Isokinetics and Exercise Science

It is important to devise a method to promote prolonged effect of static stretching (SS) exercise in sports settings. There is also a need to clarify the usefulness of additional short-term SS exercise and examine the results under conditions close to sports settings.

This study aimed to clarify whether or not the prolonged effect of a 30-s static stretching exercise could be maintained for a longer period by performing an additional short-term (15-s) SS exercise following a 15-min rest.

The participants were 15 healthy recreationally active adult males (22.5 ± 1.1 years) who underwent three conditions: 1) SS condition (30-s SS exercise only); 2) SS + 15-s condition (30-s SS and 15-s SS exercise during the rest period); and 3) noSS + 15-s condition (15-s SS exercise only). The knee flexion range of motion (ROM), pain pressure threshold (PPT), and tissue hardness were measured before (PRE), immediately after (POST), and 15 min after the first SS exercise.

There were significant interaction effects in all variables, and post-hoc tests showed that knee flexion ROM and PPT increased significantly, and tissue hardness decreased significantly immediately afterwards in the SS and SS + 15-s conditions. In addition, in the SS + 15-s and noSS + 15-s conditions, the 15-min values were significantly higher than the PRE values (Cohen's d = 0.64 and 0.18, respectively). Moreover, in the SS + 15-s condition, the 15-min value was significantly higher than the PRE value (d = 0.40). Tissue hardness showed a significant decrease immediately afterwards in both the SS and SS + 15-s conditions (d = −0.47 and −0.37). In addition, in the SS + 15-s and noSS + 15-s conditions, the 15-min value was significantly lower than the PRE value.

These results suggest that a 30-s SS exercise followed by an additional short-term SS exercise after a 15-min rest can prolong the changes in muscle passive properties.

Traditional set (TS) and drop set (DS) training modalities differentially affect muscle fatigue and proprioception. Excessive fatigue may compromise proprioceptive function, thereby increasing injury susceptibility. Comparative analysis of TS and DS effects can facilitate training optimization for enhanced performance and safety.

This study aimed to compare the acute effects of traditional set and drop set training methodologies on fatigue levels and proprioceptive sensory mechanisms in bodybuilders.

Twenty-eight male bodybuilders (mean age: 25.53 ± 2.68 years) were randomly allocated to two groups: traditional set (TS, n = 14) and drop set (DS, n = 14). Fatigue was assessed using myotonometric measurements of the pectoralis major (PM), triceps brachii (TB), and deltoid (D) muscles, while proprioceptive accuracy was evaluated using a laser-based angle replication test for shoulder flexion (SF), shoulder abduction (SA), elbow flexion (EF), and wrist flexion (WF).

Both training methodologies induced muscle fatigue and compromised proprioception; however, the deleterious effects of traditional sets were more pronounced. The results demonstrated that the TS group exhibited greater fatigue and more substantial proprioceptive disruption compared to the DS group in the following parameters: PM (u = −1.956; d = 0.84; p = 0.05), TB (t = 2.237; d = 0.84; p = 0.034), SF (t = 2.577; d = 0.97; p = 0.016), EF (u = −1.562; d = 0.68; p = 0.118), and WF (u = −3.033; d = 1.07; p = 0.002) (p < 0.05).

Drop set training may represent a more efficacious method for reducing fatigue while maintaining proprioceptive accuracy, constituting a suitable approach for athletes and coaches seeking to optimize performance and minimize injury risk.

clinicaltrials.gov, (NCT06688552)

https://clinicaltrials.gov/study/NCT06688552?term=NCT06688552&rank=1

Football is a sport that requires both aerobic and anaerobic performance with dynamic movements. Lower extremity injuries are common, especially in the ankle and foot, where foot pronation is a frequent biomechanical issue that can impair balance and performance.

This study aimed to evaluate the effects of foot core exercises and arch-supported insoles on balance and vertical jump performance in elite football players.

Thirty elite male football players with foot pronation deformity were randomly assigned to two groups: Insole Group (IG, n = 15), using only arch-supported insoles, and Insole + Exercise Group (IEG, n = 15), combining insoles with structured foot core exercises for four weeks. Assessments included Navicular Drop Test (NDT), Y-Balance Test, Flamingo Balance Test, Vertical Jump Test, and Visual Analogue Scale (VAS). Pre- and post-test comparisons were analyzed using paired t-tests or Wilcoxon tests, and time × group effects were examined with repeated measures ANOVA.

Significant improvements were observed in both groups for NDT, balance, and vertical jump performance (p < 0.05). The IEG group showed superior gains in NDT and greater pain reduction. Additionally, vertical jump performance showed a near-significant trend favoring the IEG group (p = 0.059).

Combining structured foot exercises with arch-supported insoles results in better outcomes for balance, pronation control, and jump performance compared to insoles alone. These findings support incorporating foot-specific exercises into rehabilitation for footballers with pronation.

ClinicalTrials.gov NCT05821803

URL: https://clinicaltrials.gov/study/NCT05821803

In the triple jump event, the explosive power, coordination, and specialized performance of lower limb muscles are key factors determining athletes’ performance. However, traditional high load resistance training has limitations in improving athletes’ lower limb coordination and sustained explosive power.

The main purpose of the study is to investigate the training effect of low-load resistance combined with single-leg pressurized exercise method on athletes’ lower limb muscle explosive power, coordination, and special performance.

For the study, twenty male triple jumpers were enlisted and split into ten-person experimental and control groups at random. The training effects of conventional single-leg high load resistance training and low-load resistance mixed with single-leg compression training were compared using the experimental approach. The experimental duration was 8 weeks. Before and after the experiment, the athletes’ lower limb muscle circumference, body composition, lower limb dynamic balance ability, isokinetic strength, counter movement jump, one repetition maximum squats, key performance indicators of lower limb explosive power, and triple jump special scores were tested.

After an eight-week training period, the experimental group showed significantly greater improvement than the control group across key performance metrics. Specifically, the experimental group showed superior gains in lower limb muscle circumference, dynamic balance, isokinetic peak torque, and maximum power in the countermovement jump (p < 0.05). Furthermore, their 1RM squat strength and triple jump performance were also significantly enhanced.

It shows that the low-load resistance combined with single-leg pressurization exercise method can effectively improve the athletes’ lower limb explosive power, coordination, and special performance. This provides a reliable lower limb explosive power training program for athletes and coaches.

The stretch-shortening cycle enhances muscle efficiency and force output by, among others, utilizing elastic energy stored in tendons during muscle stretching, but the level of mechanical efficiency is influenced by the intensity of the stretch.

This study aimed to investigate the effects of stretch load and stretching velocity on mechanical efficiency during stretch-shortening cycle contractions.

Ten recreationally active young women performed quadriceps SSC contractions under different stretch loads (20 J to 100 J) and knee flexion angular velocities ( 30 ∘ ⋅ s − 1 and 210 ∘ ⋅ s − 1 ) on an isokinetic dynamometer. Muscle activation of the vastus lateralis and rectus femoris was recorded using electromyography (EMG), and mechanical efficiency was calculated as the ratio of positive to total work.

Results showed that mechanical efficiency decreased with increasing stretch load, with a 17% reduction in mechanical efficiency observed from 20 J to 100 J, accompanied by a threefold increase in knee flexion angle. Although both stretch load and knee flexion angular velocity showed a significant effect on mechanical efficiency (p < 0.05), stretch load had a more substantial impact than knee flexion angular velocity. EMG analysis showed that vastus lateralis EMG activity was consistently higher during stretching phase of stretch shortening cycle contractions compared to knee extension across all conditions, particularly at lower knee flexion angular velocities.

These findings highlight the influence of both stretch load and knee flexion angular velocity on stretch-shortening cycle performance, suggesting that optimal stretch load and knee joint angular velocity combinations can enhance mechanical efficiency and muscle-tendon efficiency in stretch-shortening cycle based movements.

Training safely is important for maintaining healthy locomotion and thus high quality of life into the later years. There is a dearth of information on the sex differences of performing different weight training techniques.

This study aimed to investigate sex differences in lower limb muscle activation during inclined leg press exercise under three biomechanical conditions: (1) stance width (standard vs. wide), (2) load intensity (30% vs. 70% 1RM), and (3) contraction phase (concentric vs. eccentric). A secondary objective was to explore within-sex differences in muscle activation patterns across these conditions.

For this study we recruited 18 healthy young adults (male: 9, female: 9) and each participant performed inclined leg press in two stance conditions (standard and wide) at two load conditions (30% and 70% of the estimated 1 repetition maximum). Muscle activation of six major muscles of the dominant leg was measured by electromyography and normalized integrated EMG (% IEMG) was calculated. A significant level of P<0.05 was applied to investigate any statistical differences.

Muscular activation in males tends to be greater during wide stance than standard whereas no such effect of stance was observed in females. The change in stance from standard to wide, significantly increased activation of vastus medialis muscles only in males at higher loads. The increase in load significantly increased muscle activation of vastus lateralis in a wide stance in both groups.

In this study we specified the differences in muscle activation between women and men which can provide a guideline for maximizing muscular stimulation and reducing sex specific joint loading.

There is insufficient evidence regarding the acute effects of warm-up with dynamic stretching (DS) and static stretching (SS) on children.

The aim of this study was to explore how two common warm-up protocols—DS and SS—acutely influence muscle architecture and key physical performance, including explosive strength and flexibility, in children.

Twenty-one healthy children (age: 10.6 ± 0.73 years) voluntarily participated in this study. Each participant completed two warm-up sessions on separate days, consisting of 3 min of light jogging followed by either a DS or SS protocol. Assessments included biceps femoris muscle architecture (fascicle length, pennation angle and muscle thickness), 50-meter sprint (SPR50m), standing long jump (SLJ), and sit-and-reach (SR) tests. All variables were measured at four time points: before stretching, immediately after stretching, and at 10- and 30-min post-stretching.

Results showed an increase in SPR50m, SLJ, and SR performance after warm-up with DS, lasting for 10 min (p < 0.01). SPR50m, SLJ, and muscle pennation angle decreased after SS (p < 0.05), while SR and muscle fascicle length increased (p < 0.05). Immediately after warm-up, SR and muscle fascicle length were higher in SS than DS (p < 0.05), while SPR50m, SLJ, and pennation angle were lower in SS (p < 0.01).

Similar to adults, warm-up with DS is more suitable for activities that require explosive power and strength in children. In contrast, when the primary goal is to improve flexibility, warm-up with SS can be selectively used. Therefore, the selection of warm-up stretching for children should be guided by the specific performance demands of the subsequent activities

Maximal kicking performance relies heavily on the coordinated involvement of the hip flexors and knee extensors, yet exercises that specifically target these muscle groups are rarely prioritized in soccer training regimens.

This study aimed to examine the effects of a leg-kicking exercise program (LKE) on the kicking speed, sprint performance, and agility of young players.

Thirty-nine youth players were randomly assigned to either an LKE group (n = 18; 15.9 ± 0.9 years) or a control group (n = 21; 15.8 ± 0.6 years). The LKE group performed a leg-kicking exercise three days a week. The participants underwent body composition analysis, isometric knee, isokinetic knee and hip strength tests, maximal ball speed, linear sprint, and agility tests at baseline and post-intervention.

In the LKE group, muscle mass, maximal ball speed in both legs, and both isometric and isokinetic strength significantly increased (p < 0.05), while agility and sprint performance showed no significant changes (p > 0.05).

A 6-week LKE program, in addition to soccer training, may enhance kicking speed in youth players. The LKE may serve as a practical alternative to traditional strength training for improving muscle strength and kicking performance.

In taekwondo, sufficient kicking force is required to score valid points on electronic protectors. Impact force varies with kicking speed, and lower extremity strength is crucial for optimal scoring.

To investigate the relationship between isokinetic strength and segmental acceleration in the striking leg during roundhouse kicks (RHKs).

Seventeen female taekwondo athletes (age: 208 ± 1.81 years) participated. Lower limb isokinetic strength was assessed with a dynamometer, and segmental accelerations were measured using inertial sensors. Correlations between isokinetic moments and accelerations during mid-level and high-level RHKs were analyzed using Fisher's Z transformation.

During mid-level RHKs, knee flexion moments correlated with ankle accelerations, while high-level RHKs showed additional correlations between hip flexion moments and segmental accelerations. Joint accelerations were driven by flexor moments (hip and knee flexion). No bilateral differences were found in isokinetic strength or segmental accelerations, except for ankle acceleration during high-level RHKs (p = 0.039). Significant increases in segmental accelerations (p < 0.05) strengthened by Fisher Z transformation, particularly for knee flexion and ankle acceleration (p < 0.05).

Mid-level RHKs are knee-dominant, while head-level kicks require greater contributions from both knee and hip flexion. Strengthening both extensor and flexor muscles is vital for optimizing kicking performance