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How muscles maximize performance in accelerated sprinting

DOI:10.1111/sms.14021
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Marcus G. Pandy
Marcus G. Pandy
Marcus G. Pandy
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Adrian Lai at lululemon
Adrian Lai
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Anthony G. Schache
Anthony G. Schache
Anthony G. Schache
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Yi-Chung Lin at Australian Catholic University
Yi-Chung Lin
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Abstract and Figures

We sought to provide a more comprehensive understanding of how the individual leg muscles act synergistically to generate a ground force impulse and maximize the change in forward momentum of the body during accelerated sprinting. We combined musculoskeletal modelling with gait data to simulate the majority of the acceleration phase (19 foot contacts) of a maximal sprint over ground. Individual muscle contributions to the ground force impulse were found by evaluating each muscle’s contribution to the vertical and fore-aft components of the ground force (termed ‘supporter’ and ‘accelerator/brake’, respectively). The ankle plantarflexors played a major role in achieving maximal-effort accelerated sprinting. Soleus acted primarily as a supporter by generating a large fraction of the upward impulse at each step whereas gastrocnemius contributed appreciably to the propulsive and upward impulses and functioned as both accelerator and supporter. The primary role of the vasti was to deliver an upward impulse to the body (supporter), but these muscles also acted as a brake by retarding forward momentum. The hamstrings and gluteus medius functioned primarily as accelerators. Gluteus maximus was neither an accelerator nor supporter as it functioned mainly to decelerate the swinging leg in preparation for foot contact at the next step. Fundamental knowledge of lower-limb muscle function during maximum acceleration sprinting is of interest to coaches endeavouring to optimize sprint performance in elite athletes as well as sports medicine clinicians aiming to improve injury prevention and rehabilitation practices.
Time histories of the forces calculated for representative muscles at the 1st, 7th and 19th foot contacts (FC1, FC7 and FC19) of the acceleration phase of sprinting. The solid lines represent mean muscle forces for all participants and the shaded areas represent +1 standard deviation from the mean. Muscle forces were normalized by each participant's body weight (BW). Muscle symbols are: ILIOPSOAS, iliacus and psoas combined; GMAX, superior, middle, inferior portions of gluteus maximus combined; GMED, anterior and posterior portions of gluteus medius/minimus combined; HAMS, semimembranosus, semitendinosus, and biceps femoris long head and short head combined; RF, rectus femoris; VAS, vastus medialis, intermedius, and lateralis combined; SOL, soleus; GAS, medial and lateral gastrocnemius combined. Results shown are for the ipsilateral limb
Time histories of the forces calculated for representative muscles at the 1st, 7th and 19th foot contacts (FC1, FC7 and FC19) of the acceleration phase of sprinting. The solid lines represent mean muscle forces for all participants and the shaded areas represent +1 standard deviation from the mean. Muscle forces were normalized by each participant's body weight (BW). Muscle symbols are: ILIOPSOAS, iliacus and psoas combined; GMAX, superior, middle, inferior portions of gluteus maximus combined; GMED, anterior and posterior portions of gluteus medius/minimus combined; HAMS, semimembranosus, semitendinosus, and biceps femoris long head and short head combined; RF, rectus femoris; VAS, vastus medialis, intermedius, and lateralis combined; SOL, soleus; GAS, medial and lateral gastrocnemius combined. Results shown are for the ipsilateral limb
… 
Contributions of individual muscles to the net joint moments exerted about the hip, knee, and ankle for the 1st, 7th and 19th foot contacts (FC1, FC7 and FC19). Moments were normalized by each participant's body mass and averaged across all participants. The shaded regions represent the net joint moments calculated from the experimental gait data using inverse dynamics while the dashed lines are the model‐predicted moments obtained by taking the product of muscle force and moment arm and summing across all the muscles spanning each joint. Hip extension, knee extension and ankle plantarflexion moments are positive. Muscle symbols are defined in Figure 1
Contributions of individual muscles to the net joint moments exerted about the hip, knee, and ankle for the 1st, 7th and 19th foot contacts (FC1, FC7 and FC19). Moments were normalized by each participant's body mass and averaged across all participants. The shaded regions represent the net joint moments calculated from the experimental gait data using inverse dynamics while the dashed lines are the model‐predicted moments obtained by taking the product of muscle force and moment arm and summing across all the muscles spanning each joint. Hip extension, knee extension and ankle plantarflexion moments are positive. Muscle symbols are defined in Figure 1
… 
Contributions of individual muscles to the fore‐aft (A, top two rows) and vertical (B, bottom two rows) components of the GRF for the 1st, 7th and 19th foot contacts (FC1, FC7 and FC19). GRFs were normalized by each participant's body weight (BW) and averaged across all participants. The shaded regions represent the force plate measurements obtained at each foot contact. Muscle symbols are defined in Figure 1
Contributions of individual muscles to the fore‐aft (A, top two rows) and vertical (B, bottom two rows) components of the GRF for the 1st, 7th and 19th foot contacts (FC1, FC7 and FC19). GRFs were normalized by each participant's body weight (BW) and averaged across all participants. The shaded regions represent the force plate measurements obtained at each foot contact. Muscle symbols are defined in Figure 1
… 
Potential muscle contributions to the fore‐aft (A) and vertical (B) GRF impulses for the first 19 foot contacts of the acceleration phase of sprinting. The potential contribution of a muscle to the GRF impulse represents the effect of a unit of force (1.0 N) applied by that muscle in isolation, with all other muscle forces assumed to be zero at that instant. Potential muscle contributions to the GRF impulse were normalized by body mass and averaged across all participants. Muscle symbols are defined in Figure 1
Potential muscle contributions to the fore‐aft (A) and vertical (B) GRF impulses for the first 19 foot contacts of the acceleration phase of sprinting. The potential contribution of a muscle to the GRF impulse represents the effect of a unit of force (1.0 N) applied by that muscle in isolation, with all other muscle forces assumed to be zero at that instant. Potential muscle contributions to the GRF impulse were normalized by body mass and averaged across all participants. Muscle symbols are defined in Figure 1
… 
Actual muscle contributions to the net fore‐aft (A) and vertical (B) GRF impulses for the first 19 foot contacts of the acceleration phase of sprinting. The actual contribution of a muscle considers the magnitude of force developed by that muscle at each instant of the simulated sprint. The top two rows show the muscle contributions to net fore‐aft (propulsive) and vertical (support) GRF impulses generated at each foot contact. The bottom row shows the percentage contributions of individual muscles to the total propulsive and support GRF impulses generated by all the muscles across all 19 foot contacts. Muscle contributions to the GRF impulse were normalized by body mass and averaged across all participants. Muscle symbols are defined in Figure 1
+1
Actual muscle contributions to the net fore‐aft (A) and vertical (B) GRF impulses for the first 19 foot contacts of the acceleration phase of sprinting. The actual contribution of a muscle considers the magnitude of force developed by that muscle at each instant of the simulated sprint. The top two rows show the muscle contributions to net fore‐aft (propulsive) and vertical (support) GRF impulses generated at each foot contact. The bottom row shows the percentage contributions of individual muscles to the total propulsive and support GRF impulses generated by all the muscles across all 19 foot contacts. Muscle contributions to the GRF impulse were normalized by body mass and averaged across all participants. Muscle symbols are defined in Figure 1
… 
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1882
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Scand J Med Sci Sports. 2021;31:1882–1896.
wileyonlinelibrary.com/journal/sms
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INTRODUCTION
The best sprinters run at an average speed of approximately
10 m/s and can reach maximum speeds of nearly 13 m/s
during a 100m race.1 This level of exceptional performance
is achieved by maximally accelerating the body during the
first half of the race and maintaining that momentum there-
after. The force generated on the ground at each foot contact
creates an impulse that causes the necessary increase in for-
ward momentum of the body's center of mass. The lower-
limb muscles together with the actions of gravity and inertia
generate the required ground force impulse, but the overall
contribution from the muscles is by far the greatest.2,3
Many investigators have performed inverse dynamics
analyses to determine the net moments exerted by the lower-
limb joints for sprinting at a steady- state speed.4- 6 Recent
studies also have estimated the forces developed by the leg
muscles for running at various steady- state speeds, including
sprinting.2,3,7 Soleus, gastrocnemius and vasti were found to
be the major contributors to the vertical (support) and fore-
aft (propulsive/braking) components of the ground reaction
force (GRF) at all steady- state running speeds.2,3
Received: 16 May 2021
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Revised: 1 July 2021
|
Accepted: 10 July 2021
DOI: 10.1111/sms.14021
ORIGINAL ARTICLE
How muscles maximize performance in accelerated sprinting
Marcus G.Pandy1
|
Adrian K. M.Lai2
|
Anthony G.Schache1,3
|
Yi- ChungLin1
© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
1Department of Mechanical Engineering,
University of Melbourne, Parkville,
Victoria, Australia
2Department of Biomedical Physiology
and Kinesiology, Simon Fraser
University, Burnaby, Canada
3La Trobe Sport and Exercise Medicine
Research Centre, La Trobe University,
Bundoora, Australia
Correspondence
Marcus G. Pandy, Department of
Mechanical Engineering, University of
Melbourne, Parkville, Victoria 3010,
Australia.
Email: pandym@unimelb.edu.au
Funding information
Australian Research Council, Grant/
Award Number: LP110100262
We sought to provide a more comprehensive understanding of how the individual
leg muscles act synergistically to generate a ground force impulse and maximize the
change in forward momentum of the body during accelerated sprinting. We combined
musculoskeletal modelling with gait data to simulate the majority of the acceleration
phase (19 foot contacts) of a maximal sprint over ground. Individual muscle contribu-
tions to the ground force impulse were found by evaluating each muscle's contribu-
tion to the vertical and fore- aft components of the ground force (termed “supporter”
and “accelerator/brake,” respectively). The ankle plantarflexors played a major role in
achieving maximal- effort accelerated sprinting. Soleus acted primarily as a supporter
by generating a large fraction of the upward impulse at each step whereas gastrocne-
mius contributed appreciably to the propulsive and upward impulses and functioned
as both accelerator and supporter. The primary role of the vasti was to deliver an
upward impulse to the body (supporter), but these muscles also acted as a brake by
retarding forward momentum. The hamstrings and gluteus medius functioned primar-
ily as accelerators. Gluteus maximus was neither an accelerator nor supporter as it
functioned mainly to decelerate the swinging leg in preparation for foot contact at the
next step. Fundamental knowledge of lower- limb muscle function during maximum
acceleration sprinting is of interest to coaches endeavoring to optimize sprint perfor-
mance in elite athletes as well as sports medicine clinicians aiming to improve injury
prevention and rehabilitation practices.
KEYWORDS
gluteal, hamstring, impulse, plantarflexor, propulsion, running
... A major synergistic muscle to support hip extension is the M. gluteus medius (Neumann, 2010), which has been described as an important generator of horizontal forces during accelerated sprinting 30 (Pandy et al., 2021). Therefore, it is imperative to improve his proper function to enhance accelerationspecific activation patterns. ...
How to activate the glutes best? Peak muscle activity of acceleration-specific pre-activation and traditional strength training exercises
Preprint
  • Mar 2023
ABSTRACT. Isometric training and pre-activation are proven to enhance acceleration performance. However, traditional strength training exercises do not mirror the acceleration-specific activation patterns of the gluteal muscles, characterized by ipsilateral hip extension during contralateral hip flexion. Therefore, peak electromyographic activity of two acceleration-specific exercises was investigated and compared to two traditional strength training exercises each for the M. gluteus maximus (GMAX) and medius (GMED). Twenty-four participants from various athletic backgrounds (13 males, 11 females, 26 years, 178 cm, 77 kg) performed four GMAX (half-kneeling glute squeeze (HKGS), resisted knee split (RKS), hip thrust (HT), split squat (SS)) and four GMED (resisted abduction in prone position (RAPP), isometric clam (IC), side-plank with leg abduction (SP), resisted side-stepping (RSS)) exercises in a randomized order. No significant differences (p>0.05) were found between the HT, RKS and HKGS. The RKS (p=0.011, d=0.96) and the HKGS (p=0.064, d=0.68) elicited higher peak activity than the SS with large and moderate effects, respectively. The RAPP elicited significantly higher GMED activity with large effect compared to RSS (p<0.001, d=1.41) and moderate effect concerning the SP(p=0.002, d=0.78). Consequently, the acceleration-specific exercises effectively activate the gluteal muscles for pre-activation and strength training purposes to improve horizontal acceleration.
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... In combination with increasing the required strength capacities of the 'accelerative' muscles (e.g., hamstrings, gluteus medius, gastrocnemii). 7 The fundamental aspects of linear acceleration ('ankle rocker', 'shin roll', 'scissor action' of the thighs and 'knee split') should be emphasized in both technical as well as in strength and conditioning training sessions (Fig. 4). They facilitate optimal muscle actions, energy transfer, and movement efficiency driven by well-timed reciprocal actions of the stance and swing leg. 3 Fig. 4. ...
"Shin roll" and its importance in acceleration - Sportsmith Six
Research
Full-text available
  • Sep 2022
https://www.sportsmith.co/articles/shin-roll-acceleration/
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... This suggests that at least at 30°, Maltese sprinters demonstrate comparatively strong hamstrings in relation to their quadriceps. This relatively high capacity for force production in the hamstrings, specifically, is not surprising when considering that the hamstrings are known to play a dominant role in the sprinting action (Morin et al., 2015;Pandy et al., 2021). Fousekis et al. (2010), meanwhile, made the argument that optimal ratios are more important in the dominant leg, but this was not evident in our findings. ...
A Study of Lower-limb Bilateral and Unilateral Strength Asymmetry in Maltese Sprinters using the Modified Sphygmomanometer Test
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In track and field athletics, sprint events require athletes to negotiate both straight as well as curved segments of the track. Athletes specializing in the longer sprints must thereby execute symmetrical as well as inherently asymmetrical movement patterns. Few studies have investigated lower-limb strength asymmetry in sprinters internationally, or indeed other factors related to the health and performance of sprinters in the specific case of Malta. This study aimed to explore the general state of affairs with regard to bilateral and unilateral strength asymmetries, specifically in Maltese sprinters, using the modified sphygmomanometer test as a convenient and low-cost method of assessment. We also tested a series of hypotheses investigating the effects on asymmetry of training age, running the curve and leg-dominance. The participants exhibited efficient hamstring to quadriceps strength ratios for sprinting, and generally stronger non-dominant hamstrings bilaterally. Running the curve and left-or right-leggedness did not have significant impacts on any form of lower-limb strength symmetry. There was some evidence to suggest that experienced sprinters may, to a limited degree, manage asymmetrical force production efficiently just where it matters the most. We also discuss the merits of sphygmomanometer testing in the context of purposive asymmetry-reducing neuromuscular control as a learned skill on the part of athletes and make recommendations for future research.
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... Furthermore, the hip extensor muscles have been identified as likely important contributors to horizontal GRF and sprint acceleration performance during early acceleration (Morin et al., 2015b;Pandy et al., 2021). Collectively, these findings suggest that the ability to produce large hip extensor moments and powers appear to be important for acceleration performance during the initial steps. ...
BIOMECHANICS AND MOTOR CONTROL OF EARLY ACCELERATION: ENHANCING THE INITIAL SPRINT PERFORMANCE OF PROFESSIONAL RUGBY UNION BACKS
Thesis
Full-text available
  • Oct 2022
Biomechanics and motor control of early acceleration: Enhancing the initial sprint performance of professional rugby union backs Sprint acceleration is an important performance feature in many sports. For professional rugby union backs, short distance sprints are frequently carried out in training and competition, but how technique and strength-based characteristics contribute to their acceleration performance during these initial steps is not currently well understood. A series of investigations were therefore undertaken to, firstly, advance the understanding of this area and, secondly, to apply this information by prescribing individual-specific interventions to enhance initial acceleration performance. Three initial investigations sought to determine how technical features and strength-based qualities of professional rugby union backs related to their sprint performance (quantified as normalised average horizontal external power) during the initial steps. Findings from these investigations highlighted that focussing on the contribution of discrete technical variables to acceleration performance in isolation is an overly reductionist approach which overlooks how complex systems achieve high sprint performance. Findings also highlighted how important information on individuals can be lost using group-based study designs, since different inter-athlete strategies were adopted to achieve similar performance outcomes. In the fourth investigation, four subgroups of participants were identified, using cluster analysis, based on their whole-body kinematic strategies. At the intra-individual level, the variables which portrayed their individual strategies remained stable (CV: 1.9% to 6.7%) across multiple separate occasions. This characterisation of whole-body strategies was used to develop a novel and rigorous approach to longitudinally assess the efficacy of technical-based acceleration interventions. Demonstrating the application of this approach in the final investigation, several individual-specific interventions were prescribed to professional rugby union backs based on within-individual relationships of their technique strategies and strength-based capabilities with acceleration performance. Changes in within-individual technique and acceleration performance were measured at multiple time points across an 18-week intervention period where meaningful enhancements in acceleration were observed. This demonstrated that individual-specific technical interventions were effective in manipulating aspects of acceleration technique and performance. The outcome of these investigations provides a novel approach for practitioners working to individualise sprint-based practices.
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... Decelerations have a higher mechanical load [31] that can inflict greater damage on soft-tissue structures especially if high-force impacts cannot be attenuated efficiently [32]. Consequently, these actions may contribute to induced muscle damage, reduced neural drive and mechanical fatigue with potential detrimental effects on performance outcomes [33][34][35][36]. Indeed, the current results lead to a better understanding of the mechanisms underlying why soccer players are fatigued and give insight into NMF which affects sprinting performance. ...
Match Loads May Predict Neuromuscular Fatigue and Intermittent-Running Endurance Capacity Decrement after a Soccer Match
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How the match-derived load metrics relate to post-match fatigue in soccer is scarcely researched. Thus, the aim of this study was to determine the associations between soccer match-related internal and external loads, neuromuscular performance decrease and intermittent-running endurance capacity decrement immediately post-match. Vertical jump (countermovement jump), straight-line sprinting (10- and 20-m sprint), change of direction ability (T-test) and intermittent-running endurance capacity (YO-YO intermittent recovery level 2) were measured one day before and immediately after a friendly match in male soccer players. During the match, players’ internal and external loads were also monitored, including heart rate-derived indices, total distance at various speed thresholds, average running velocity, maximal running velocity, number of sprints and number of accelerations and decelerations at various intensity thresholds. The results show that match-induced fatigue was reflected on neuromuscular performance and intermittent-running endurance capacity immediately post-match (p < 0.05). The quantification of percentage change of match external-load metrics, particularly accelerations and decelerations, provides a useful non-invasive predictor of subsequent neuromuscular fatigue status in soccer players immediately post-match (p < 0.05). However, only internal load metrics present a practical application for predicting intermittent-running endurance capacity impairment (p < 0.05). In summary, internal and external load metrics may allow for predicting the extent of acute fatigue, and variability between halves may represent a valuable alternative to facilitate the analysis of match-related fatigue both for research and applied purposes.
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... 25 The triceps surae muscle group has recently been shown to be an important contributor to force generation during propulsion tasks. 26 Just before the take-off, when the foot is planted in dorsiflexion, the calf muscle produces an eccentric contraction to prevent falling over the planted foot. At this time, energy is stored in the AT as elastic energy, which ultimately assists in propulsion in a stretchshortening cycle. ...
Video analysis of Achilles tendon rupture in male professional football (soccer) players: injury mechanisms, patterns and biomechanics
Article
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  • Sep 2022
Background Achilles tendon rupture (ATR), while rare in football, is a severe career-threatening injury associated with long-layoff times. To date, no study has documented ATR’s mechanism in professional football players. Aim To describe the mechanisms, situational patterns and gross biomechanics (kinematics) of ATR injuries in professional male football players. Methods Eighty-six (n=86) consecutive ATR injuries in professional football players during official matches were identified. Sixty (70%) injury videos were identified for mechanism and situational pattern, with biomechanical analysis feasible in 42 cases. Three independent reviewers evaluated the injury videos. Distribution of ATR during the season, the match play and on the field were also reported. Results Fifty (n=50, 83%) injuries were classified as non-contact and 10 (17%) as indirect contact. ATRs are injuries occurring during accelerations; three main situational patterns were identified: (1) forward acceleration from standing (n=25, 42%); (2) cross-over cutting (n=15, 25%) and (3) vertical jumping (n=11, 18%). Biomechanically, ATR injuries were consistent with a multiplanar loading at the injury frame consisting of a slightly flexed trunk (15.5°), extended hip (−19.5°), early flexed knee (22.5°) and end-range dorsiflexed (40°) ankle in the sagittal plane and foot pronation; 27 (45%) ATRs occurred in the first 30 min of effective match time. Conclusions All ATRs in professional football were either non-contact (83%) or indirect contact (17%) injuries. The most common situational patterns were forward acceleration from standing, cross-over cutting and vertical jumping. Biomechanics was consistent and probably triggered by a multiplanar, although predominantly sagittal, loading of the injured Achilles tendon.
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Are foot posture and morphological deformation associated with ankle plantar flexion isokinetic strength and vertical drop jump kinetics? A principal component analysis
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Static measurements are clinically useful in characterising foot morphology, but it remains unclear to what extent it can influence dynamic lower limb performance. Therefore, the purpose of this study was to investigate if foot posture or foot morphology deformation relates to ankle plantarflexion isokinetic strength and specific kinetics variables during jumping using principal component analysis (PCA). Thirty-eight physically active participants performed drop vertical jump (DVJ) onto force platforms and ankle plantarflexion contractions in different modalities on an isokinetic dynamometer. Foot posture was assessed using the Foot Posture Index-6 item, whereas foot one-, two- and three-dimensional morphological deformation was calculated using the Arch Height Index Measurement System. A PCA was applied to the ankle plantarflexion and kinetics performance data and correlations between PCs and foot parameters measured. The analysis revealed 3 PCs within the ankle plantarflexion and DVJ kinetics variables that captured more than 80% of the variability within the data, but none of them showed significant correlations (r ≤ 0.27) with any foot variables. While foot posture and foot morphological deformation remain of interest in characterising foot morphology across individuals, these findings highlight the lack of clinical relevance of these static evaluations at characterising lower limb and ankle performance.
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The Lower Limbs of Sprinters Have Larger Relative Mass But Not Larger Normalized Moment of Inertia than Controls
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  • Oct 2022
Purpose: Sprinters exhibit inhomogeneous muscularity corresponding to musculoskeletal demand for sprinting execution. An inhomogeneous morphology would affect the mass distribution, which in turn may affect the mechanical difficulty in moving from an inertia perspective; however, the morphological characteristics of sprinters from the inertia perspective have not been examined. Here we show no corresponding differences in the normalized mass and normalized moment of inertia between the sprinters and untrained non-sprinters. Methods: We analyzed fat- and water-separated magnetic resonance images from the lower limbs of 11 male sprinters (100 m best time of 10.44-10.83 s) and 12 untrained non-sprinters. We calculated the inertial properties by identifying the tissue of each voxel and combining the literature values for each tissue density. Results: The lower-limb relative mass was significantly larger in sprinters (18.7 ± 0.7% body mass) than in non-sprinters (17.6 ± 0.6% body mass), while the normalized moment of inertia of the lower limb around the hip in the anatomical position was not significantly different (0.044 ± 0.002 vs. 0.042 ± 0.002 [a. u.]). The thigh relative mass in sprinters (12.9 ± 0.4% body mass) was significantly larger than that in non-sprinters (11.9 ± 0.4% body mass), whereas the shank and foot relative masses were not significantly different. Conclusions: We revealed that the mechanical difficulty in swinging the lower limb is not relatively larger in sprinters in terms of inertia, even though the lower-limb mass is larger, reflecting their muscularity. We provide practical implications that sprinters can train without paying close attention to the increase in lower-limb mass and moment of inertia.
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In human gait analysis studies, the entire foot is typically modeled as a single rigid-body segment; however, this neglects power generated/absorbed within the foot. Here we show how treating the entire foot as a rigid body can lead to misunderstandings related to (biological and prosthetic) foot function, and distort our understanding of ankle and muscle-tendon dynamics. We overview various (unconventional) inverse dynamics methods for estimating foot power, partitioning ankle vs. foot contributions, and computing combined anklefoot power. We present two case study examples. The first exemplifies how modeling the foot as a single rigid-body segment causes us to overestimate (and overvalue) muscle-tendon power generated about the biological ankle (in this study by up to 77%), and to misestimate (and misinform on) foot contributions; corroborating findings from previous multi-segment foot modeling studies. The second case study involved an individual with transtibial amputation walking on 8 different prosthetic feet. The results exemplify how assuming a rigid foot can skew comparisons between biological and prosthetic limbs, and lead to incorrect conclusions when comparing different prostheses/interventions. Based on analytical derivations, empirical findings and prior literature we recommend against computing conventional ankle power (between shank-foot). Instead, we recommend using an alternative estimate of power generated about the ankle joint complex (between shank-calcaneus) in conjunction with an estimate of foot power (between calcaneus-ground); or using a combined anklefoot power calculation. We conclude that treating the entire foot as a rigid-body segment is often inappropriate and ill-advised. Including foot power in biomechanical gait analysis is necessary to enhance scientific conclusions, clinical evaluations and technology development.
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Human ankle plantar flexor muscle–tendon mechanics and energetics during maximum acceleration sprinting
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  • Aug 2016
Tendon elastic strain energy is the dominant contributor to muscle-tendon work during steady-state running. Does this behaviour also occur for sprint accelerations? We used experimental data and computational modelling to quantify muscle fascicle work and tendon elastic strain energy for the human ankle plantar flexors (specifically soleus and medial gastrocnemius) for multiple foot contacts of a maximal sprint as well as for running at a steady-state speed. Positive work done by the soleus and medial gastrocnemius muscle fascicles decreased incrementally throughout the maximal sprint and both muscles performed more work for the first foot contact of the maximal sprint (FC1) compared with steady-state running at 5 m s-1 (SS5). However, the differences in tendon strain energy for both muscles were negligible throughout the maximal sprint and when comparing FC1 to SS5. Consequently, the contribution of muscle fascicle work to stored tendon elastic strain energy was greater for FC1 compared with subsequent foot contacts of the maximal sprint and compared with SS5. We conclude that tendon elastic strain energy in the ankle plantar flexors is just as vital at the start of a maximal sprint as it is at the end, and as it is for running at a constant speed.
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Lower-limb joint mechanics during maximum acceleration sprinting
Article
  • Oct 2019
We explored how humans adjust the stance phase mechanical function of their major lower-limb joints (hip, knee, ankle) during maximum acceleration sprinting. Experimental data (motion capture and ground reaction force (GRF)) were recorded from eight participants as they performed overground sprinting trials. Six alternative starting locations were used to obtain a dataset that incorporated the majority of the acceleration phase. Experimental data were combined with an inverse-dynamics-based analysis to calculate lower-limb joint mechanical variables. As forward acceleration magnitude decreased, the vertical GRF impulse remained nearly unchanged whereas the net horizontal GRF impulse became smaller due to less propulsion and more braking. Mechanical function was adjusted at all three joints, although more dramatic changes were observed at the hip and ankle. The impulse from the ankle plantar-flexor moment was almost always larger than those from the hip and knee extensor moments. Forward acceleration magnitude was linearly related to the impulses from the hip extensor moment (R 2 =0.45) and the ankle plantar-flexor moment (R 2 =0.47). Forward acceleration magnitude was also linearly related to the net work done at all three joints, with the ankle displaying the strongest relationship (R 2 =0.64). The ankle produced the largest amount of positive work (1.55±0.17 J/kg) of all the joints, and provided a significantly greater proportion of the summed amount of lower-limb positive work as running speed increased and forward acceleration magnitude decreased. We conclude that the hip and especially the ankle represent key sources of positive work during the stance phase of maximum acceleration sprinting.
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External mechanical work done during the acceleration stage of maximal sprint running and its association with running performance
Article
  • Feb 2019
This study aimed to elucidate how external mechanical work done during maximal acceleration sprint running changes with increasing running velocity and is associated with running performance. In twelve young males, work done at each step over 50 m from the start was calculated from mechanical energy changes in horizontal anterior-posterior and vertical directions and was divided into braking (-Wkap and -Wv, respectively) and propulsive (+Wkap and +Wv, respectively) phases. The maximal running velocity (Vmax) appeared at 35.87±7.76 m and the time required to run 50 m (T50 m) was 7.11±0.54 s. At 80% Vmax or higher, +Wkap largely decreased and -Wkap abruptly increased. The change in the difference between +Wkap and |-Wkap| (ΔWkap) at every step was relatively small at 70% Vmax or lower. Total work done over 50 m was 82.4±7.5 J kg-1 for +Wkap, 36.2±4.4 J kg-1 for |-Wkap|, 14.3±1.9 J kg-1 for +Wv, and 10.4±1.2 J kg-1 for |-Wv|. The total ΔWkap over 50 m was more strongly correlated with T50 m (r=-0.946, P<0.0001) than the corresponding associations for the other work variables. These results indicate that in maximal sprint running over 50 m, work done during the propulsive phase in the horizontal anterior-posterior direction accounts for the majority of the total external work done during the acceleration stage, and maximizing it while suppressing work done during the braking phase is essential to achieve a high running performance.
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Is Running Better than Walking for Reducing Hip Joint Loads?
Article
Purpose: Knowledge of hip biomechanics during locomotion is necessary for designing optimal rehabilitation programs for hip-related conditions. The purpose of this study was to: (1) determine how lower-limb muscle contributions to hip joint contact forces (HCFs) differed between walking and running; and (2) compare both absolute and per-unit-distance (PUD) loads at the hip during walking and running. Methods: Kinematic and ground reaction force data were captured from eight healthy participants during overground walking and running at various steady-state speeds (walking: 1.50±0.11 m/s and 1.98±0.03 m/s; running: 2.15±0.18 m/s and 3.47±0.11 m/s). A three-dimensional musculoskeletal model was used to calculate HCFs as well as lower-limb muscular contributions to HCFs in each direction (posterior-anterior; inferior-superior; lateral-medial). The impulse of the resultant HCF was calculated as well as the PUD impulse (BW.s/m) and PUD force (BW/m). Results: For both walking and running, HCF magnitude was greater during stance than swing, and was largest in the inferior-superior direction and smallest in the posterior-anterior direction. Gluteus medius, iliopsoas and gluteus maximus generated the largest contributions to the HCF during stance, whereas iliopsoas and hamstrings generated the largest contributions during swing. When comparing all locomotion conditions, the impulse of the resultant HCF was smallest for running at 2.15 m/s with an average magnitude of 2.14±0.31 BW.s, whereas the PUD impulse and force were smallest for running at 3.47 m/s with average magnitudes of 0.95±0.18 BW.s/m and 1.25±0.24 BW/m, respectively. Conclusions: Hip PUD loads were lower for running at 3.47 m/s compared to all other locomotion conditions because of a greater distance travelled per stride (PUD impulse) or a shorter stride duration combined with a greater distance travelled per stride (PUD force).
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Association of Sprint Performance With Ground Reaction Forces During Acceleration and Maximal Speed Phases in a Single Sprint
Article
  • Sep 2017
We aimed to clarify the mechanical determinants of sprinting performance during acceleration and maximal speed phases of a single sprint, using ground reaction forces (GRFs). While 18 male athletes performed a 60-m sprint, GRF was measured at every step over a 50-m distance from the start. Variables during the entire acceleration phase were approximated with a fourth-order polynomial. Subsequently, accelerations at 55%, 65%, 75%, 85%, and 95% of maximal speed, and running speed during the maximal speed phase were determined as sprinting performance variables. Ground reaction impulses and mean GRFs during the acceleration and maximal speed phases were selected as independent variables. Stepwise multiple regression analysis selected propulsive and braking impulses as contributors to acceleration at 55%-95% (β > 0.724) and 75%-95% (β > 0.176), respectively, of maximal speed. Moreover, mean vertical force was a contributor to maximal running speed (β = 0.481). The current results demonstrate that exerting a large propulsive force during the entire acceleration phase, suppressing braking force when approaching maximal speed, and producing a large vertical force during the maximal speed phase are essential for achieving greater acceleration and maintaining higher maximal speed, respectively.
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Why are Antagonist Muscles Co-activated in My Simulation? A Musculoskeletal Model for Analysing Human Locomotor Tasks
Article
  • Sep 2017
Existing “off-the-shelf” musculoskeletal models are problematic when simulating movements that involve substantial hip and knee flexion, such as the upstroke of pedalling, because they tend to generate excessive passive fibre force. The goal of this study was to develop a refined musculoskeletal model capable of simulating pedalling and fast running, in addition to walking, which predicts the activation patterns of muscles better than existing models. Specifically, we tested whether the anomalous co-activation of antagonist muscles, commonly observed in simulations, could be resolved if the passive forces generated by the underlying model were diminished. We refined the OpenSim™ model published by Rajagopal et al. (IEEE Trans Biomed Eng 63:1–1, 2016) by increasing the model’s range of knee flexion, updating the paths of the knee muscles, and modifying the force-generating properties of eleven muscles. Simulations of pedalling, running and walking based on this model reproduced measured EMG activity better than simulations based on the existing model—even when both models tracked the same subject-specific kinematics. Improvements in the predicted activations were associated with decreases in the net passive moments; for example, the net passive knee moment during the upstroke of pedalling decreased from 36.9 N m (existing model) to 6.3 N m (refined model), resulting in a dramatic decrease in the co-activation of knee flexors. The refined model is available from SimTK.org and is suitable for analysing movements with up to 120° of hip flexion and 140° of knee flexion.
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