ECSS Paris 2023: OP-BM09
INTRODUCTION: Vertical jumps are among most represented sport performance tests. Ground reaction force derived metrics (e.g., force, power, and force impulse) are commonly analysed. Prior research has investigated how characteristics of force-time profiles (e.g., timing of peak force [1], number of force peaks [2]) influence performance. Although a connection between the characteristics of the force-time curve and jump effectiveness is indicated, the challenge of identifying the optimal force-time profile necessitates further investigation. The aim of this paper is to address this knowledge gap by applying clustering approach based on ground reaction force variables of squat jump (SJ) and counter-movement jump (CMJ) force-time signals. METHODS: High-level athletes (basketball, soccer, tennis, long-distance running, dance, and martial arts; n=310)) participated. Three repetitions of SJ and CMJ were performed on Kistler force plate. K-means clustering method, that aims to partition n observations into k clusters in which each observation belongs to the cluster with the nearest mean, was applied to SJ and CMJ parameters. K-means clustering method was used to create 10 clusters, of which the 3 clusters with the highest representation were taken for further processing. Relative distances between cluster centres were calculated for each squat and countermovement jump parameter. RESULTS: 809 SJs were taken into analysis. Three clusters with highest representation of jumps were: cluster 1 with 375 jumps, cluster 2 with 241 jumps and cluster 3 with 177 jumps. The four SJ parameters with the highest relative distance between cluster centres among the three clusters were: force impulse between maximal force and take off, start interval relative power, force impulse in the 2nd half of push off and start interval velocity. 841 CMJs were taken into analysis. Three clusters with highest representation of jumps were: cluster 1 with 290 jumps, cluster 2 with 277 jumps and cluster 3 with 249 jumps. The four CMJ parameters with the highest relative distance between cluster centres among the three clusters were: force impulse in the 2nd half of push off, push off force impulse, force impulse in the 1st half of push off, positive force impulse. CONCLUSION: Results of this study demonstrate the grouping of vertical jump actions into force-time curve types that are distinct from one as reflected in more or less standard outcome metrics. This study is an entry step into quality of the SJ and CMJ ground reaction force curves with the ambition to upgrade applied value of this common athletic performance tests. 1. McHugh MP, Hickok M, Cohen JA, Virgile A, Connolly DAJ. Is there a biomechanically efficient vertical ground reaction force profile for countermovement jumps? Transl Sport Med. 2021;4(1):138–46. 2. Peng H Te, Song CY, Chen ZR, Wang IL, Gu CY, Wang LI. Differences between Bimodal and Unimodal Force-time Curves during Countermovement Jump. Int J Sports Med. 2019;40(10):663–9.
Read CV Nejc ŠarabonECSS Paris 2023: OP-BM09
INTRODUCTION: The eccentric utilization ratio (EUR), defined as the difference between countermovement jump (CMJ) and squat jump (SJ) performance, has been traditionally linked to elastic energy use and stretch-shortening cycle efficiency [1]. However, recent theories suggest higher EUR may also reflect different factors, such as poor concentric rate of force development (RFD) [2], questioning its role as an indicator of athletic performance. The aim of this series of exploratory studies is to contribute to the understating of the mechanisms underlying the variation in the magnitude of the EUR. METHODS: The paper presents a series of exploratory analyses based on data available from previous confirmatory studies and data from authors’ database. In all cases, vertical jumps (CMJ and SJ) were performed on a Kistler force plate (model 9260AA6). Three repetitions of each jump with 1-min rests were performed with hands placed on the hips, and the repetition with best jump height was take for further analysis. Jump heights was calculated using take-off velocity method. RESULTS: In the largest exploratory study, we compared EUR across 9 different sports (total n = 712), showing little difference between sports characterized by jumping (e.g., volleyball, basketball) and others. In the second analysis (n = 314; runners, basketball and soccer players) inverse correlations emerged between EUR and RFD in SJ (r = –0.41; p < .001), when the former was calculated based on force parameters. A third analysis (n = 45, volleyball) revealed that CMJ metrics exhibit larger correlation to performance proxies (sprint, agility and approach jump tests) than EUR. CONCLUSION: The results of the presented exploratory analyses align with the current theory on mechanisms driving variations in EUR [2]. Greater height in CMJ is largely underpinned by the build-up of force and muscle activation during the countermovement. Our analysis suggests that the remaining variation in EUR among individuals may be explained by different factors, and that EUR is not necessarily linked to superior athletic performance. Notably, poor concentric RFD and lower muscle stiffness were suggested to be related to lower SJ performance, and consequently, higher EUR. However, it has to be stressed that further studies are needed to reach firmer conclusions, as our analysis were purely exploratory. 1. McGuigan MR, Doyle TLA, Newton M, Edwards DJ, Nimphius S, Newton RU. Eccentric utilization ratio: Effect of sport and phase of training. J Strength Cond Res. 2006;20(4):992–5. 2. Van Hooren B, Zolotarjova J. The Difference between Countermovement and Squat Jump Performances: A Review of Underlying Mechanisms with Practical Applications. J Strength Cond Res. 2017;31(7):2011–20.
Read CV Žiga KozincECSS Paris 2023: OP-BM09
INTRODUCTION: Physical inactivity has harmful effects on health and is therefore a major public concern. Recently, we were able to show that high-intensity jump training was able to counteract the detrimental effects of 60 days bedrest on muscle and strength losses as well as on declines in aerobic capacity (Kramer et al. 2017). Within the ProPELL (Promoting Physical Exercise in Lab & Life) research project, we now investigated the effects of eight weeks of high-intensity jump training in non-exercising healthy young adults (Bieleke et al., 2022). We hypothesized to find increases in neuromuscular and aerobic capacity in the training group compared to a non-exercising control group. METHODS: Sixty-four young adults (34 female; mean age: 24.5 years, SD 3.5) were randomly assigned to either an eight-week high-intensity jump training or a control group. The training consisted of three weekly sessions of 15-minute high-intensity jump exercises aimed at improving neuromuscular and cardiovascular function. Pre and Post measurements included jump height and peak power during countermovement jumps, maximum isometric strength (leg extension in an isokinetic device), as well as maximum oxygen uptake (VO2peak) using a cycling spiroergometry protocol. We calculated ANOVAs (group * time) to analyze the data. RESULTS: Training improved jump height from 36±16 cm to 38±17 cm compared to control (37±16 cm to 37±15 cm; p<.001, d = 0.29). VO2peak increased in both groups without an interaction effect (training group: 33.3±17.4 to 35.4±16.6 ml/min*kg, control: 30.7±15.6 to 31.8 ± 17.6 ml/min*kg; p<.001, d = 0.9). No differences were found for the peak power of countermovement jumps and isometric maximal voluntary contraction during leg extension. CONCLUSION: A 15-minute jump training program three times a week increased jump-specific performance in a group of young healthy non-exercising adults. However, we did not find improvements in neuromuscular and cardiorespiratory fitness in this group. Since we have already shown such effects for jump training as a countermeasure to the detrimental effects of physical inactivity on neuromuscular and cardiorespiratory fitness (Kramer et al., 2017), we conclude that the "load" (intensity and volume) of jump training was not high enough in the present study to increase neuromuscular and cardiorespiratory fitness in healthy young adults. References: Bieleke, M., Fischer, U., Gruber, M., Kanning, M., Keim, D., Mier, D. Pruessner, J., Schüler, J. (2022). Promoting Physical Exercise in Lab and Life. Identifier DRKS00029727. https://drks.de/search/en/trial/DRKS00029727 Kramer, A., Gollhofer, A., Armbrecht, G., Felsenberg, D., & Gruber, M. (2017). How to prevent the detrimental effects of two months of bed-rest on muscle, bone and cardiovascular system: an RCT. Scientific reports, 7(1), 13177.
Read CV Philipp BarzykECSS Paris 2023: OP-BM09