Isokinetics and Exercise Science

Although subjects with forward head/rounded shoulders posture (FHRSP) may exhibit changes in scapular position and periscapular muscle strength relative to normal subjects, few studies have investigated this.

We compared scapular position and periscapular muscle strength between subjects with and without FHRSP.

In total, 50 subjects with FHRSP and 50 normal subjects were included. The craniovertebral angle (CVA) and rounded shoulder angle (RSA) were measured to determine FHRSP. To compare scapular position, scapular protraction, elevation, upward rotation, and anterior tilt were measured. To compare periscapular muscle strength, the strengths of the upper trapezius, middle trapezius, lower trapezius, and serratus anterior were measured using an isometric hand-held dynamometer.

Relative to normal subjects, those with FHRSP had elevated, protracted, and anteriorly tilted scapulae and significantly weaker middle trapezius, lower trapezius, and serratus anterior (p<0.05). Both CVA and RSA showed negative correlations with protraction, anterior tilt of the scapula; they showed moderate positive correlations with scapular elevation. The strengths of the middle trapezius, lower trapezius, and serratus anterior muscles were moderately correlated with CVA and RSA (p<0.05).

Relative to normal subjects, those with FHRSP exhibited changes in scapular position and periscapular muscle deficits. This information will be useful for designing exercise programs for individuals with FHRSP.

Although an imbalance between the thoracic and lumbar erector spinae muscle activity is known to contribute to spinal dysfunction, the factors influencing this muscle balance, particularly thoracic extension mobility, remain unclear.

This study investigated the associations of thoracic kyphosis and thoracic extension mobility with erector spinae muscle activity and muscle balance.

Ninety-four healthy participants underwent measurements of thoracic kyphosis angle, thoracic extension angle, and erector spinae muscle activity (longissimus thoracis, iliocostalis lumborum pars thoracis, and iliocostalis lumborum pars lumborum). Muscle balance was assessed using the ratios of longissimus thoracis to iliocostalis lumborum pars lumborum and iliocostalis lumborum pars thoracis to iliocostalis lumborum pars lumborum. Regression analyses were conducted with erector spinae muscle activities and their ratios as independent variables, and thoracic kyphosis and thoracic extension as dependent variables.

Regression analyses showed that the ratio of longissimus thoracis to iliocostalis lumborum pars lumborum and the activity of the iliocostalis lumborum pars thoracis significantly predicted thoracic extension mobility (adjusted R² = 0.14, p < 0.001), while the activity of the iliocostalis lumborum pars lumborum significantly predicted thoracic kyphosis (adjusted R² = 0.04, p = 0.026).

These findings suggest that the assessment and intervention of thoracic extension mobility may be significantly associated with the erector spinae muscle balance during trunk extension exercises.

Glenohumeral internal rotation range of motion deficit (GIRD) is linked to shoulder strength in the glenohumeral (GH) joint and to increased risk of throwing-related injuries. In adolescent overhead athletes, GIRD ≥25° has been associated with a four-fold higher risk of upper-extremity injury. However, from a functional perspective relevant to overhead throwing, the extent to which GIRD is related to the dynamic strength of the shoulder rotators has not been investigated.

This study compared internal rotation (IR) and external rotation (ER) torque between adolescent baseball athletes with and without GIRD, and examined factors associated with concentric and eccentric IR/ER torque, including GH joint range of motion (ROM).

Eighty male adolescent baseball athletes participated. IR, ER, total rotational ROM, and GIRD were measured. Concentric and eccentric torque of IR and ER, as well as functional strength ratios, were assessed. Group differences were analyzed with independent t-tests, correlations with Pearson's coefficients, and predictors with Stepwise multiple regression analysis.

Concentric IR and ER torques were significantly lower in the GIRD group than in the non-GIRD group (mean differences: 4.6% and 6.9% body weight, respectively; p < 0.05). Concentric torques showed poor to fair correlations with GH joint rotational ROM, particularly reduced IR ROM and increased GIRD. Eccentric torques did not differ significantly between groups. Regression analysis identified IR ROM and GIRD as significant predictors of concentric torque, while antagonist exhibited the greatest relative influence on the agonist.

Concentric shoulder strength (IR and ER torques) is reduced in adolescent baseball athletes with GIRD and is significantly associated with IR ROM loss. IR ROM and GIRD were key predictors of concentric torque, while antagonist strength exerted the greatest relative influence on agonist function. In contrast, eccentric torques showed no group differences or meaningful correlation with GH joint ROM.

There is limited knowledge about the relationships between concentric and eccentric lower-limb strength and sprint, change-of-direction (CoD), and forward or lateral jump performance in elite youth soccer players.

This study investigated the associations between knee strength and sprinting, CoD, and single-leg jump performance in youth soccer players (mean age = 16 years; n = 41).

Maximal isokinetic knee extension and flexion strength (60°/s and 180°/s) and Nordic hamstring strength were assessed and correlated with single-leg forward hop and side-bounce distance, 10 m and 30 m sprint times, and 90° and 180° CoD test times.

Pearson correlations revealed task- and leg-specific relationships. Stronger knee extensors at 60°/s were associated with faster 90° CoD performance, whereas stronger knee flexors and higher flexion-to-extension ratios at 180°/s were linked to faster 10 m and 30 m sprints. When the right leg acted as the inside turning leg, greater knee flexor strength (180°/s) was related to slower 180° CoD performance but faster 10 m and 30 m sprint times. When the right leg acted as the outside leg: (i) higher flexion-to-extension ratios (60°/s) corresponded to slower 90° CoD performance; (ii) stronger knee flexors (180°/s) with slower 180° CoD; and (iii) higher strength ratios at 180°/s with slower 90° and 180° CoD performance. No significant associations were found for the left leg or single-leg jump tests.

These findings highlight the movement- and limb-specific nature of lower-limb strength contributions in youth soccer players. Overall, hamstring strength supported sprint performance, whereas quadriceps strength underpinned CoD ability.

This cross-sectional study aimed to investigate how different hip abduction angles influence hip abduction torque and muscle activation of the gluteus medius (Gmed) and tensor fasciae latae (TFL) during side-lying hip abduction in individuals with Gmed weakness.

Twenty-five individuals with Gmed weakness participated in this study. Participants performed isometric hip abduction in a side-lying position at four joint angles (−15°, 0°, 15°, and 30°). Hip abduction torque was measured using an isokinetic dynamometer, while surface electromyography was used to simultaneously record Gmed and TFL muscle activities. The Gmed/TFL activity ratio was calculated to examine relative activation patterns. Hip abduction torque was normalized to body weight.

Peak hip abduction torque was greatest at −15°, followed by 0°, 15°, and 30°. Electromyographic analysis showed that Gmed activity was greater at −15° and 0° than at 30°, whereas TFL activity was lowest at 30°. Although no significant pairwise differences were detected, the Gmed/TFL activity ratio tended to increase with increasing hip abduction angle, reaching its highest value at 30°.

Hip abduction angle influences hip abduction torque and muscle activation during side-lying hip abduction in individuals with Gmed weakness. A more adducted starting position was associated with greater torque, whereas a more abducted position showed lower TFL activity and higher Gmed/TFL ratios; thus, hip abduction angle may be considered in rehabilitation, with caution.

Data from 206 physically active individuals (basketball players and students) were retrospectively analyzed. Hierarchical multiple regression models predicted jump height, with sex and training status entered as covariates, followed by braking RFD and braking FI, and finally the early-to-late push-off FI ratio. Additional models examined whether braking variables predicted the FI ratio.

In bilateral CMJ, braking variables and the FI ratio significantly improved model fit beyond sex and training status, with the FI ratio emerging as a strong independent predictor of jump height (lower early-to-late push-off FI ratio: β = −0.367, p < 0.001). Braking FI was positively associated with jump height (β = 0.165, p = 0.003), and braking RFD also showed a positive independent association in the final model (β = 0.197, p < 0.001). In unilateral CMJ, the FI ratio similarly predicted jump height (lower ratio: β = −0.311, p < 0.001), whereas braking RFD was not independently associated and braking FI showed a modest positive effect (β = 0.154, p = 0.009). Braking RFD positively predicted the FI ratio in both jump tasks, indicating an association with a more early-loaded push-off profile.

Jump height was consistently related to push-off force distribution, with relatively greater late-phase FI (i.e., a lower early-to-late ratio) associated with superior performance. Braking FI showed modest positive associations with jump height, whereas braking RFD primarily influenced push-off force distribution and displayed task-dependent relevance for performance.

This study evaluated the construct validity of the inertial-load protocol, the New Power Bike Test (NPBT), by comparing it with the Wingate Anaerobic Test (WAnT) and examining its correlation with criterion measures, including Vertical Jump (VJ) and Isokinetic Leg Strength (ILS).

Thirty-seven healthy adults performed the standard 30-s WAnT and the NPBT (four 4-s maximal accelerations against inertial resistance) in a randomized and counterbalanced crossover design. Data were analyzed using paired t-tests with Cohen's d effect sizes, Pearson and Spearman rank correlations with 95% confidence intervals, Bland–Altman analysis, and Williams’ test for comparing dependent overlapping correlation coefficients.

The NPBT produced significantly higher mean peak power (976.18 W; 11.47 W·kg⁻¹) than the WAnT (705.67 W; 8.34 W·kg⁻¹). Also, the NPBT demonstrated significant correlations with both VJ (r = 0.666 to 0.766, p < 0.001) and ILS (r = 0.638 to 0.861, p < 0.001). In contrast, the WAnT showed weak associations with VJ and inconsistent relationships with ILS (r = 0.240 to 0.663). Bland–Altman analysis confirmed that the protocols are not interchangeable at the individual level (bias = 270.52 W; 95% LoA: −193.02 to 734.05 W). Williams’ test showed that NRPP correlated significantly more strongly than WRPP with all five criterion variables (all p ≤ 0.031).

The NPBT and WAnT are not interchangeable assessment tools. The NPBT provides greater concurrent validity for evaluating instantaneous peak neuromuscular power, likely due to its ability to facilitate force-velocity auto-optimization and specifically target the phosphagen energy system. The WAnT remains appropriate for assessing anaerobic capacity and fatigue tolerance.

This study aimed to examine how muscle strength and balance in adolescent recreational football players were affected by FIFA 11+ (11+). Study design: Randomized controlled study.

The research comprised 24 football players from a team in an amateur league(age: 16.3 ± 0.8 years; height: 176.9 ± 7.3 cm; body mass: 67.3 ± 8.7 kg; BMI: 21.4 ± 1.9 kg/m²). The experimental group (N = 13) had three applications of the 11 + each week for nine weeks. The usual warm-up was continued by the control group (N = 11). The footballers underwent isokinetic and Star Excursion Balance Tests (SEBT) both before and after an intervention.

Prior to the intervention, the experimental group's right hamstring-to-quadriceps (H/Q) strength ratio at 60 °/sec was significantly higher than that of the control group (p = 0032). Following the intervention, there was no difference between the groups (p > 0,05). After training at 240 °/sec, only the left quadriceps peak torque value of the experimental group was significantly higher compared to the control group (101.2 ± 21.4 vs. 85.8 ± 10.7 Nm, p = 0.042). In the comparisons of the groups after the intervention, the experimental group in SEBT was found to be significantly higher (85.4 ± 9.9 vs. 78.0 ± 6.7 cm, p = 0.040) in the right anteromedial aspect while there were no differences between the groups in the other aspects (p > 0,05). In SEBT, assessments of the within-groups before and after the intervention revealed a significant difference in nearly every aspect between the control group and the experimental group (p < 0,05).

The FIFA 11 + program appears to be more effective in improving dynamic balance than isokinetic muscle strength in adolescent amateur soccer players. These findings suggest that while FIFA 11 + may enhance neuromuscular control, additional strength-focused training may be required to elicit substantial strength gains in this population.

FIFA11 + is a widely used programme on adolescent football players, and understanding effects on balance and muscle strength can help to understand efficiency of the programme for injury prevention at early ages.