Biomechanical Performance Factors in the Track and Field Sprint Start: A Systematic Review

thletics sprint events, the block start performance can be fundamental to the outcome of a race. This Systematic Review aims to identify biomechanical factors of critical importance to the block start and subsequent first two steps performance. A systematic search of relevant English-language articles was performed on three scientific databases (PubMed, SPORTDiscus, and Web of Science) to identify peer-reviewed articles published until June 2021. The keywords “Block Start”, “Track and Field”, “Sprint Running”, and “Kinetics and Kinematics” were paired with all possible combinations. Studies reporting biomechanical analysis of the block start and/or first two steps, with track and field sprinters and reporting PB100m were

was performed on three scientific databases (PubMed, SPORTDiscus, and Web of Science) to identify peer-reviewed articles published until June 2021. The keywords “Block Start”, “Track and Field”, “Sprint Running”, and “Kinetics and Kinematics” were paired with all possible combinations. Studies reporting biomechanical analysis of the block start and/or first two steps, with track and field sprinters and reporting PB100m were sought for inclusion and analysis. Thirty-six full-text articles were reviewed. Several biomechanical determinants of sprinters have been identified. In the “Set” position, an anthropometry-driven block setting facilitating the hip extension and a rear leg contribution should be encouraged. At the push-off, a rapid extension of both hips and greater force production seems to be important. After block exiting, shorter flight times and greater propulsive forces are the main features of best sprinters. This systematic review emphasizes important findings and recommendations that may be relevant for researchers and coaches. Future research should focus on upper limbs behavior and on the analysis of the training drills used to improve starting performance. Keywords: track and eld; sprinters; sprint start; block start; block velocity; biomechanics; kinematics; kinetics; sprint running; initial acceleration; sprint rst stance; sprint rst two steps 1. Introduction The 100 m race is perhaps the highlight of the Olympic Games, as it de nes who is the fastest man and woman in the world. In this type of event, the block start performance and the subsequent rst two steps can be of critical importance since they have a direct in uence on the overall 100 m time [1–8]. Given the importance of the sprint start, a new body of research has emerged in the past two decades that involved advanced technologies, high- precision methods, and sprinters of a higher performance level. For this reason, several technical (kinematic) and dynamic (kinetic) aspects are currently identi ed as determinant factors for starting block phase and initial sprint acceleration performances [1,4,6,9–25]. However, the concepts, outcomes, and ndings between studies are sometimes inconsistent and dif cult to interpret and conclude from. These inconsistencies may be accounted for Int. J. Environ. Res. Public Health2022,19, 4074.

this reason, several technical (kinematic) and dynamic (kinetic) aspects are currently identi ed as determinant factors for starting block phase and initial sprint acceleration performances [1,4,6,9–25]. However, the concepts, outcomes, and ndings between studies are sometimes inconsistent and dif cult to interpret and conclude from. These inconsistencies may be accounted for Int. J. Environ. Res. Public Health2022,19, 4074.

Int. J. Environ. Res. Public Health2022,19, 4074 2 of 74 by different study designs, methods, technologies of measure (e.g., external reaction forces under or on the blocks), statistical analyses, or more importantly, the ambiguity between samples of sprinters with different performance levels (e.g., elite, sub-elite, well-trained or trained) and/or between-group analyses based on the overall 100 m performance (i.e., personal best at 100 m—PB100m), and not on block performance. Although two important narrative reviews have already been published [26,27], to our knowledge, no previous review conducted a systematic search of literature exploring the inter-individual variability on block start performance across different performance levels. Thus, the main purposes of this systematic review were: (a) determine the biomechanical parameters of greatest in uence on the sprint start, including the “set” position and push-off phase, and the rst two steps of initial sprint acceleration and (b) identify the kinematic and kinetic biomechanical variables that best differentiate sprinters of different performance levels in each of those three phases of the sprint start. Considering the impact of the sprint in the sports eld and the absence of systematic studies on the kinematics and kinetics factors that determine success in block starts and initial sprint acceleration, we hypothesized that this systematic review will have a relevant impact on researchers to better design experimental/intervention studies, as well as constituting relevant support for coaches and athletes in the de nition of ef cient strategies for performance in the 100 m race. 2. Materials and Methods 2.1. Article Search, Eligibility, Inclusion, and Exclusion Criteria The systematic search of relevant articles was conducted based on PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines [28]. PubMed, Web of Science, and SPORTDiscus databases were searched for the following mesh terms: “Block Start” OR “Track and Field” OR “Sprint Running” OR “Acceleration” AND “Kinetics and Kinematics” pairing them with all possible combinations. In addition, lters for `English' and `articles' have been applied. The last search took place on 30 June 2021. The inclusion criteria were: publications in English; original observational and ex- perimental studies published in peer-reviewed journals; studies mainly focused

“Block Start” OR “Track and Field” OR “Sprint Running” OR “Acceleration” AND “Kinetics and Kinematics” pairing them with all possible combinations. In addition, lters for `English' and `articles' have been applied. The last search took place on 30 June 2021. The inclusion criteria were: publications in English; original observational and ex- perimental studies published in peer-reviewed journals; studies mainly focused on the block phase and/or one or two of the subsequent stance phases concerning kinematic and kinetic variables; and studies that included track and eld sprinters with the indication of their PB100m. The following types of records were excluded: conference abstracts; studies focused exclusively on the acceleration phase (beyond the rst two stance phases) or mainly focused on limitations imposed by motor and neurological impairments; studies reporting data referring to samples evaluated in previously published papers; studies not mentioning the performance level of the sprinters through their PB100m; case reports; and studies without reference to biomechanical variables. The records identi ed from the databases with the aforementioned mesh terms were exported to the reference manager software EndNote X8 that eliminated duplicates. All articles' eligibility was then assessed independently by two reviewers' authors (JMA and FC). The articles identi ed were rst screened by title and abstract for relevance. Studies that raised any uncertainty in exclusion were conservatively retained for subsequent full- text review. The full text of the articles selected as relevant or having raised uncertainty in exclusion was read and further scrutinized for meeting the inclusion criteria and their quality was evaluated. Disagreements on nal inclusion or exclusion of studies were resolved by consensus, and if disagreement persisted, a third reviewer ( rst author, MJV) was available for adjudication. Articles that did not meet the selection criteria or presented a quality score below 50% were excluded. 2.2. Quality of the Studies The study quality of each publication was evaluated according to the guidelines of the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Initiative [29]. This analysis was based on 22 items. Title and abstract. Introduction: back- ground and rationale. Methods: study design, setting, participants, variables, data sources,

a quality score below 50% were excluded. 2.2. Quality of the Studies The study quality of each publication was evaluated according to the guidelines of the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Initiative [29]. This analysis was based on 22 items. Title and abstract. Introduction: back- ground and rationale. Methods: study design, setting, participants, variables, data sources,

Int. J. Environ. Res. Public Health2022,19, 4074 3 of 74 bias, sample size, quantitative variables, and statistical methods. Results: participants, descriptive data, outcome data, main results, and other analyses. Discussion: key results, limitations, interpretation, and generalizability. Funding. These criteria were scored on a binary scale (1 = yes, 0 = no) independently by two of the authors, and a quality score was then calculated for each study by adding its binary scores and dividing the result by the maximum possible score the study could have achieved. This was then expressed as a percentage to re ect a measure of methodological quality. The quality scores were classi ed as follows (a) low methodological quality for scores < 50%; (b) good methodological quality for scores between 50% and 75%; and (c) excellent methodological quality for scores > 75%. The studies with a score lower than 50% [30] were excluded from the systematic review. The inter-rater reliability analysis was evaluated by the Cohen's Kappa for nominal variables (2 dimensions) [31]. Standards for strength of agreement for the kappa coef cient were: 0 = poor,0.01–0.20 = slight, 0.21–0.40 = fair, 0.41–0.60 = moderate, 0.61–0.80 = substantial, and 0.81–1 = almost perfect [32]. 2.3. Data Extraction An Excel form was used for data extraction. Of each manuscript selected for review, the following information was extracted from each included study: (a) the primary focus of study, means the phase of sprint start, e.g., block phase, rst stance, and study design; (b) the main purpose, e.g., associations between biomechanical variables of starting blocks and the sprint start performance, comparing athletes of different performance levels, comparing different footplate spacing and block angles; (c) type of kinematic and kinetic analyses systems used—two dimensional (2D) or three dimensional (3D) analysis and starting blocks instrumented or placed on force platforms; (d) study sample—the number per gender of participants, and per level of expertise of participants according with the authors, and their PB100m; (e) biomechanical measurement protocols—the variables used to characterize the biomechanical factors of sprint start, number and distance of repeated trials; and (f) key ndings of sprint start kinematic and

and starting blocks instrumented or placed on force platforms; (d) study sample—the number per gender of participants, and per level of expertise of participants according with the authors, and their PB100m; (e) biomechanical measurement protocols—the variables used to characterize the biomechanical factors of sprint start, number and distance of repeated trials; and (f) key ndings of sprint start kinematic and kinetic factors. 3. Results 3.1. Search Results The initial search identified 756 titles in the described databases. With the reference man- ager software, 406 duplicates were eliminated automatically. The remaining 350 articles were then screened according to title and abstract for relevance, resulting in another289 studies being eliminated from the database. The full text of the remaining 61 articles was read and another 22 were rejected for not meeting the inclusion criteria defined for the current study and 3 studies were excluded for not meeting the quality criteria (quality index < 50%). A total of 36 studies was fully reviewed. Studies were excluded in the screening stage due to not including track and field athletes or sprint starts using starting blocks (n = 289). In the eligibility stage, there were several reasons for exclusion, namely studies with results focused exclusively on the acceleration phase (n = 8), case studies (n = 4), studies reporting data referring to samples of previously published papers (n = 3) or mainly focused on the limitations of disability (n = 3), lack of in- formation about the PB100m (n = 2) and studies presenting only results for electromyography and reaction time data (n = 2). Figure

Int. J. Environ. Res. Public Health2022,19, 4074 4 of 74Int. J. Environ. Res. Public Health 2022, 19, x FOR PEER REVIEW 4 of 69 Figure 1. Flow diagram of the study selection process according to PRISMA guidelines. 3.2. Quality of Studies In the evaluation of methodological quality, the inter-rater reliability analysis achieved a Kappa value of 0.91 (0.84–0.98), indicating almost perfect agreement between raters. The mean quality score of the included studies was 74.92%. None of the studies achieved the maximum score of 100% and 3 studies (excluded) scored below 50%. Sixteen studies were classified with good methodological quality (quality score between 50 and 75%), while 20 studies had excellent methodological quality (quality score > 75%). The main deficiencies in methodological quality were related to the estimation of sample size and study limitations discussion. 3.3. Basic Characteristics of Included Studies Fifteen studies [2,3,10–12,17,20,21,23,25,33–37] focused specifically on the block phase, 18 studies [1,4–8,13–16,18,19,24,38–42] on the block phase and, at least one of the subsequent two flight and stance phases, and 3 studies [9,22,43] on the initial acceleration (the first and/or the second step). A summary of all the individual studies reviewed is presented in Table 1. Figure 1.Flow diagram of the study selection process according to PRISMA guidelines. 3.2. Quality of Studies In the evaluation of methodological quality, the inter-rater reliability analysis achieved a Kappa value of 0.91 (0.84–0.98), indicating almost perfect agreement between raters. The mean quality score of the included studies was 74.92%. None of the studies achieved the maximum score of 100% and 3 studies (excluded) scored below 50%. Sixteen studies were classi ed with good methodological quality (quality score between 50 and 75%), while20 studieshad excellent methodological quality (quality score > 75%). The main de ciencies in methodological quality were related to the estimation of sample size and study limitations discussion. 3.3. Basic Characteristics of Included Studies Fifteen studies [2,3,10–12,17,20,21,23,25,33–37] focused specifically on the block phase, 18 studies [1,4–8,13–16,18,19,24,38–42] on the block phase and, at least one of the subsequent two flight and stance phases, and 3 studies [9,22,43] on the initial acceleration (the first and/or the

methodological quality were related to the estimation of sample size and study limitations discussion. 3.3. Basic Characteristics of Included Studies Fifteen studies [2,3,10–12,17,20,21,23,25,33–37] focused specifically on the block phase, 18 studies [1,4–8,13–16,18,19,24,38–42] on the block phase and, at least one of the subsequent two flight and stance phases, and 3 studies [9,22,43] on the initial acceleration (the first and/or the second step). A summary of all the individual studies reviewed is presented in Table

Int. J. Environ. Res. Public Health2022,19, 4074 5 of 74 Table 1. Studies are listed in reverse-chronological order by year, followed by alphabetically for studies published in the same year. Samples (n) are restricted to total participating sprinters and are classi ed by performance level(s) according to the original authors. Study Details Sample Main Findings Quality Reference Primary Focus of the Study Main Purpose Biomechanics Analysis Sex n Level PB100m (s) Mean Score (%) Werkhausen, Willwacher [43] First 2 steps. Two force platforms for the GRFs of the rst 2 steps. Three- dimensional kinematic model (pelvis and lower limbs) Investigate how plantar exor muscle-tendon behavior is modulated during the rst 2 steps 3D GRF of the rst 2 steps F 11 Germany national level 12.66 0.49 Ankle and knee joint angles revealed no statistical differences at any time of both steps. Ankle joint power was negative after touchdown and positive during the rest of the stance phase, whereas net ankle joint work was positive during both steps. Knee joint power was positive during most of the stance phase. 67.78 Graham-Smith, Colyer [39] Block phase and rst 2 steps. An array of 6 force platforms. Compare force production between elite senior and junior academy sprinters 3D block and rst 2 steps GRF, and spatiotemporal data M M 17 20 Elite Senior Junior Academy 8.2% worse than senior WR (a) 12.2% worse than junior WR (b) Senior sprinters presented higher relative anteroposterior force and power during the initial block phase, higher forces during the transition from bilateral to unilateral pushing and lower (more horizontal) projection angle across the initial 2 steps of the sprint compared with junior athletes. 76.82 Nagahara, Gleadhill [35] Block phase. Two force platforms with a coordinate transformation matrix to the coordinate block system. Examine whether modulation of COP location on the starting block improves sprint start performance 3D GRF under each block and spatiotemporal data M 20 National level 11.22 0.41 The modulation of COP location did not show an effect on AHEP and 10 m time. However, instructing to push the calcaneus onto the block (posterior location)

to the coordinate block system. Examine whether modulation of COP location on the starting block improves sprint start performance 3D GRF under each block and spatiotemporal data M 20 National level 11.22 0.41 The modulation of COP location did not show an effect on AHEP and 10 m time. However, instructing to push the calcaneus onto the block (posterior location) may improve the 10 m time and/or AHEP for some individuals and may be accomplished through a shorter reaction time. 82.50 Sado, Yoshioka [23] Block phase. Separated starting blocks secured onto separate force plates. Examine the 3D lumbo-pelvic- hip kinetics during block start 3D GRF under each block M 12 University of Tokyo team 10.78 0.19 The peak lumbosacral extension torque was larger than any other peak torque. 66.36

The review identifies key biomechanical factors affecting sprint start performance.