Effects of a horizontal speed deceleration training programme on measures of physical fitness in youth male handball players.

This study examined the effects of an 8-week horizontal speed deceleration training (HSDT) programme in combination with regular handball-specific training as compared with handball-specific training only in measures of physical fitness in male youth handball players. Thirty-nine players were randomly assigned to either an HSDT group (n = 18; 15.55 ± 0.24 years) or an active-control group (CG; n = 21; 14.59 ± 0.23 years). The results showed significant and large between-group differences at post-test in countermovement jump, change-of-direction speed, and repeated sprint ability (RSA) (all p < 0.01; d = 2.04 and 1.37, 1.39, 1.53, and 1.53 for the CMJ, 505 CoD, RSAbest, RSAaverage, and RSAtotal performances, respectively). The post-hoc-analysis demonstrated significant and large improvements in all measures of physical fitness in the HSDT group (∆2.49% to 16,25%; d = 1.01 to 1,70; all p < 0,01). The CG, however, failed to reach any significant difference in all measures of physical fitness ((∆0.31% to 1.98%; d = 0.15 to 0.22; p = 0.379; p > 0.05). To summarise, an 8-week in-season HSDT programme alongside regular handball-specific training yielded positive effects on various performance measures including jumping ability, CoD speed, and RSA, when compared to handball-specific training alone. These results highlight the potential benefits of integrating HSDT into the training regimen of youth handball athletes during the competitive season.

Resistance training intervention performed with different muscle action durations influences the maximal dynamic strength without promoting joint-angle specific strength gains.

The present study investigated the effect of 10-week matched (range of motion, volume, intensity, rest, and repetition duration) training protocols with varying muscle action duration (MAD) on maximal voluntary isometric contraction (MVIC) test at eight different knee angles and one-repetition maximum (1RM) test after in seated knee extensor machine. Forty women were allocated into one control and three training groups with varying MAD: 5C1E (5s concentric action [CON] and 1s eccentric action [ECC]), 3C3E (3s CON and 3s ECC), and 1C5E (1s CON and 5s ECC). All training groups (5C1E, 3C3E, and 1C5E) showed a greater relative response in 1RM performance than the control group (0.1 ± 3.5%, p ≤ 0.05). The 1C5E group presented greater relative increases in the 1RM performance (22.1 ± 11.6%) compared to 5C1E (13.6 ± 9.2%; p ≤ 0.05) and 3C3E (14.1 ± 5.5%, p ≤ 0.05) groups. The training groups increased the MVIC performance more than the control group (p ≤ 0.05), although there were no significant differences between the training groups. This study demonstrated that isoinertial resistance training protocols with shorter CON MAD showed greater maximum dynamic strength performance response than matched training protocols with other MAD configurations. However, the configuration of MAD did not induce angle-specificity to increase the maximum isometric strength.

Peak Oxygen Uptake is Slope Dependent: Insights from Ground Reaction Forces and Muscle Oxygenation in Trained Male Runners.

BACKGROUND: The aim of this study is to explore the effect of treadmill slope on ground reaction forces and local muscle oxygenation as putative limiting factors of peak oxygen uptake in graded maximal incremental running tests. Thirteen trained male runners completed five maximal incremental running tests on treadmill at - 15%, - 7.5%, 0%, 7.5% and 15% slopes while cardiorespiratory and local muscle oxygenation responses as well as ground reaction forces were continuously recorded. Blood lactate concentration and isometric knee extensor torque were measured before and after each test. RESULTS: Peak oxygen uptake was lower at - 15% slope compared to all other conditions (from - 10 to - 17% lower, p < 0.001), with no difference between - 7.5 and + 15% slope. Maximal heart rate and ventilation values were reached in all conditions. The negative external mechanical work increased from steep uphill to steep downhill slopes (from 6 to 92% of total external work) but was not correlated with the peak oxygen uptake reduction. Local muscle oxygenation remained higher in - 15% slope compared to level running (p = 0.003). CONCLUSIONS: Similar peak oxygen uptake can be reached in downhill running up to - 7.5% slope. At more severe downhill slopes (i.e., - 15%), greater negative muscle work and limited local muscle deoxygenation occurred, even in subjects familiarized to downhill running, presumably preventing the achievement of similar to other condition's peak oxygen uptake. KEY POINTS: Trained male runners can reach like level running V̇O2peak at moderate but not at severe negative slope. Negative external mechanical work increases with increasing negative slope. At maximal intensity Vastus Lateralis muscle oxygenation is higher in steep negative slope. Knee extensor isometric muscle torque is preserved after maximal level and uphill running, but reduced after downhill running, despite lower blood lactate. Progressive reduction of V̇O2 at maximal effort with increasing negative slope might be related to the metabolic consequences of increased lower limb negative external work (i.e., eccentric muscle actions).

Lessons from the COVID-19 pandemic: Insights into effective training strategies for physical development in football.

Professional soccer players typically perform regular training sessions and match play for most of the yearly macrocycle with limited time focused on solely developing physical development. The COVID-19 outbreak in 2020 caused mass disruption to professional soccer but provided an opportunity for an alternative approach to training in attempt to develop professional soccer players physical fitness levels. In a non-randomised and non-controlled study, we aimed to assess the effectiveness of a 13-week remote based physical training programme on physical fitness levels in elite professional soccer players. Twenty professional soccer players undertook body composition assessments, a countermovement jump (CMJ) test, eccentric hamstring strength test and a submaximal 30-15 intermittent fitness test (IFT) pre- and post-remote based training programme. Body mass (79.3 ± 6.7 vs. 80.0 ± 7.3 kg), skinfold thickness (54.1 ± 14.8 vs. 56.7 ± 15.2 mm), maximum CMJ height (38.4 ± 3.4 vs. 40.9 ± 4.1 cm), eccentric hamstring strength (1035 ± 158 vs. 1009 ± 140 n) and percentage max heart rate reached in submaximal 30-15 IFT (81.3 ± 5.2 vs. 82.3 ± 7.3%) were maintained (all P > 0.05) from pre- to post training programme, respectively. Although team-based soccer specific training load was removed, and the training programmes prescribed had an increased physical focus, fitness levels were maintained. This suggests that alternative modes of training can potentially be used in instances where team-based soccer specific training load isn't required or is unavailable, without negatively impacting physical development.

Repeated measurements of Adaptive Force: Maximal holding capacity differs from other maximal strength parameters and preliminary characteristics for non-professional strength vs. endurance athletes.

The Adaptive Force (AF) reflects the neuromuscular capacity to adapt to external loads during holding muscle actions and is similar to motions in real life and sports. The maximal isometric AF (AFisomax) was considered to be the most relevant parameter and was assumed to have major importance regarding injury mechanisms and the development of musculoskeletal pain. The aim of this study was to investigate the behavior of different torque parameters over the course of 30 repeated maximal AF trials. In addition, maximal holding vs. maximal pushing isometric muscle actions were compared. A side consideration was the behavior of torques in the course of repeated AF actions when comparing strength and endurance athletes. The elbow flexors of n = 12 males (six strength/six endurance athletes, non-professionals) were measured 30 times (120 s rest) using a pneumatic device. Maximal voluntary isometric contraction (MVIC) was measured pre and post. MVIC, AFisomax, and AFmax (maximal torque of one AF measurement) were evaluated regarding different considerations and statistical tests. AFmax and AFisomax declined in the course of 30 trials [slope regression (mean ± standard deviation): AFmax = -0.323 ± 0.263; AFisomax = -0.45 ± 0.45]. The decline from start to end amounted to -12.8% ± 8.3% (p < 0.001) for AFmax and -25.41% ± 26.40% (p < 0.001) for AFisomax. AF parameters declined more in strength vs. endurance athletes. Thereby, strength athletes showed a rather stable decline for AFmax and a plateau formation for AFisomax after 15 trials. In contrast, endurance athletes reduced their AFmax, especially after the first five trials, and remained on a rather similar level for AFisomax. The maximum of AFisomax of all 30 trials amounted 67.67% ± 13.60% of MVIC (p < 0.001, n = 12), supporting the hypothesis of two types of isometric muscle action (holding vs. pushing). The findings provided the first data on the behavior of torque parameters after repeated isometric-eccentric actions and revealed further insights into neuromuscular control strategies. Additionally, they highlight the importance of investigating AF parameters in athletes based on the different behaviors compared to MVIC. This is assumed to be especially relevant regarding injury mechanisms.

Torque-angle curve of the knee flexors in athletes with a prior history of hamstring strain.

OBJECTIVES: To investigate the knee flexor torque-angle curve after hamstring strain injury using different muscle action types and angular velocities. DESIGN: Cross-sectional. SETTING: Controlled laboratory. PARTICIPANTS: Thirteen collegiate athletes injured hamstring strain (21.0 ± 0.8 years; 173.9 ± 6.5 cm; 70.1 ± 10.5 kg). MAIN OUTCOME MEASURES: Concentric and eccentric knee flexor torque was measured at 60 & 300°/sec. Peak torque and average torque every 10° were determined from torque-angle curve and injured side was compared with non-injured side. RESULTS: No significant differences were found in the concentric muscle actions. However, the eccentric peak torque was significantly lower on the injured side at 60°/sec (p = 0.048) and at 300°/sec (p = 0.002). The average eccentric torque was significantly lower on the injured side at 60°/sec from 10° to 20° of knee flexion (p = 0.012-0.018) and at 300°/sec from 10° to 60° of knee flexion (p = 0.005-0.049). CONCLUSION: The knee flexor torque-angle curve changes with eccentric muscle action after hamstring injury. Eccentric torque declines were close to full knee extension at 60°/sec and a wide range of knee flexion at 300°/sec. The assessment and rehabilitation of eccentric hamstring strength may be important to consider the effect of the angular velocity after hamstring strain injury.

Maximal isokinetic elbow and knee flexor-extensor strength measures in combat sports athletes: the role of movement velocity and limb side.

BACKGROUND: Maximal isokinetic strength ratios of joint flexors and extensors are important parameters to indicate the level of muscular balance at the joint. Further, in combat sports athletes, upper and lower limb muscle strength is affected by the type of sport. Thus, this study aimed to examine the differences in maximal isokinetic strength of the flexors and extensors and the corresponding flexor-extensor strength ratios of the elbows and knees in combat sports athletes. METHOD: Forty male participants (age = 22.3 ± 2.5 years) from four different combat sports (amateur boxing, taekwondo, karate, and judo; n = 10 per sport) were tested for eccentric peak torque of the elbow/knee flexors (EF/KF) and concentric peak torque of the elbow/knee extensors (EE/KE) at three different angular velocities (60, 120, and 180°/s) on the dominant and non-dominant side using an isokinetic device. RESULTS: Analyses revealed significant, large-sized group × velocity × limb interactions for EF, EE, and EF-EE ratio, KF, KE, and KF-KE ratio (p ≤ 0.03; 0.91 ≤ d ≤ 1.75). Post-hoc analyses indicated that amateur boxers displayed the largest EE strength values on the non-dominant side at ≤ 120°/s and the dominant side at ≥ 120°/s (p < 0.03; 1.21 ≤ d ≤ 1.59). The largest EF-EE strength ratios were observed on amateur boxers' and judokas' non-dominant side at ≥ 120°/s (p < 0.04; 1.36 ≤ d ≤ 2.44). Further, we found lower KF-KE strength measures in karate (p < 0.04; 1.12 ≤ d ≤ 6.22) and judo athletes (p ≤ 0.03; 1.60 ≤ d ≤ 5.31) particularly on the non-dominant side. CONCLUSIONS: The present findings indicated combat sport-specific differences in maximal isokinetic strength measures of EF, EE, KF, and KE particularly in favor of amateur boxers on the non-dominant side. TRIAL REGISTRATION: This study does not report results related to health care interventions using human participants and therefore it was not prospectively registered.

Electromyographic Assessment of the Lower Leg Muscles during Concentric and Eccentric Phases of Standing Heel Raise.

Only a small number of muscle activation patterns from lower limbs have been reported and simultaneous muscle activation from several lower limb muscles have not yet been investigated. The purpose of this study was to examine any gender differences in surface electromyography (EMG) activity from six recorded lower limb muscles of the dominant limb at baseline (i.e., with the foot placed flat on the floor and in the neutral position), and during concentric and eccentric phases when performing a heel raise task. In total, 10 females and 10 males performed a standing heel raise task comprising of three continuous phases: baseline, unloading (concentric muscle action), and loading (eccentric muscle action) phases. Muscle activation from six muscles (gastrocnemius medialis, gastrocnemius lateralis, soleus, tibialis anterior, peroneus longus, and peroneus brevis) were measured using the Myon 320 EMG System. Root mean squared values of each muscle were calculated for each phase. Descriptive and inferential statistics were incorporated into the study. Statistically significant p values were set at 0.05. The results showed no significant differences between baseline, concentric, and eccentric phases with respect to each of the muscles investigated. Except for the gastrocnemius medialis at baseline and concentric phases, no significant differences were observed between genders or contractions. The data suggests that gender does not significantly influence the eccentric phase during the standing heel raise task.

Residual force enhancement in humans: Is there a true non-responder?

When an active muscle is stretched and kept isometrically active, the resulting force is enhanced compared to a purely isometric reference contraction at the same muscle length and activity; a generally accepted muscle property called residual force enhancement (rFE). Interestingly, studies on voluntary muscle action regularly identify a significant number of participants not showing rFE. Therefore, the aim was to unmask possible confounders for this non-responsive behavior. Ten participants performed maximum voluntary isometric plantarflexion contractions with and without preceding stretch. Contractions were accompanied by the assessment of voluntary activation using the twitch-interpolation technique. The same test protocol was repeated four additional times with a least on day rest in-between. Additionally, at the first and fifth sessions, a submaximal tetanic muscle-stimulation condition was added. At both muscle-stimulation sessions mean rFE higher 10% (p < 0.028) was found. In contrast, during voluntary muscle action, individual participants showed inconsistent rFE across sessions and only one session (#3) had significant rFE (5%; p = 0.023) in group means. As all participants clearly had rFE in electrical stimulation conditions, structural deficits cannot explain the missing rFE in voluntary muscle action. However, we also did not find variability in voluntary activation levels or muscle activity as the confounding characteristics of "non-responders."

Assessment of the Adaptive Force of Elbow Extensors in Healthy Subjects Quantified by a Novel Pneumatically Driven Measurement System with Considerations of Its Quality Criteria.

Adaptive Force (AF) reflects the capability of the neuromuscular system to adapt adequately to external forces with the intention of maintaining a position or motion. One specific approach to assessing AF is to measure force and limb position during a pneumatically applied increasing external force. Through this method, the highest (AFmax), the maximal isometric (AFisomax) and the maximal eccentric Adaptive Force (AFeccmax) can be determined. The main question of the study was whether the AFisomax is a specific and independent parameter of muscle function compared to other maximal forces. In 13 healthy subjects (9 male and 4 female), the maximal voluntary isometric contraction (pre- and post-MVIC), the three AF parameters and the MVIC with a prior concentric contraction (MVICpri-con) of the elbow extensors were measured 4 times on two days. Arithmetic mean (M) and maximal (Max) torques of all force types were analyzed. Regarding the reliability of the AF parameters between days, the mean changes were 0.31-1.98 Nm (0.61%-5.47%, p = 0.175-0.552), the standard errors of measurements (SEM) were 1.29-5.68 Nm (2.53%-15.70%) and the ICCs(3,1) = 0.896-0.996. M and Max of AFisomax, AFmax and pre-MVIC correlated highly (r = 0.85-0.98). The M and Max of AFisomax were significantly lower (6.12-14.93 Nm; p ≤ 0.001-0.009) and more variable between trials (coefficient of variation (CVs) ≥ 21.95%) compared to those of pre-MVIC and AFmax (CVs ≤ 5.4%). The results suggest the novel measuring procedure is suitable to reliably quantify the AF, whereby the presented measurement errors should be taken into consideration. The AFisomax seems to reflect its own strength capacity and should be detected separately. It is suggested its normalization to the MVIC or AFmax could serve as an indicator of a neuromuscular function.

Evidence for Muscle Cell-Based Mechanisms of Enhanced Performance in Stretch-Shortening Cycle in Skeletal Muscle.

Force attained during concentric contraction (active shortening) is transiently enhanced following eccentric contraction (active stretch) in skeletal muscle. This phenomenon is called stretch-shortening cycle (SSC) effect. Since many human movements contain combinations of eccentric and concentric contractions, a better understanding of the mechanisms underlying the SSC effect would be useful for improving physical performance, optimizing human movement efficiency, and providing an understanding of fundamental mechanism of muscle force control. Currently, the most common mechanisms proposed for the SSC effect are (i) stretch-reflex activation and (ii) storage of energy in tendons. However, abundant SSC effects have been observed in single fiber preparations where stretch-reflex activation is eliminated and storage of energy in tendons is minimal at best. Therefore, it seems prudent to hypothesize that factor(s) other than stretch-reflex activation and energy storage in tendons contribute to the SSC effect. In this brief review, we focus on possible candidate mechanisms for the SSC effect, that is, pre-activation, cross-bridge kinetics, and residual force enhancement (RFE) obtained in experimental preparations that exclude/control the influence of stretch-reflex activation and energy storage in tendons. Recent evidence supports the contribution of these factors to the mechanism of SSCs, and suggests that the extent of their contribution varies depending on the contractile conditions. Evidence for and against alternative mechanisms are introduced and discussed, and unresolved problems are mentioned for inspiring future studies in this field of research.

EMG ANALYSIS OF UPPER EXTREMITY MUSCLES DURING ISOKINETIC TESTING OF THE SHOULDER JOINT / 体力科学

<b>Purpose</b> : This study was to investigate the patterns of electromyography (EMG) amplitude responses during maximal, eccentric muscle action with shoulder adduction and diagonal movement, at 6 different positions on the dynamometer.<b>Methods</b> : The participants for this investigation were 9 males and 5 females. Testing consisted of each subject performing eccentric muscle exercise of the dominant shoulder muscle at a velocity of 60°/sec and 180°/sec. Muscle activity values was recorded individually from six different muscles and peak torque values were extracted for each test from torque curves once. EMG data were normalized to the highest root mean square (RMS), and were expressed as a % maximum voluntary isometric contraction (%MVIC).<b>Results</b> : The posterior parts of upper extremity muscle complex generate overall high muscle activity (> 40%MVIC) during all testing for eccentric muscle activity with diagonal shoulder movement. Posterior deltoid (PD), upper trapezius (UT), and middle trapezius (MT) muscles show differences between eccentric muscle action with shoulder adduction and eccentric muscle action with diagonal shoulder movement.<b>Conclusion</b> : The present results show that an improved understanding of muscle activity patterns during different movement may benefit many fields of athletic trainers, coaches, and athletes, in addition to assisting in injury prevention for throwers, and even rehabilitation after injury.