A comparison of vertical and horizontal reactive strength index variants and association with change of direction performance

This study sought to investigate the inter-relationship between different vertical and horizontal variants of reactive strength index (RSI) and change of direction performance. Thirty-one male volleyball players (age: 22.4 ± 3.9 years), performed bilateral drop jumps (DJ), bilateral and unilateral countermovement jumps (CMJ), and triple hops for distance. The RSI was calculated as the ratio of jump height and contact time (DJ), jump height and time to take off (CMJ), and flight time or hop distance and contact time (triple hop), and 505 change of direction test. RSI obtained from DJ and CMJ tasks exhibited excellent trial-to-trial reliability (ICC = 0.91-0.94), while triple hop based RSI had only moderate reliability (ICC = 0.67-0.74). The relationships among different RSI variants were moderate to high (i.e. DJ to CMJ: r = 0.57-0.69; p ≤ 0.004; DJ to triple hop: r = 0.54-0.66; p ≤ 0.021 and CMJ to triple hop: r = 0.42-0.63; p ≤ 0.037). For the triple hop, the associations between RSI based on hop flight time and RSI based on hop distance were high for hop 1-2 (r = 0.77-0.83; p < 0.001) and very high for hop 2-3 (r = 0.91-0.92; p < 0.001). All RSI variants were in small to moderate negative correlation with 505 test performance (r = -0.38 to -0.45; p ≤ 0.042). The agreement in inter-limb asymmetry direction between in RSI from unilateral CMJ and triple hop RSI variables was slight to moderate (Kappa coefficient = 0.06-0.36). In conclusion, although inter-relationships between RSI variants were moderate to high, the direction of inter-limb asymmetry was inconsistent, highlighting the notion of movement variability in limb dominance

Levels of agreement for the direction of inter-limb asymmetry during four simple change-of-direction tests in young male handball players: a pilot study

The purpose of this pilot study was to investigate the effects of change-of-direction (CoD) angle (90° vs. 180°) and the inclusion of acceleration approach on total task time, CoD deficit, and agreement regarding inter-limb asymmetry direction across CoD tasks. The sample included 13 young male handball players (age: 22.4 ± 3.2 years). The CoD tasks were performed over a 10 m distance with 90° and 180° turns. Both CoD tasks were performed under two conditions: (1) from the standing start and, (2) with a 10 m prior acceleration approach. Linear sprint times over a 10 m distance were also recorded for the purpose of determining the CoD deficit. The differences between the outcomes of different test variants were assessed with pairwise t-tests and associated Cohen’s d effect size. The agreement in terms of inter-limb asymmetry direction was assessed descriptively, using percentage of agreement. Results showed that the inclusion of the 10 m approach reduced the total task time (mean differences ranging between 0.26 and 0.35 s; d = 2.27–4.02; p 0.002). The differences between 90° and 180° turn times were statistically significant under both conditions: (a) without approach (0.44–0.48 s; d = 4.72–4.84; all p 0.001), and (b) with approach (0.50–0.54 s; d = 4.41–5.03; p 0.001). The agreement regarding inter-limb asymmetry direction among the tasks was 30.7–61.5%. The differences between the tasks could be explained by the angle–velocity trade-off. The results of this study imply that the CoD tasks should not be used interchangeably when assessing inter-limb asymmetries

An assessment of the hopping strategy and inter-limb asymmetry during the triple hop test: a test–retest pilot study

The aims of the present study are to: (1) determine within- and between-session reliability of multiple metrics obtained during the triple hop test; and (2) determine any systematic bias in both the test and inter-limb asymmetry scores for these metrics. Thirteen male young American football athletes performed three trials of a triple hop test on each leg on two separate occasions. In addition to the total distance hopped, manual detection of touch down and toe-off were calculated via video analysis, enabling flight time (for each hop), ground contact time (GCT), reactive strength index (RSI), and leg stiffness (between hops) to be calculated. Results showed all coefficient of variation (CV) values were ≤ 10.67% and intraclass correlation coefficients (ICC) ranged from moderate to excellent (0.53–0.95) in both test sessions. Intrarater reliability showed excellent reliability for all metrics (CV ≤ 3.60%, ICC ≥ 0.97). No systematic bias was evident between test sessions for raw test scores (g = −0.34 to 0.32) or the magnitude of asymmetry (g = −0.19 to 0.43). However, ‘real’ changes in asymmetry (i.e., greater than the CV in session 1) were evident on an individual level for all metrics. For the direction of asymmetry, kappa coefficients revealed poor-to-fair levels of agreement between test sessions for all metrics (K = −0.10 to 0.39), with the exception of the first hop (K = 0.69). These data show that, given the inherent limitations of distance jumped in the triple hop test, practitioners can confidently gather a range of reliable data when computed manually, provided sufficient test familiarization is conducted. In addition, although the magnitude of asymmetry appears to show only small changes between test sessions, limb dominance does appear to fluctuate between test sessions, highlighting the value of also monitoring the direction of the imbalance

An assessment of the hopping strategy and inter-limb asymmetry during the triple hop test: a test–retest pilot study

The aims of the present study are to: (1) determine within- and between-session reliability of multiple metrics obtained during the triple hop test; and (2) determine any systematic bias in both the test and inter-limb asymmetry scores for these metrics. Thirteen male young American football athletes performed three trials of a triple hop test on each leg on two separate occasions. In addition to the total distance hopped, manual detection of touch down and toe-off were calculated via video analysis, enabling flight time (for each hop), ground contact time (GCT), reactive strength index (RSI), and leg stiffness (between hops) to be calculated. Results showed all coefficient of variation (CV) values were ≤ 10.67% and intraclass correlation coefficients (ICC) ranged from moderate to excellent (0.53–0.95) in both test sessions. Intrarater reliability showed excellent reliability for all metrics (CV ≤ 3.60%, ICC ≥ 0.97). No systematic bias was evident between test sessions for raw test scores (g = −0.34 to 0.32) or the magnitude of asymmetry (g = −0.19 to 0.43). However, ‘real’ changes in asymmetry (i.e., greater than the CV in session 1) were evident on an individual level for all metrics. For the direction of asymmetry, kappa coefficients revealed poor-to-fair levels of agreement between test sessions for all metrics (K = −0.10 to 0.39), with the exception of the first hop (K = 0.69). These data show that, given the inherent limitations of distance jumped in the triple hop test, practitioners can confidently gather a range of reliable data when computed manually, provided sufficient test familiarization is conducted. In addition, although the magnitude of asymmetry appears to show only small changes between test sessions, limb dominance does appear to fluctuate between test sessions, highlighting the value of also monitoring the direction of the imbalance

Association between dynamic strength index derived from isometric squat and squat jump or countermovement jump and force-velocity profile

We investigated the associations and differences between dynamic strength index (DSI) calculated from different types of vertical jump (countermovement jump; CMJ and squat jump; SJ) and different isometric knee joint angles (30, 60 and 90°), and associations with force-velocity (FV) profile and its constituent variables (maximal theoretical force (V0), power (Pmax) and velocity (V0) and the slope of the FV relationship (Sfv), on a sample of young athletes and active participants (n = 28). There were moderate associations between Pmax and all DSI values (r=0.42-0.69; p<0.05), V0 and all DSI values from CMJ and DSI30 from SJ (r=0.43-0.56; p<0.05), while Sfv was associated only with DSI30 and DSI90 in CMJ (r=0.40-0.43; p<0.05).This suggest that DSI and FV methods provide similar information and can be used in a similar manner to direct an individual’s training

Asymmetries in Ground Reaction Forces During Turns by Elite Slalom Alpine Skiers Are Not Related to Asymmetries in Muscular Strength

The ground reaction forces (GRF) associated with competitive alpine skiing, which are relatively large, might be asymmetric during left and right turns due to asymmetries in the strength of the legs and torso and the present investigation was designed to evaluate this possibility. While skiing a symmetrical, 20-gate slalom course, the asymmetries of 9 elite alpine skiers were calculated on the basis of measurements provided by inertial motion units (IMU), a Global Navigation Satellite System and pressure insoles. In addition, specialized dynamometers were utilized to assess potential asymmetry in the strength of their legs and torso in the laboratory. In total, seven variables related to GRF were assessed on-snow and eight related to strength of the legs and torso in the laboratory. The asymmetries in these parameters between left and right turns on snow were expressed in terms of the symmetry (SI) and Jaccard indices (JI), while the asymmetries between the left and right sides of the body in the case of the laboratory measurements were expressed as the SIs. The three hypotheses to be tested were examined using multivariable regression models. Our findings resulted in rejection of all three hypotheses: The asymmetries in total GRF (H1), as well as in the GRF acting on the inside and outside legs (H2) and on the rear- and forefeet GRF (H3) during left and right turns were not associated with asymmetries in parameters related to muscular strength. Nevertheless, this group of elite slalom skiers exhibited significant asymmetry between their right and left legs with respect to MVC during ankle flexion (0.53 ± 0.06 versus 0.60 ± 0.07 Nm/kg, respectively) and hip extension (2.68 ± 0.39 versus 2.17 ± 0.26 Nm/kg), as well as with respect to the GRFs on the inside leg while skiing (66.8 ± 7.39 versus 76.0 ± 10.0 %BW). As indicated by the JI values, there were also large asymmetries related to GRF as measured by pressure insoles (range: 42.7–56.0%). In conclusion, inter-limb asymmetries in GRFs during elite alpine skiing are not related to corresponding asymmetries in muscular strength. Although our elite athletes exhibited relatively small inter-limb asymmetries in strength, their asymmetries in GRF on-snow were relatively large.

Effects of 12-week full body resistance exercise on vertical jumping with and without military equipment in Slovenian Armed Forces

Introduction Jumping ability is one of the most important physical qualities in military personnel. Previous training intervention studies have shown equivocal effects on jumping ability. In this study, we assessed the effect of a 12-week resistance exercise programme on countermovement jump (CMJ) performance with and without military equipment. Methods Ninety-six members of the Slovenian Armed Forces (age range 20–47 years) were allocated to the intervention (n=65) and the control (n=32) group. The intervention group performed 2 sessions of full body resistance exercise per week for 12 weeks, while the control group continued with their regular training routine. Before and after the intervention, CMJ assessment using force plates was conducted with and without military equipment. Results CMJ testing with and without equipment both exhibited high to excellent relative and absolute reliability. The intervention elicited statistically significant (p=0.011–0.026; η2=0.05–0.06), but small improvements in CMJ height when performed without equipment (from 28.2±3.8cm to 29.5±3.3cm) and with equipment (from 25.3±3.7cm to 27.1±6.1). Other variables showed even smaller or trivial changes. Conclusions This study suggests that CMJ with equipment could be a reliable tool to assess jumping performance specific to requirements of military work, which would increase the ecological validity of the testing. The present structured full-body training intervention showed modest improvements in jumping ability in both testing conditions. Trial registration number NCT034154

EFFECTS OF CREATINE, GINSENG, AND ASTRAGALUS SUPPLEMENTATION ON STRENGTH, BODY COMPOSITION, MOOD, AND BLOOD LIPIDS DURING STRENGTH-TRAINING IN OLDER ADULTS

The effects of supplemental dietary creatine and a botanical extract consisting of ginseng and astragalus were evaluated in 44 adults aged 55-84 years participating in a 12-week strength-training program. Participants consumed creatine only (Cr), creatine plus botanical extract (CrBE), or placebo (PL), and performed bench press, lat pull down, biceps curl, leg press, knee extension, and knee flexion for 3 sets of 8-12 reps on 3 days per week for 12 weeks. The 1-repetition maximum for each exercise, body composition (full-body DEXA), blood lipids, and mood states were evaluated before and after the intervention. Training improved (p < 0.05) strength and lean mass for all groups, however greater gains were observed with Cr and CrBE compared with placebo (but no difference was found between Cr and CrBE). Only CrBE improved blood lipids and self-reported vigor, and the CrBE group lost significantly more body fat and gained more bench press strength than Cr. These results indicate that strength and lean mass gains achieved by older adults participating in a strength training program can be enhanced with creatine supplementation, and that ginseng and astragalus may provide additional health and psychological benefits. However, these herbs do not appear to have an additive effect on strength and lean mass gains during trainin