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Šarabon, N, Kozinc, Ž, and Bishop, C. A comparison of vertical and horizontal reactive strength index variants and association with change of direction performance. J Strength Cond Res37(1): 84–90, 2023—This study sought to investigate the interrelationship between different vertical and horizontal variants of reactive strength index (RSI) and change of direction (CoD) performance. Thirty-one male volleyball players (age: 22.4 ± 3.9 years) performed bilateral drop jumps (DJs), bilateral and unilateral countermovement jumps (CMJs), and triple hops for distance. The RSI was calculated as the ratio of jump height and contact time (DJ), jump height and time to takeoff (CMJ), flight time or hop distance and contact time (triple hop), and 505 CoD test. Reactive strength index obtained from DJ and CMJ tasks exhibited excellent trial-to-trial reliability (intraclass correlation coefficient [ICC] = 0.91–0.94), whereas 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 interlimb asymmetry direction between RSI from unilateral CMJ and triple hop RSI variables was slight to moderate (kappa coefficient = 0.06–0.36). In conclusion, although interrelationships between RSI variants were moderate to high, the direction of interlimb asymmetry was inconsistent, highlighting the notion of movement variability in limb dominance.

The aim of the study was to investigate the differences in bilateral and unilateral dynamic strength index (DSI) between age categories (seniors and juniors), player positions (guards and forwards), its variation during the basketball season, and its association with sprint and change of direction (CoD) performance. Highly trained basketball players (n= 32) performed bilateral and unilateral countermovement jumps (CMJ), bilateral and unilateral isometric squats, 10-m sprint, and 505 CoD test. DSI was calculated from CMJ and isometric peak force, while 10-m sprint and 505 test were used to calculate the CoD deficit. Two-way factorial analysis showed larger isometric peak force in seniors, and larger bilateral DSI in juniors, while guards had higher DSI values and larger peak force in both metrics compared to forwards. Two-way mixed model ANOVA showed a significant increase in unilateral isometric squat and CMJ peak force force (g= –0.08 to –0.64) and increase in bilateral DSI values. Post-hoc analysis showed that isometric squat force significantly increased only in seniors (g= 0.88), resulting in decreased bilateral DSI values (g= 0.52), with bilateral and unilateral DSI values increasing in juniors. Similar trends were observed in guards and forwards, with guards exhibiting a more pronounced increase in all variables compared to forwards. Furthermore, correlation analysis for in-season testing showed moderate associations between isometric squat peak force and CoD ability (r= –0.43 to –0.54; P< 0.001), and weak associations between DSI and CoD ability (r= 0.36 to 0.39; P< 0.05), while associations were not significant for sprint performance. The relationships were lower or absent during pre-season testing. Further interventional studies are needed to determine the usefulness of DSI to guide training related decision-making.

Purpose. The aim of this article was to evaluate the effects of cycle and treadmill desks on energy expenditure and cardiovascular and biochemical indicators in sedentary workers. Materials and methods. In February 2018, six databases were searched. Both parallel and crossover design studies evaluating workplace cycle and treadmill desks compared to a conventional seated condition were included. Results. Twenty-two studies met the inclusion criteria. Cycle and treadmill desks significantly increased energy expenditure (standard mean difference [SMD] = 3.84, p < 0.001, I2 = 95%) and the heart rate (SMD = 1.68, p < 0.001, I2 = 91%), and lowered blood glucose and insulin levels (SMD = –0.54, p < 0.001, I2 = 0% and SMD = –3.13, p < 0.001, I2 = 76%, respectively). The interventions had no effect on blood pressure and other biochemical indicators. Conclusion. Cycle and treadmill desks may positively influence energy expenditure in sedentary workers and could be effective for reducing negative effects of workplace-related sedentary behaviour. However, considerable heterogeneity is present in the measuring protocols for energy expenditure.

Team sports involve various sprinting actions, including curvilinear sprints, yet their neuromuscular factors have been understudied. The aim of this cross-sectional study was to investigate the relationship between lower limb muscle strength, strength asymmetries, linear sprint and curvilinear sprint performance. At two visits 12 male (age: 24.8 ± 4.7 years, height: 1.82 ± 0.06 m, body mass: 80 ± 6.58 kg) and 6 female (age: 20.8 ± 1.33 years, body height: 1.60 ± 0.02 m, body mass: 55.3 ± 2.88 kg) student-athletes completed isometric strength measurements of the knee flexors (KF), knee extensors (KE), hip abductors (HABD), hip adductors (HADD), as well as linear sprint and curvilinear sprint to the right and left. Sprint split times over 30 m (t30) were measured and curvilinear sprint split time deficits (t30deficit) and inter-limb strength asymmetries were calculated. Very large negative correlations were observed between HADDand HABDstrength on one side and t30of curvilinear sprint to the left (r= −0.75 and −0.71; p< 0.001) and right (ρ= −0.81 and −0.70; p< 0.001) on the other. The regression model consisting of HADD, HABD, and KFexplained 76% and 67% of the variance in left and right curvilinear sprint t30, respectively. Similarly, 59% of the left curvilinear sprint t30deficitvariance was explained by the HABDand KFstrength. High inter-limb HABDstrength symmetry was related to better left and right curvilinear sprint t30(r= 0.71 and ρ = 0.75, p< 0.001). These results highlight the pivotal role of hip strength for curvilinear sprint speed, and emphasize the need of symmetrical HABDmuscle strength to optimize neuromuscular function during curvilinear sprint.

The hydraulic resistance device (HRD), a state-of-the-art device developed primarily for resisted sprint training, lacks exploration of its force-generating properties. This technical note aims to evaluate these properties in vitro. In a laboratory experiment, the HRD was pulled with a motorised winch at four speeds (1–4 m s−1) and 12 different HRD resistance levels (low, medium and high). The resistance force induced by the HRD was measured using a force plate mounted under the device, and calculated as mean horizontal force produced at a constant pulling speed. Resistance force repeatability between pulling speeds at specific resistance levels was assessed using the coefficient of variation (CV) whereas the intraclass correlation coefficient (ICC3,1) was calculated to determine the consistency. A linear regression model quantified resistance force as a function of HRD resistance level. Accuracy of the model was assessed using root mean square error (RMSE). Across 12 resistance levels, the HRD produced resistance forces ranging from 22.57 ± 4.84 to 164.57 ± 4.84 N. The CV decreased from 21.5% at the lowest resistance to 0.4% at the highest. The HRD produced resistance force with high consistency (ICC3,1CI = 0.990–0.999). The linear regression model showed a near-perfect fit (R2= 0.99) and predicted resistance force more accurately at medium and high resistance (RMSE range = 0.97–4.57 N). The HRD provides favourable force-generating properties for resisted sprint training and testing, warranting further studies on its exploration in vivo.

The objective of SPEXOR project is to address low back pain as one of the most appealing health problems of the modern society by creating a body of scientific and technological knowledge in the multidisciplinary areas of biomechanics, robotics, and computer science that will lead to technologies for low back pain prevention. In this paper we provide an overview of the current state-of-art of SPEXOR that the consortium achieved in the first twenty-four months of the project. After introducing the rationale, we describe the biomechanics of low back pain intervention, development of the musculoskeletal stress monitoring for assessment of neuromuscular trunk functions, modeling and optimization of the interaction of spinal exoskeleton with the human body, electromechanical design and development of the passive spinal exoskeleton and its control, and finally the end-user evaluation of the functional effects, usability and satisfaction.

•Postural sway demonstrated no difference between manipulation and sham treatment.•Sacroiliac manipulation did not disturb balance as rambling or center of pressure showed no significant change.•Sacroiliac manipulation increased trembling frequency and velocity in the manipulation group.•Balance changes were shown to be minor with SI manipulation and may be compensated by ankle strategy.

This study aimed to determine the within- and between-session reliability of different variables collected during the starting block phase with the KiSprint force starting block and to identify the number of trials that maximise the reliability of the measurement. Thirty high-level sprinters (23 men and 7 women) completed two sessions separated by 1 week. The first session consisted of two sets of five sprints and the second session of one set of five sprints. Outcomes of each set were calculated as Aver3 (average of the first three sprints), Aver5 (average of the five sprints) and CENTRAL (average of the three central sprints). The instrumented sprint starting blocks (KiSprint system) served to record a total of 20 push-off variables. Within-session reliability was acceptable (coefficient of variation (CV)<15%; intraclass correlation coefficient >0.70) for 103 out of 117 comparisons and between-session reliability was acceptable for 60 out of 117 comparisons. Aver5 provided a lower CV (within-session: 4.8% ± 2.9%; between-session: 13.0% ± 6.4%) than Aver3 (within-session: 8.2% ± 6.6% (CV ratio = 1.72); between-session: 14.5% ± 7.1% (CV ratio = 1.11)) and CENTRAL (within-session: 5.3% ± 3.6% (CV ratio = 1.10); between-session: 15.2% ± 9.7% (CV ratio = 1.17)). These results indicate that the KiSprint system can collect several variables with acceptable reliability in high-level sprinters, while the Aver5 procedure is recommended to maximise the reliability of the measurement.

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