial. Results: Economy (45.3 ± 5.7 KJ·l⁻¹ at 45 spm vs. 38.1 ± 5.3 KJ·l⁻¹ at 65 spm; p = 0.010) and gross efficiency (13.4 ± 2.3% at 45 spm vs. 11.0 ± 1.6% at 65 spm; p = 0.012) was higher during de 45 spm condition than 65 spm in the 8-min. Respiratory exchange ratio (RER) presented a lower value at 4-min than at 8-min in 55 spm (4-min, 0.950 ± 0.065 vs. 8-min, 0.964 ± 0.053) and 65 spm cadences (4-min, 0.951 ± 0.030 vs. 8-min, 0.992 ± 0.047; p < 0.05). VO₂, HR, lactate, and RPE were lower (p < 0.05) at 45 spm (VO₂, 34.4 ± 6.0 mL·kg⁻¹·min⁻¹; HR, 161.2 ± 16.4 beats·min⁻¹; lactate, 3.5 ± 1.0 mmol·l⁻¹; RPE, 6.0 ± 2.1) than at 55 spm (VO₂, 38.6 ± 5.2 mL·kg⁻¹·min⁻¹; HR, 168.1 ± 15.1 beats·min⁻¹; lactate, 4.2 ± 1.2 mmol·l⁻¹; RPE, 6.9 ± 1.4) and 65 spm (VO₂, 38.7 ± 5.9 mL·kg⁻¹·min⁻¹; HR, 170.7 ± 13.0 beats·min⁻¹; 5.3 ± 1.8 mmol·l⁻¹; RPE, 7.6 ± 1.4) at 8-min. Moreover, lactate and RPE at 65 spm was greater than 55 spm (p < 0.05) at 8-min. Conclusion: International male SUP paddlers were most efficient and economical when paddling at 45 spm vs. 55 or 65 spm, confirmed by lower RPE values, which may likely translate to faster paddling speed and greater endurance.

A pilot study on a potential relationship between leg bone length and sprint performance in sprinters; are there any event-related differences in 100-m and 400-m sprints?

OBJECTIVE

This study examined the relationship between leg bone length and sprint performance in sprinters. The leg bone lengths in 28 100-m specialized sprinters and 28 400-m specialized sprinters were measured using magnetic resonance imaging. The lengths of the upper and lower leg bones were assessed by calculating the lengths of the femur and tibia, respectively. To minimize differences in body size among participants, both bone lengths were normalized to body height. The ratio of the tibial length to femoral length was calculated to evaluate the interaction between the lengths of the upper and lower leg bones. International Amateur Athletic Federation (IAAF) scores, based on the personal best times of the sprinters in each group were used as parameters for sprint performance.

RESULTS

There were no significant correlations between absolute and relative lengths of the femur and tibia and IAAF scores in both 100-m and 400-m sprinters. By contrast, the ratio of the tibial length to femoral length correlated significantly with IAAF score in 400-m sprinters (r = 0.445, P = 0.018), but not 100-m sprinters. These findings suggest that the leg bone lengths may play an important role in achieving superior long sprint performance in 400-m specialized sprinters.

The Potential Relationship Between Leg Bone Length and Running Performance in Well-Trained Endurance Runners

The present study aimed to determine the relationship between leg bone length and running performance in well-trained endurance runners. The lengths of the leg bones in 42 male endurance runners (age: 20.0 ± 1.0 years, body height: 169.6 ± 5.6 cm, body mass: 56.4 ± 5.1 kg, personal best 5000-m race time: 14 min 59 s ± 28 s) were measured using magnetic resonance imaging. The lengths of the femur and tibia were calculated to assess the upper and lower leg lengths, respectively. The total length of the femur + tibia was calculated to assess the overall leg bone length. These lengths of the leg bones were normalized with body height, which was measured using a stadiometer to minimize differences in body size among participants. The relative tibial length was significantly correlated with personal best 5000-m race time (r = -0.328, p = 0.034). Moreover, a trend towards significance was observed in the relative femoral length (r = -0.301, p = 0.053). Furthermore, the relative total lengths of the femur + tibia were significantly correlated with personal best 5000-m race time (r = -0.353, p < 0.05). These findings suggest that although the relationship between the leg bone length and personal best 5000-m race time was relatively minor, the leg bone length, especially of the tibia, may be a potential morphological factor for achieving superior running performance in well-trained endurance runners.

Better Economy on Indoor Track Compared to Treadmill Running With 1% Inclination

Purpose: The purpose of this study was to investigate the differences in metabolic responses between the track and the treadmill (1% inclination) running. The latter is recommended for use in laboratory settings to mimic outdoor running. Method: Seventeen male endurance athletes (mean 25.8, s = 3.8 years) performed 4-min running bouts on an indoor track and the treadmill. Results: At all speeds (11, 13, and 15 km·h^-1) athletes showed better economy on the track running compared to the treadmill expressed as oxygen (7.9%, 5.2%, and 2.8%) and caloric (7.0%, 5.3%, and 2.6%) unit cost. Rating of perceived exertion was evaluated substantially higher at all speeds on the treadmill (F(1,16) = 31.45, p < .001, η²_p = .663) compared to running on the track. Participants presented lower heart rate (F(1,16) = 13.74, p = .002, η²_p = .462) on the track at the speed of 11 and 13 km·h^-1 compared to the treadmill, but not at 15 km·h^-1 (p = .021). Conclusions: We conclude that constant inclination (i.e.. 1%) during the treadmill test might not be suitable to reproduce comparable effort to running on the track; rather, there is an optimal treadmill inclination for different intensities to reproduce similar effort compared to the track running.

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.

How does the slope gradient affect spatiotemporal parameters during running? Influence of athletic level and vertical and leg stiffness

BACKGROUND

The current evidence leaves certain questions unanswered, including whether well-trained athletes adapt to different slope gradients in the same way as amateurs, and whether stiffness influences spatiotemporal adaptations during uphill running.

RESEARCH QUESTION

This study aimed to determine the effect of different slope gradients (0%-11%) on spatiotemporal gait characteristics during running, taking into account the influence of athletic level, vertical and leg stiffness.

METHODS

Male endurance runners (12 amateurs, 10 highly-trained) performed a running test on a motorized treadmill. The running velocity was set at 12 km/h, and participants completed six different running conditions (0, 3, 5, 7, 9 and 11% gradients). Spatiotemporal parameters were measured using the OptoGait system. Vertical (Kvert) and leg (Kleg) stiffness were calculated according to the sine-wave method.

RESULTS

A 2 (amateur; highly-trained) × 6 (running conditions) ANOVA found no significant between-group differences in spatiotemporal parameters at any gradient (P ≥ 0.05); however, significant Kvert and Kleg differences (P < 0.05) were found within both groups with increasing gradients. Stepwise linear regression analysis showed that Kleg was strongly associated with contact time (R²  = 0.797, P < 0.001), whereas Kvert was associated with spatiotemporal adaptations to different slope gradients (R²  = 0.547, P = 0.002).

SIGNIFICANCE

An increased slope gradient (0-11%) at a given running velocity (12 km.h^-1) caused spatiotemporal adaptations (i.e., increased CT and SF and decreased FT, SL and SA) regardless of the athletic level of the runner, although a non-significant trend differentiated the adaptations between the amateur and highly-trained groups. The results also indicated that leg stiffness plays a key role in the characteristics of spatiotemporal gait during level running, whereas vertical stiffness is strongly associated with spatiotemporal adaptations when running uphill.

Short Trail Running Race: Beyond the Classic Model for Endurance Running Performance

PURPOSE

This study aimed to examine the extent to which the classical physiological variables of endurance running performance (maximal oxygen uptake (V˙O2max), %V˙O2max at ventilatory threshold (VT), and running economy (RE)) but also muscle strength factors contribute to short trail running (TR) performance.

METHODS

A homogeneous group of nine highly trained trail runners performed an official TR race (27 km) and laboratory-based sessions to determine V˙O2max, %V˙O2max at VT, level RE (RE0%) and RE on a +10% slope, maximal voluntary concentric and eccentric knee extension torques, local endurance assessed by a fatigue index (FI), and a time to exhaustion at 87.5% of the velocity associated with V˙O2max. A simple regression method and commonality analysis identifying unique and common coefficients of each independent variable were used to determine the best predictors for the TR race time (dependent variable).

RESULTS

Pearson correlations showed that FI and V˙O2max had the highest correlations (r = 0.91 and r = -0.76, respectively) with TR performance. The other selected variables were not significantly correlated with TR performance. The analysis of unique and common coefficients of relative V˙O2max, %V˙O2max at VT, and RE0% provides a low prediction of TR performance (R = 0.48). However, adding FI and RE on a +10% slope (instead of RE0%) markedly improved the predictive power of the model (R = 0.98). FI and V˙O2max showed the highest unique (49.8% and 20.4% of total effect, respectively) and common (26.9% of total effect) contributions to the regression equation.

CONCLUSIONS

The classic endurance running model does not allow for meaningful prediction of short TR performance. Incorporating more specific factors into TR such as local endurance and gradient-specific RE testing procedures should be considered to better characterize short TR performance.

Running Performance, VO2max, and Running Economy: The Widespread Issue of Endogenous Selection Bias

Studies in sport and exercise medicine routinely use samples of highly trained individuals in order to understand what characterizes elite endurance performance, such as running economy and maximal oxygen uptake VO_2max. However, it is not well understood in the literature that using such samples most certainly leads to biased findings and accordingly potentially erroneous conclusions because of endogenous selection bias. In this paper, I review the current literature on running economy and VO_2max, and discuss the literature in light of endogenous selection bias. I demonstrate that the results in a large part of the literature may be misleading, and provide some practical suggestions as to how future studies may alleviate endogenous selection bias.

Lack of Influence of Muscular Performance Parameters on Spatiotemporal Adaptations With Increased Running Velocity

Roche-Seruendo, LE, García-Pinillos, F, Haicaguerre, J, Bataller-Cervero, AV, Soto-Hermoso, VM, and Latorre-Román, PÁ. Lack of influence of muscular performance parameters on spatiotemporal adaptations with increased running velocity. J Strength Cond Res 32(2): 409-415, 2018-This study aimed to analyze the influence of muscular performance parameters on spatiotemporal gait characteristics during running when gradually increasing speed. Fifty-one recreationally trained male endurance runners (age, 28 ± 8 years) voluntarily participated in this study. Subjects performed a battery of jumping tests (squat jump, countermovement jump, and 20-cm drop jump), and after that, the subjects performed an incremental running test (10-20 km·h) on a motorized treadmill. Spatiotemporal parameters were measured using the OptoGait system. Cluster k-means analysis grouped subjects according to the jumping test performance, by obtaining a group of good jumpers (n = 19) and a group of bad jumpers (n = 32). With increased running velocity, contact time was shorter and flight time and step length were longer, whereas cadence and stride angle were greater (p < 0.001). No significant differences between groups (p ≥ 0.05) were found at any running speed. The results obtained indicate that increased running velocity produced no differences in spatiotemporal adaptations between those runners with good jumping ability and those with poor jumping ability. Based on that, it seems that muscular performance parameters do not play a key role in spatiotemporal adaptations experienced by recreational endurance runners with increased velocity. However, taken into consideration the well-known relationship between running performance and neuromuscular performance, the authors suggest that muscular performance parameters would be much more determinant in the presence of fatigue (exhausted condition) or in the case of considering other variables such as running economy or kinetic.

Differences in Spatiotemporal Parameters Between Trained Runners and Untrained Participants

Gómez-Molina, J, Ogueta-Alday, A, Stickley, C, Tobalina, JC, Cabrejas-Ugartondo, J, and García-López, J. Differences in spatiotemporal parameters between trained runners and untrained participants. J Strength Cond Res 31(8): 2169-2175, 2017-The aim of this study was to compare the spatiotemporal parameters of trained runners and untrained participants with the same foot strike pattern (rearfoot) during running at controlled speeds. Twenty-one participants were classified in 2 groups according to their training experience: Trained (n = 10, amateur runners with long distance training experience) and Untrained (n = 11, healthy untrained participants). Anthropometric variables were recorded, and the participants performed both a submaximal (between 9 and 15 km·h) and a graded exercise running test (from 6 km·h until exhaustion) on a treadmill. Physiological (V[Combining Dot Above]O2max, heart rate, running economy [RE], peak speed …) and biomechanical variables (contact and flight times, step rate, and length) were simultaneously registered. Trained runners showed higher step rate and shorter step length than the Untrained group at the same running speeds (between 4 and 7%, p ≤ 0.05) and at the same physiological intensities (between 7 and 11%, p ≤ 0.05). However, there were no differences in contact and flight times between groups. Significant differences (p ≤ 0.05) and large effect sizes (Cohen's d) between groups were found for body mass, sum of 6 skinfolds, V[Combining Dot Above]O2max, peak speed, and ventilatory threshold and respiratory compensation threshold speeds. The Trained group also showed a ∼7% better RE (ml·kg·km) than the Untrained group. In conclusion, adopting higher step rate and shorter step length may be an adaptive mechanism of the Trained group to reduce injury risk and possibly improve RE. However, contact and flight times were consistent regardless of training level.

Similarities and differences among half-marathon runners according to their performance level

This study aimed to identify the similarities and differences among half-marathon runners in relation to their performance level. Forty-eight male runners were classified into 4 groups according to their performance level in a half-marathon (min): Group 1 (n = 11, < 70 min), Group 2 (n = 13, < 80 min), Group 3 (n = 13, < 90 min), Group 4 (n = 11, < 105 min). In two separate sessions, training-related, anthropometric, physiological, foot strike pattern and spatio-temporal variables were recorded. Significant differences (p<0.05) between groups (ES = 0.55–3.16) and correlations with performance were obtained (r = 0.34–0.92) in training-related (experience and running distance per week), anthropometric (mass, body mass index and sum of 6 skinfolds), physiological (VO_2max, RCT and running economy), foot strike pattern and spatio-temporal variables (contact time, step rate and length). At standardized submaximal speeds (11, 13 and 15 km·h^-1), no significant differences between groups were observed in step rate and length, neither in contact time when foot strike pattern was taken into account. In conclusion, apart from training-related, anthropometric and physiological variables, foot strike pattern and step length were the only biomechanical variables sensitive to half-marathon performance, which are essential to achieve high running speeds. However, when foot strike pattern and running speeds were controlled (submaximal test), the spatio-temporal variables were similar. This indicates that foot strike pattern and running speed are responsible for spatio-temporal differences among runners of different performance level.

Does Foot Anthropometry Predict Metabolic Cost During Running?

Several recent investigations have linked running economy to heel length, with shorter heels being associated with less metabolic energy consumption. It has been hypothesized that shorter heels require larger plantar flexor muscle forces, thus increasing tendon energy storage and reducing metabolic cost. The goal of this study was to investigate this possible mechanism for metabolic cost reduction. Fifteen male subjects ran at 16 km⋅h^-1 on a treadmill and subsequently on a force-plate instrumented runway. Measurements of oxygen consumption, kinematics, and ground reaction forces were collected. Correlational analyses were performed between oxygen consumption and anthropometric and kinetic variables associated with the ankle and foot. Correlations were also computed between kinetic variables (peak joint moment and peak tendon force) and heel length. Estimated peak Achilles tendon force normalized to body weight was found to be strongly correlated with heel length normalized to body height (r = -.751, p = .003). Neither heel length nor any other measured or calculated variable were correlated with oxygen consumption, however. Subjects with shorter heels experienced larger Achilles tendon forces, but these forces were not associated with reduced metabolic cost. No other anthropometric and kinetic variables considered explained the variance in metabolic cost across individuals.

Lower Leg Length is Associated with Running Economy in High Level Caucasian Distance Runners

The aim of the present study was to investigate lower limb anthropometric and composition variables related to running economy (RE) and running performance in a homogeneous group of high level European distance runners. RE at the speeds of 14, 16 and 18 km·h⁻¹ (189 ± 12; 188 ± 11; 187 ± 11 O₂ ml·kg⁻¹·km⁻¹) and maximal oxygen uptake (VO_2max) (67.3 ± 2.9 ml·kg⁻¹·min⁻¹) of 13 high level distance runners were determined on a motorised treadmill. Anthropometric variables and body composition were measured. The BMI was related to RE at the speed of 14 (r² = 0.434; p = 0.014), 16 (r² = 0.436; p = 0.014) and 18 km·h⁻¹ (r² = 0.389; p = 0.023). Lower leg length was negatively related to RE at the speed of 16 and showed such a tendency at the speed of 14 and 18 km·h⁻¹. VO_2max indicated a moderate relationship with RE at the speeds of 14, 16 and 18 km·h⁻¹ (r² = 0.372, p = 0.030; r² = 0.350, p = 0.033; r² = 0.376, p = 0.026, respectively) which was confirmed by subsequent partial correlation analysis. While lower leg length and the BMI presented a relationship with RE, none of the calculated body composition and anthropometric proportions were related to RE or performance. The relationship between RE and VO_2max would confirm the notion that RE could be at least partly compensated by VO_2max to achieve high performance results.

Bone health in elite Kenyan runners

Impact loading in athletes participating in various sports has been positively associated with increased bone mineral density (BMD), but this has not been investigated in elite Kenyan runners. Body composition and site-specific BMD measures quantified with dual x-ray absorptiometry were measured in 15 elite male Kenyan runners and 23 apparently healthy South African males of different ethnicities. Training load and biomechanical variables associated with impact loading, such as joint stiffness, were determined in the elite Kenyan runners. Greater proximal femur (PF) BMD (g · cm^-2) was higher (P = 0.001, ES = 1.24) in the elite Kenyan runners compared with the controls. Six of the 15 (40%) Kenyan runners exhibited lumbar spine (LS) Z-Scores below -2.0 SD, whereas this was not found in the apparently healthy controls. PFBMD was associated with training load (r = 0.560, P = 0.003) and ankle (r = 0.710, P = 0.004) and knee (r = 0.546, P = 0.043) joint stiffness. Elite Kenyan runners exhibit greater PFBMD than healthy controls, which is associated with higher training load and higher joint stiffness. Our results reaffirm the benefits of impact loading on BMD at a weight-bearing site, while a high prevalence of low LSBMD in the elite Kenyan runners is hypothesised to be the result of a mismatch between energy intake and high training load. Future research investigating energy availability in Kenyan runners and the possible association with musculoskeletal injury should be investigated.

Foot structure is correlated with performance in a single-joint jumping task

Variability in musculoskeletal structure has the potential to influence locomotor function. It has been shown, for example, that sprinters have smaller Achilles tendon moment arms and longer toes than non-sprinters, and toe length has been found to correlate with toe flexor work in running humans. These findings suggest that interindividual variation in human foot structure allows for function that is adapted to various motor tasks. The purpose of this study was to test for correlations between foot anthropometry and single-joint maximal-height jumping performance. Ten male subjects performed static jumps using only their ankles for propulsion. Several anthropometric measures were taken. Bivariate correlation analyses were performed between all anthropometric variables and the average jump height for each subject. Results showed that the best jumpers had longer lateral heel lengths (r=0.871; p=0.001) and longer toes (r=0.712; p=0.021). None of the other anthropometric variables (stature, mass, lower extremity lengths) measured were found to correlate significantly with jump height. A factor analysis was performed to investigate whether some underlying feature related to body stature could explain jumping performance. Taller subjects did not necessarily jump higher. Specific variations in foot structure, unrelated to other general stature measures, were associated with performance in this single-joint jumping task.

The Kenyan runners

Today the Kenyan dominance in middle- and long-distance running is so profound that it has no equivalence to any other sport in the world. Critical physiological factors for performance in running include maximal oxygen consumption (VO2max), fractional VO2max utilization and running economy (energetic cost of running). Kenyan and non-Kenyan elite runners seem to be able to reach very high, but similar maximal oxygen uptake levels just as there is some indication that untrained Kenyans and non-Kenyans have a similar VO2max. In addition, the fractional utilization of VO2max seems to be very high but similar in Kenyan and European runners. Similarly, no differences in the proportion of slow muscle fibers have been observed when comparing Kenyan elite runners with their Caucasian counterparts. In contrast, the oxygen cost of running at a given running velocity has been found to be lower in Kenyan elite runners relative to other elite runners and there is some indication that this is due to differences in body dimensions. Pulmonary system limitations have been observed in Kenyan runners in the form of exercise-induced arterial hypoxemia, expiratory flow limitation, and high levels of respiratory muscle work. It appears that Kenyan runners do not possess a pulmonary system that confers a physiological advantage. Additional studies on truly elite Kenyan runners are necessary to understand the underlying physiology which permits extraordinary running performances.

Are gait characteristics and ground reaction forces related to energy cost of running in elite Kenyan runners?

The aim of this study was to determine whether gait cycle characteristics are associated with running economy in elite Kenyan runners. Fifteen elite Kenyan male runners completed two constant-speed running sets on a treadmill (12 km ·h^-1 and 20 km ·h^-1). VO₂ and respiratory exchange ratio values were measured to calculate steady-state oxygen and energy cost of running. Gait cycle characteristics and ground contact forces were measured at each speed. Oxygen cost of running at different velocities was 192.2 ± 14.7 ml· kg^-1· km^-1 at 12 km· h^-1 and 184.8 ± 9.9 ml· kg^-1· km^-1 at 20 km· h^-1, which corresponded to a caloric cost of running of 0.94 ± 0.07 kcal ·kg^-1·km^-1 and 0.93 ± 0.07 kcal· kg^-1· km^-1. We found no significant correlations between oxygen and energy cost of running and biomechanical variables and ground reaction forces at either 12 or 20 km· h^-1. However, ground contact times were ~10.0% shorter (very large effect) than in previously published literature in elite runners at similar speeds, alongside an 8.9% lower oxygen cost (very large effect). These results provide evidence to hypothesise that the short ground contact times may contribute to the exceptional running economy of Kenyan runners.

Letter to the editor

Santos-Concejero and Tucker argued in their letter to the editor that in our study the running economy in achieving superior performance was overlooked due to some methodological aspects. Having given the remarks of Santos-Concejero and Tucker appropriate consideration, in this letter to the editor, we argue that our paper does not downplay the influence of running economy on the determinants of the East African running phenomenon, but rather adds novel insights into the interaction between running economy, maximal oxygen uptake and performance.

Better economy in field running than on the treadmill: evidence from high-level distance runners

Given the ongoing interest in ways to improve the specificity of testing elite athletes in their natural environment, portable metabolic systems provide an opportunity to assess metabolic demand of exercise in sport-specific settings. Running economy (RE) and maximal oxygen uptake ([Formula: see text]O2max) were compared between track and treadmill (1% inclination) conditions in competitive level European distance runners who were fully habituated to treadmill running (n = 13). All runners performed an exercise test on running track and on treadmill. While [Formula: see text]O2max was similar on the track and on the treadmill (68.5 ± 5.3 vs. 71.4 ± 6.4 ml·kg(-1)·min(-1), p = 0.105, respectively), superior RE was found on the track compared to the treadmill (215.4 ± 12.4 vs. 236.8 ± 18.0 O2 ml·kg(-1)·km(-1), p < 0.001). RE on the track was strongly correlated with RE on the treadmill (r = 0.719, p = 0.006). The present findings indicate that high-level distance runners have significantly better RE but not [Formula: see text]O2max on the track compared to treadmill. This difference may be due to biomechanical adjustments. As RE is strongly correlated between the two conditions, it would be reasonable to assume that interventions affecting RE on the treadmill will also affect RE on the track.