Measurement errors when estimating the vertical jump height with flight time using photocell devices: the example of Optojump.

Common methods to estimate vertical jump height (VJH) are based on the measurements of flight time (FT) or vertical reaction force. This study aimed to assess the measurement errors when estimating the VJH with flight time using photocell devices in comparison with the gold standard jump height measured by a force plate (FP). The second purpose was to determine the intrinsic reliability of the Optojump photoelectric cells in estimating VJH. For this aim, 20 subjects (age: 22.50±1.24 years) performed maximal vertical jumps in three modalities in randomized order: the squat jump (SJ), counter-movement jump (CMJ), and CMJ with arm swing (CMJarm). Each trial was simultaneously recorded by the FP and Optojump devices. High intra-class correlation coefficients (ICCs) for validity (0.98-0.99) and low limits of agreement (less than 1.4 cm) were found; even a systematic difference in jump height was consistently observed between FT and double integration of force methods (-31% to -27%; p<0.001) and a large effect size (Cohen's d>1.2). Intra-session reliability of Optojump was excellent, with ICCs ranging from 0.98 to 0.99, low coefficients of variation (3.98%), and low standard errors of measurement (0.8 cm). It was concluded that there was a high correlation between the two methods to estimate the vertical jump height, but the FT method cannot replace the gold standard, due to the large systematic bias. According to our results, the equations of each of the three jump modalities were presented in order to obtain a better estimation of the jump height.

The effect of slope on repeated sprint ability in young soccer players.

This study aimed to describe a gradient repeated sprint ability (RSA) test in comparison with a standard level one by investigating performance, metabolic demand and muscular jumping performance as a proxy for running mechanics. Eighteen athletes performed two level RSA tests (40 m × 6) - for reliability evaluation - and one ±5% gradient RSA test, second leg downhill (RSAgrad). Rating of perceived exertion (RPE), blood lactate concentration (BLa) concentration, vertical jump heights were assessed as well. Level test measures resulted highly reliable (Intra-class correlation coefficient (ICC) ≥0.96). RSAgrad worsened only first sprints' performance (-2%) but not overall test performance (~45 s). RSAgrad resulted to be less deteriorating in terms of fatigue index (FI) (-36%), BLa (-23%), RPE (-11%), jumping performance (RSAgrad post-/pre-squat jump, countermovement jump heights (CMJh): -3%, -6%, respectively). RSAgrad could be used to diversify common training protocol without stressing excessively athletes' current metabolic-anaerobic capacity. Such physical conditioning procedures could improve acceleration/braking capability.

Effect of different recovery durations between bouts in 3-a-side games on youth soccer players' physiological responses and technical activities.

AIM: The aim of this study was to investigate the effects of the length of recovery durations between bouts in 4x4min 3-a-side small-sided games (SSG) on time-motion analysis, technical actions and physiological responses of players. METHODS: Twelve young soccer players participated in 4 different 3-a-side games in which the recovery durations between bouts were different (R1: 1 min, R2: 2 min, R3: 3 min, and R4: 4 min). Heart rate (HR), total distance covered in different speed zones, and technical performance were monitored during all SSGs, whereas the rating of perceived exertion (RPE, CR-10) and venous blood lactate were determined at the end of the last bout of each SSG. RESULTS: Results showed that SSGs-R1 induced higher %HRreserve and lower successful passes (vs. R3 and R4 conditions, P<0.05), lower total passes (vs. R4 conditions, P<0.05), and greater distance covered in walking zone (0-6.9 km.h⁻¹) (vs. other 3 conditions, P<0.05). In addition, during the SSG-R3 players covered greater distances in high-intensity running zone (>18 km.h-1), performed more tackles (vs. R1 condition, P<0.05) and had more ball contacts (vs. R1 and R2 conditions, P<0.05). CONCLUSION: According to these results, it is thought that R1 and R2 are suitable for inducing higher physiological responses, while R3 and R4 are more appropriate for training aim to improve technical skills in 4x4min 3-a-side SSGs among young soccer players. These findings provide evidence for coaches to justify the selection of recovery duration between bouts in 3-a-side SSGs among young soccer players.

Physical and technical comparisons between various-sided games within professional soccer.

This study compared the technical activity and physical movements of various-sided games within professional soccer. It also examined the test-retest reliability of sided games using various numbers of players. 10 elite male players from a Scottish Premier League performed small- (SSGs: 4 vs. 4), medium- (MSGs: 5 vs. 5 to 8 vs. 8) and large- (LSGs: 9 vs. 9 to 11 vs. 11) sided games each lasting for 3×5 min. Results show significant physical differences (p<0.05) between SSGs, MSGs and LSGs for most of the variables measured. It was shown that SSGs induce a significantly faster playing speed when compared to MSGs and LSGs (150.5 vs. 108.3 vs. 120.4 m.min-1, p<0.01) but significantly less (p<0.01) repeated high-intensity efforts (0.88 vs. 4.40 m), high-intensity running (7 vs. 39 m) and sprint distance (0 vs. 11 m) when compared to LSGs. Findings also revealed significant differences (p<0.05) between SSGs, MSGs and LSGs in technical demands (passes, dribbles, shots, headers). High levels of reproducibility (ICC=0.99) were yielded when using the same-sided games, pitch sizes and possession rules. This study provided information on different-sided games to facilitate its use as part of a periodised weekly structure.

Comparison of ground reaction forces and contact times between 2 lateral plyometric exercises in professional soccer players.

There are no studies which have examined the differences in kinetics between lateral plyometric exercises and the selection of these exercises is largely based on the experience and observation of coaches. This study aimed to compare ground reaction forces (GRF) and contact times (GCT) between 2 lateral plyometric exercises: lateral alternative leg hopping (HOP), and speed lateral footwork (SPEED). 16 professional male soccer players (age: 24.6±5.5 years; and BMI: 21.7±2.2 kg.m - 2) participated in this within-participant repeated measures study. 3-dimensional GRF data were measured by force platform. Our study revealed significant differences between the 2 lateral plyometric exercises in all kinetics parameters (F=573.7, P<0.01). HOP produced significantly longer GCT (0.45 s vs. 0.23 s, P<0.01, large effect), significantly higher values (P<0.05, large effect) in peak force (3.31 vs. 2.47 Body Weight [BW]), peak rate of force development (0.94 vs. 0.29 BW/s), and impulse (0.76 vs. 0.31 BW.s) except for peak force in the medial-lateral (P<0.05, medium effect) and impulse in the anterio-posterior direction (not significant, small effect). Therefore, SPEED is an exercise that aims to increase step frequency because of its short GCT (< 0.25 s) while HOP increases leg strength and power.

Effects of time-of-day on oxidative stress, cardiovascular parameters, biochemical markers, and hormonal response following level-1 Yo-Yo intermittent recovery test.

The aim of this study was to investigate the effect of time-of-day on oxidative stress, cardiovascular parameters, muscle damage parameters, and hormonal responses following the level-1 Yo-Yo intermittent recovery test (YYIRT). A total of 11 healthy subjects performed an intermittent test (YYIRT) at two times-of-day (i.e., 07:00 h and 17:00 h), with a recovery period of ≥36 h in-between, in a randomized order. Blood samples were taken at the rest (baseline) and immediately (post-YYIRT) after the YYIRT for measuring oxidative stress, biochemical markers, and hormonal response. Data were statistically analyzed using one-way and two-way repeated measures ANOVA and Bonferroni test at p < 0.05. Observed power (α = 0.05) and partial eta-squared were used. Our results showed that oxygen uptake (VO2max), maximal aerobic speed, and the total distance covered tended to be higher in the evening (17:00 h). There was also a main effect of time-of-day for cortisol and testosterone concentration, which were higher after the YYIRT in the morning (p < 0.05). The heart rate peak and the rating of perceived exertion scales were lower in the morning (p < 0.05). However, the plasma glucose (p < 0.01), malondialdehyde, creatine kinase (p < 0.01), lactate dehydrogenase (p < 0.05), high-density lipoprotein (p < 0.01), total cholesterol (p < 0.01), and triglycerides (p < 0.05) were higher after the YYIRT in the evening. Low-density lipoprotein, systolic blood pressure, diastolic blood pressure, and lactate levels (p > 0.05) were similar for the morning and evening test. In conclusion, our findings suggest that aerobic performance presents diurnal variation with great result observed in the evening accompanied by an improvement of hormonal, metabolic, and oxidative responses. These data may help to guide athletes and coaches and contribute to public health recommendations on exercise and muscle damage particularly in the competitive periods.

Effects of custom-made textile insoles on plantar pressure distribution and lower limb EMG activity during turning.

BACKGROUND: Turning during locomotion involves considerable changes of the body's center of mass and reduced stability, as well as lower limb kinematics and kinetics. However, many previous studies have been carried out to evaluate the effectiveness and applications of orthotic insoles as well as different types of orthotic materials in various clinical symptoms, which are focused primarily on straight line walking. Hence, the influence of custom-made insoles with the use of advanced three-dimensional spacer fabrics on biomechanics parameters in terms of plantar pressure distribution and lower limb electromyography during turning movement was studied. METHODS: Twelve subjects performed 180-degree turning at a speed 3.07-3.74 km/h for five successful trials under 3 insoles conditions: wearing traditional ethylene vinyl acetate insoles and two different spacer-fabricated insoles, with the plantar pressure and lower limb muscle activity collected simultaneously. Turning movement was broken down into 3 phases for analysis: Turning initiation, turn around and turn termination. RESULTS: There was a statistically significance difference in plantar pressure between the traditional insoles and the insoles made of a spacer fabric as the top layer (p < 0.05). Compared to the traditional insoles, insoles made of a spacer fabric reduced the peak pressure (>12 %) and pressure-time integral (>13 %) in toes, metatarsal head 1 and metatarsal heads 2-3 at turning initiation; (>15 %) and (>17 %) in medial midfoot and medial heel at turn around. Insoles with spacer fabrics on the top and middle layer reduced both pressure parameters (>18 %) in toes and MTH 1 at turn termination. In terms of muscle activities, insoles with two-layer spacer fabrics could lower maximum muscle activities of vastus lateralis (>16 %; p < 0.05) at turn around. CONCLUSIONS: Insoles with different fabrications could offer various pressure offloading patterns across the plantar and muscle activity changes while turning. Insoles with a spacer fabric on the top tend to reduce plantar pressure loading at different regions during turn initiation and turn around phases, while two-layer spacer-fabricated insoles may contribute to reduced vastus lateralis muscle activation during turn around. More importantly, this study provides a new dimension in the potential use of the textile-fabricated insoles which may widen the range of insole materials selection in the design and development of insoles so as to enhance the effectiveness of orthotic treatment.

Strength and body composition changes in recreationally strength-trained individuals: comparison of one versus three sets resistance-training programmes.

PURPOSE: The purpose of this study was to determine the effects of increasing the volume of weight-training from one to three sets upon body composition and muscular strength. METHODS: Sixteen male weight-trainers volunteered to act as subjects and were randomly assigned to one of two training groups. Supervised weight-training targeting the upper body was conducted three times per week for eight weeks using one set (n = 8) or three sets (n = 8) of six repetitions to fatigue. Subjects were measured before and after the training intervention for (1) strength performance (N and kg) and (2) adiposity (sum of seven skinfold thicknesses in mm). RESULTS: Both training groups improved significantly (20.7%) in terms of muscular strength (P < 0.05) with no differences being observed between the one set (21.98% increase) and three set group (20.71% increase) after the training interventions (P > 0.05). Significant decreases were also observed for skinfold measures in the one set group (P < 0.05). CONCLUSIONS: One set of high intensity resistance training was as effective as three sets for increasing the strength of muscle groups in the upper body. The one set protocol also produced significantly greater decreases in adiposity.

Technical and physical demands of small vs. large sided games in relation to playing position in elite soccer.

The aim of this investigation was to compare the effects of common rule changes on technical and physical demands for elite soccer players in five playing positions during various 4-min small-sided games (SSGs) in comparison to 11-a-side matches. Forty international players classified into five positional roles participated in the study (25.3±2.4 years, 182.4±2.3 cm, 77.3±4.1 kg; M±SD). Players completed three different conditioned small-sided 4 vs. 4 games (1 ball touch=1T, 2 ball touches=2T and Free Play=FP) as well as two friendly matches. Heart rate (HR), blood lactate ([La]), ratings of perceived exertion (RPE) as well as physical and technical performance were analyzed. Compared to match-play, total distance covered per minute of play, high-intensity running activities (sprinting and high-intensity runs), total numbers of duels and lost ball possessions were significantly greater within SSGs for all playing positions (p<.05). In contrast, [La], percentage of successful passes and number of ball possessions were lower (p<.05) within SSGs, particularly with 1T and 2T rules, in comparison with match-play. HR was higher in SSGs compared to match-play for all playing positions, and RPE values were lower (p<.05) during the FP SSG for defensive midfielders, wide midfielders and forwards. In conclusion, this study revealed that 4 vs. 4 SSGs played with 1 or 2 ball touches increased the high-intensity running and the difficulty to perform technical actions, being more specific to match demands. Subsequently, it is of importance for coaches to understand the different physiological demands imposed upon players by varying the rules of SSGs and to understand the differences between positional roles.