The purpose of the present study was (i) to explore the reliability of the most commonly used countermovement jump (CMJ) metrics, and (ii) to reduce a large pool of metrics with acceptable levels of reliability via principal component analysis to the significant factors capable of providing distinctive aspects of CMJ performance. Seventy-nine physically active participants (thirty-seven females and forty-two males) performed three maximal CMJs while standing on a force platform. Each participant visited the laboratory on two occasions, separated by 24–48 h. The most reliable variables were performance variables (CV = 4.2–11.1%), followed by kinetic variables (CV = 1.6–93.4%), and finally kinematic variables (CV = 1.9–37.4%). From the 45 CMJ computed metrics, only 24 demonstrated acceptable levels of reliability (CV ≤ 10%). These variables were included in the principal component analysis and loaded a total of four factors, explaining 91% of the CMJ variance: performance component (variables responsible for overall jump performance), eccentric component (variables related to the breaking phase), concentric component (variables related to the upward phase), and jump strategy component (variables influencing the jumping style). Overall, the findings revealed important implications for sports scientists and practitioners regarding the CMJ-derived metrics that should be considered to gain a comprehensive insight into the biomechanical parameters related to CMJ performance.

Physical abilities modelling has a profound connection with long-term athlete development and talent identification. There is not enough data to support evidence about age-related changes in volleyball players’ isometric strength. This study aimed to define the age-related model of volleyball players multidimensional muscles’ contractile characteristics. The participants were divided according to gender (male n = 112, female n = 371) and according to age into four groups: under 15 (U15), under 17 (U17), under 19 (U19), and under 21 (U21) years old. Participants performed three isometric strength tests: handgrip, lumbar extensors, and ankle extensors. Maximal force and rate of force development results from all three tests were transformed into a single Score value as a representation of contractile potentials using principal component analysis. The main findings were that Score values of both genders showed significant differences between age groups (male: F = 53.17, p < 0.001; Female: F = 41.61, p < 0.001). Trends of those yearly changes were slightly more balanced for female subjects (3.9%) compared to male subjects (6.3%). These findings could help in strength training adjustments when working with volleyball players of a certain age, and enable coaches to detect ones that stand out positively, considering them as strong in regard to their age.

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Introduction When a person is in a standing position, the plantar flexor muscles are involved in most static and dynamic body movements. Objectives The aim of this study was to investigate the trial to trial and factorial reliability of measuring the contractile characteristics of PF muscles using a simple novel field test. Methods The sample consisted of 452 healthy subjects, 120 male and 332 female. The research was conducted by means of the trial to trial testing method, using isometric dynamometry performed in field conditions. ANOVA was used to estimate the differences among the trials, Cronbach’s alpha and interclass correlation to estimate the correlations among the trials, and principal component analysis to evaluate the contribution of each trial to overall variability. Results The main findings of this study are that trials differed significantly (p<0.000) for maximal force (Fmax) and maximal rate of force development (RFDmax), indicating that the three procedural trials were necessary. The trials were highly correlated (Fmax, RFDmax, r>0.9), proving that measuring was reliable, and the factorial analysis separated the second and third trials, the second trial accounting for most of the total variability. Conclusions The simple novel field test for the measurement of plantar flexor contractile characteristics recommended by this study proved to be as highly reliable as laboratory testing, but was easy to perform in conditions outside of scientific or diagnostic institutions, which greatly facilitates the work of scientists, coaches and professionals. Level of Evidence II; Diagnostic Studies – Investigating a diagnostics test.

Rezime:Savremeni čovek sve više živi sedentarnim načinom života. Ljudi danas provode sate gledajući televiziju, radeći za računarom ili jednostavno provode vreme neaktivni. Ipak, pod uticajem sve prisutnijih socijalnih medija pokrenut je značajan broj sajtova koji se bave posebnim režimima ishrane, angažovanjem ličnih trenera, kupovine fitnes opreme, tako da je danas članstvo u nekom fitnes klubu postalo skoro uobičajena stvar za mnoge ljude. Ova potreba čoveka modernog doba dovela je do stvaranja globalne fitnes industrije, čija se vrednost danas meri bilionima dolara. Savremeni softveri omogućili su ljudima da lako prate efekte svog treninga putem mobilnih aplikacija i wearable tehnologije. Predviđanja su da će ove tehnologije imati sve veću primenu i rast u fitnes industriji. Ipak, potrebno je napomenuti da tehnologija ne može u potpunosti da zameni živog fitnes stručnjaka u davanju najboljih saveta i instrukcija za vežbanje. UVODOd pojave prve komercijalne vežbaonice (gym) u Briselu 1840. godine do današnjih dana, fitnes industrija je evoluirala u jedan od najbrže rastućih biznisa današnjice. Pravi proboj u fitnes industriji desio se tokom 80-ih godina prošlog veka otvaranjem lanaca vežbaonica kao što su 24 Hour Fitness (1983) i LA Fitness (1984). Takođe, pojava video tehnologije dovela je do planetarne popularnosti Džejn Fonda video časova vežbanja od kojih je nastao ceo pokret Aerobik.Megalanci vežbaonica postoje i danas, ali kao kod mnogo drugih stvari, današnji potrošači traže više individualni i lični pristup, tako da je tokom 1990-ih i 2000-ih godina došlo do otvaranja brojnih, manjih klubova zdravlja (health clubs), do povećane tražnje za ličnim trenerima i pojave drugih, specijalizovanih vežbaonica tipa Cross-Fit, Crunch Fitness, Fit Body Boot Camp i drugih franšiza. U poređenju sa ranijim generacijama, današnja populacija živi više sedentarnim načinom života. Ljudi danas provode sate gledajući televiziju, radeći za računarom ili jednostavno provode vreme neaktivni. Takođe,