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Whether visuomotor plasticity of postural control is a trainable feature in older age remains an open question despite the wealth of visually guided exercise games promising to improve balance skill. We asked how aging affects adaptation and learning of a visual feedback (VF) reversal during visually guided weight shifting and whether this skill is modulated by explicit knowledge. Twenty-four older (71.43 + 2.54 years) and 24 young (24.04 1 0.93 years) participants were exposed to a 180° VF reversal while tracking a horizontally moving target by voluntarily weight shifting between two force platforms. An explicit strategy was available to half of the participants with detailed instruction to counter the VF rotation. Individual error data were fitted to an exponential function to assess adaptation. Fewer older (12/24) than younger (21/24) participants adapted to the VF reversal, displaying error curves that fitted the exponential function. Older adults who adapted to the VF reversal (responders. n= 12) reached an asymptote in performance in the same weight shifting cycle and displayed a similar mean asymptotic error compared with young participants. Young but not older responders exhibited an aftereffect when the VF reversal was removed. Instruction did not influence spatial error modulations regardless of age. The large individual variations within the older adults' group during early adaptation suggest age-specific limitations in using explicit cognitive strategies when older adults are exposed to an abrupt mirror feedback reversal that requires a change in weight shifting direction during whole-body postural tracking. [ABSTRACT FROM AUTHOR]

The aim of our study was to compare the effects of two different plyometric training programs (targeting knee extensors or plantar flexors) on jump height and strength of leg muscles. Twenty‐nine male basketball players were assigned to the knee‐flexed (KF), knee‐extended (KE), or control groups. In addition to regular training, the KF group performed plyometric jumps (10 sets of 10 jumps, 3 sessions/week, 4 weeks) from 50 cm boxes with the knee flexed (90°–120°), whereas the KE group performed the jumps from 30 cm boxes with the knee much more extended (130°–170°). Jumping ability was evaluated with squat jumps (SJs), countermovement jumps (CMJs), and drop jumps from 20 cm (DJ20) and 40 cm (DJ40). Knee and ankle muscles were assessed during maximal isokinetic and isometric tests, and EMG activity was recorded from vastus lateralis and medial gastrocnemius. The KF group increased SJ (+10%, d = 0.86) and CMJ (+11%, d = 0.70) but decreased DJ40 height (−7%, d = −0.40). Conversely, the KE group increased DJ20 (+10%, d = 0.74) and DJ40 (+12%, d = 0.77) but decreased SJ height (−4%, d = −0.23). The reactivity index during DJs increased (+10% for DJ20, d = 0.47; +20% for DJ40, d = 0.91) for the KE group but decreased (−10%, d = −0.48) for the KF group during DJ40. Plantar flexor strength increased for the KE group (d = 0.72–1.00) but not for the KF group. Negative transfer across jumps is consistent with the principle of training specificity. Basketball players interested to perform fast rebounds in their training should avoid plyometric jumps with large knee flexions and long contact times. Highlights: Plyometric training specificity: different jump techniques (knee flexed vs. knee extended) elicited specific adaptations in jumping performance. Training with the knees flexed improved squat jump and countermovement jump height, whereas training with the knees extended augmented drop jump height.Negative transfer: the different jump techniques can have a negative influence on jump height and reactivity index. Drop jump height declined after knee‐flexed training, whereas squat jump height decreased after knee‐extended training.Plyometric training exercises should be aligned with sport‐specific movements to optimize performance. Basketball players who perform fast, powerful movements should avoid plyometric jumps with large knee flexions and long contact times. [ABSTRACT FROM AUTHOR]

Introduction: The aim of the study was to compare maximal force, force steadiness, and the discharge characteristics of motor units in the tibialis anterior (TA) muscle during submaximal isometric contractions for ankle dorsiflexion and adduction of the foot. Methods: Nineteen active young adults performed maximal and submaximal isometric dorsiflexion and adduction contractions at five target forces (5%, 10%, 20%, 40%, and 60% maximal voluntary contraction [MVC]). The activity of motor units in TA was recorded by high-density EMG. Results: The maximal force was similar between dorsiflexion and adduction, despite EMG amplitude for TA being greater (P < 0.05) during dorsiflexion than adduction. The coefficient of variation (CV) for force (force steadiness) during dorsiflexion was always less (P < 0.05) than during adduction, except of 5% MVC force. No differences were observed for mean discharge rate; however, the regression between the changes in discharge rate relative to the change of force was significant for dorsiflexion (R² = 0.25, P < 0.05) but not for adduction. Discharge variability, however, was usually less during dorsiflexion. The CV for interspike interval was less (P < 0.05) at 10%, 20%, and 40% MVC but greater at 60% MVC during dorsiflexion than adduction. Similarly, the SD values of the filtered cumulative spike train of the motor units in TA were less (P < 0.05) at 5%, 10%, 20%, and 40% MVC during dorsiflexion than adduction. Conclusions: Although the mean discharge rate of motor units in TA was similar during foot adduction and ankle dorsiflexion, discharge variability was less during dorsiflexion resulting in less accurate performance of the steady adduction contractions. The neural drive to bifunctional muscles differs during their accessory function, which must be considered for training and rehabilitation interventions. [ABSTRACT FROM AUTHOR]

Our study aimed to investigate the relationship between the strength of ankle muscles and postural sway in older adults during upright standing tasks of varying difficulty. Forty-three elderly participants (20 women) performed maximal isometric contractions and three distinct postural tasks: normal quiet stance (60 s), tandem stance (20 s), and one-legged stance (10 s) on a pressure platform. Postural sway was comprehensively assessed, considering center of pressure velocity, peak-to-peak amplitude, and standard deviation of center of pressure displacement in both anterior/posterior and medio/lateral directions. Additionally, weight distribution asymmetry in both directions served as a quantifiable index. Surface electromyographic (EMG) activity of the Tibialis Anterior, Medial Gastrocnemius, Rectus Femoris, and Semitendinosus was recorded during the postural tasks. Throughout the balance tasks, isometric plantar and dorsiflexion torque exhibited a consistent decrease as posture variables increased (p < 0.001). Narrowing the base of support led to significant increases in all postural variables and EMG activity (p < 0.01), with a more pronounced effect on ankle muscles compared to hip muscles (p < 0.0005). In the normal quiet stance (r = .683) and tandem stance (r = .641), greater center of pressure velocity correlated with a more symmetrical weight distribution between the legs. These results suggest that ankle muscle strength serves as a reliable predictor of static balance control, particularly in postures involving a narrow stance. Therefore, the enhancement of plantar flexors and dorsiflexors, rather than an exclusive focus on symmetrical weight distribution, is more likely to contribute to improved static balance control in older adults. [ABSTRACT FROM AUTHOR]

The Achilles tendon functions as a load-bearing component crucial for movement performance and swiftly adapts to changes in body mass and strength, particularly during periods of growth spurts. Mechanical and morphological attributes of the Achilles tendon were assessed in 41 participants (20 boys and 21 girls, comprising 22 athletes and 19 nonathletes) over a span of 18 months, employing ramped isometric plantar flexion. Longitudinal variations were analyzed using linear mixed modeling. This longitudinal study aimed to explore the combined effects of sport participation, maturation, and sex on the mechanical characteristics of the Achilles tendon across various muscle-tendon lengths. While the rate of stiffness increase post peak height velocity was comparable across all groups, a noteworthy finding was that boy-athletes displayed a more pronounced and earlier rate of Achilles tendon stiffness augmentation twelve months prior to PHV. Additionally, a distinctive mechanical property alteration was identified solely in boy-athletes at the 0° ankle angle. This elevation in Achilles tendon stiffness among boy-athletes was linked to greater peak force of the plantar flexors and a reduction in elongation. In summary, our study introduces novel longitudinal evidence indicating that sport participation interacts with sex and maturation, yielding a distinct adaptive response in Achilles tendon stiffness, specifically observed at the neutral position. These findings suggest a nuanced adaptive model wherein elevated force levels preceding PHV instigate heightened mechanical loading in specific muscle-tendon lengths, thereby inducing increased stiffness throughout adolescence. Specifically, the Achilles tendon stiffness exhibited a more substantial rate of increase in athletes compared to nonathletes and girls, leading to the conclusion that boyathletes represent a distinct population during the maturation process. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the influence of sprint training on muscle and tendon properties across different developmental stages, specifically focusing on pre-adolescent children, adolescent boys, and young men. It is well-established that adults show higher force production, rate of force development, and effective re-use of elastic energy during the stretch-shortening cycle (SSC) compared to children due to different muscle and tendon properties. Thus, it is important to classify the interaction between age and the training process on muscle-tendon system. Participant's tendon properties were assessed using two 10 seconds ramp isometric contractions (increasing the force level every 2") with an ultrasound probe stabilized on muscle-tendon junction. Moreover, two maximal isometric plantar flexions were performed to evaluate maximal isometric force. Both force capacity and tendon stiffness was evaluated. Our results showed significant increases in height, body mass, and strength levels through maturation (p<0.05). Moreover, significant changes were found in tendon stiffness and produced force in athletes compared with non-athletes groups (p<0.05). On the other hand, significant differences were found in relative stiffness and force between young adults and non-athletes with the athletes (p<0.05). Our results revealed that both maturity and sprint training imposes the tendons to a greater mechanical load through the higher produced force and strain. These stimuli lead to adaptive responses and changes in Achilles tendon properties. Moreover, our data support the importance of training in young adults to maintain tendon properties at the level of adolescence. This study provides valuable insights into the interaction between age, sprint training, and tendon adaptations to prevent tissue imbalances in male individuals engaged in sports activities. [ABSTRACT FROM AUTHOR]

The aim of the study was to evaluate the difference on force fluctuations during isometric plantar flexion (PF) and dorsiflexion (DF) and the potential influence of changes in ankle joint angle. Twelve young adults performed 2 maximal voluntary contractions (MVC) and 3 steady submaximal isometric contractions at three ankle angles (70o, 90o and 110o) and five target forces (5, 10, 20, 40 and 60% MVC) with both the plantar flexors and dorsiflexors. The electromyographic (EMG) activity of Medial Gastrocnemius (MGAS), Soleus (SOL) and Tibialis Anterior (TA) was recorded. MVC force was greater during PF compared to DF for all ankle angles (p > 0.05). The normalized amplitude (coefficient of variation, CoV) of the force fluctuations was similar between PF and DF. However, the absolute amplitude (standard deviation) was higher during PF compared to DF, regardless of ankle angle and target force (p < 0.05). The CoV for force exhibited a gradual decrease from 5% to 20% MVC, and then it plateaued at 40% and 60% MVC force. During plantar flexion, the normalized EMG amplitude (root mean square) of the agonists MGAS and SOL increased progressively from 5% to 60% MVC force (p > 0.05), as the same happened with the TA during DF. These findings indicate that muscle groups with large differences in maximal force production are likely to have the same force steadiness during submaximal contractions, apparently because the neural activation of agonist and antagonist muscles has common features. [ABSTRACT FROM AUTHOR]

The postural sway during tasks of increasing difficulty and the isokinetic and isometric strength of knee extensors-flexors and ankle plantar flexors-dorsiflexors muscles were evaluated through ages. Sixty participants (27 women) were divided in 5 age groups (group 1: 21-30 years, group 2: 31-40 years, group 3: 41-50 years, group 4: 51-60 years and group 5: 61-75 years). They performed 3 static balance tasks with the eyes open and closed on a force plate: Normal Quiet Stance (30 s), Tandem Stance (20 s), and One Leg Stance (10 s). Posture was quantified using several Center of Pressure (CoP) variables in Anterior/Posterior and Medio/Lateral direction). They also performed maximal isokinetic and isometric knee extensions-flexions and plantar flexionsdorsiflexions. The CoP velocity increased gradually from group 1 to group 5. When narrowing the base of support, the CoP excursion increased for all age groups (P<0.05). Knee and ankle muscles strength decreased gradually from group 1 to group 5. During all postural tasks, moderate (-0.39 to -0.61) correlations between CoP velocity and isometric strength of knee and ankle muscles were observed. Knee and ankle strength can be considered as predictors of static balance control, especially when postural requirements relate to narrower stance. [ABSTRACT FROM AUTHOR]

Normal gait development has been widely investigated due to the importance of locomotion for independent daily living. Understanding gait control and its process is fundamental, especially in critical developmental periods, for effective interventions. However, less is known about longitudinal changes in walking patterns between adolescent boys and girls, who experience an accelerated increase in both height and weight, causing low gross motor coordination. Here, to address this literature gap, we evaluated the effect of maturity and walking speed in Vertical Ground Reaction Forces (VGRF) and time gait parameters, in twenty-three boys (age 12.5 ± 0.29) and twenty-two girls (age 10.5 ± 0.32). They performed normal and fast pace at their self-selected speed, at 18 and 9 months before peak height velocity (PHV) and at PHV. We quantified the magnitudes of the three VGRF: first peak (Fzmax1), second peak (Fzmax2), and valley (Fzmin), along with total contact time (ts), and gait variability in anterior-posterior (AP) and mediolateral (ML) directions. A mixed model of repeated measure analysis of variance (RM ANOVA) revealed significant effects of maturity and walking speed in VGRF, ts, and variability. Girls exhibited a steadier walking pattern than boys, with lower Fzmax1 and ts, since variability decreased values near PHV for both sexes. In summary, gait is a still maturing process in early adolescents, significantly influenced by walking speed. Growth spurt affects in a different way gait patterns of adolescent boys and girls. The data from this study could be used as a reference for educators and trainers, planning adolescent interventions and preventing injuries. [ABSTRACT FROM AUTHOR]

In 2019-2020 and 2020-2021, the COVID-19 pandemic led to unexpected behavioral restrictions, allowing only the individual training of the athletes. The purpose of the present study was to record the effects of a home-based training program on physical performance at a semi-professional level, after the Covid-19 confinement, in terms of external load. Twenty soccer players from one semi-professional team participated in this study. The data was collected by GPS devices, with an accelerometer and gyroscope, and a sampling rate 10Hz. The external load is evaluated by the total distance, the high-intensity runs, the sprint distance as well as the number of accelerations and decelerations. Three matches before and twelve games after the lockdown were analyzed and compared. During the confinement period, the players performed 5-6 training sessions per week. This period lasted over 4 four months. The training sessions were monitored by a free smartphone application. Similarly, the players communicated with the technical staff with a free internet application. The results showed significant increases (p < 0.05) in the total distance covered during the matches after the intervention. No significant increase in highintensity runs and the number of accelerations were found (p > 0.05). The present data suggest that an intervention monitored by a free application could improve athletic performance at the semi-professional level, even after long-term abstinence from team training such as quarantine or off-season periods. These data might provide affordable solutions to the semi-professional soccer teams, which could be used during the off-season period leading to reduce detraining effects and higher performance in the forthcoming championship. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the effects of ankle-specific plyometric exercises and electromyostimulation (EMS) on vertical jump biomechanics. Thirty participants were divided into three training groups: a) incline plyometrics group, b) plane plyometrics group and c) EMS group. Each group followed a 4 weeks training period. The plyometric training session consisted of eighty vertical hops as fast as the participants could while EMS training included eighty fast contractions in 15° plantar flexion. Take-off velocity (Vto) and sagittal kinematics of the hip, the knee, and the ankle joints were recorded and analyzed. The kinetics data were also analyzed before and after the intervention. The muscle activity of the medial gastrocnemius (MGAS) and the co-activation index between the Tibialis Anterior (TA) and the MGAS was recorded and evaluated during CMJ before and after training. A non-significant effect of training on Vto, sagittal kinematics, and muscle activity was observed for the training groups after the training period. In contrast, all the intervention groups were found to increase ground reaction forces and rate of force development significantly during the CMJ. Coactivation index was increased after plane plyometrics and EMS training for CMJ in contrast to the incline hopping. The present results indicate that specific ankle training could result in alterations of the dynamic parameters as well as in muscle co-activation during the CMJ after a four-week intervention. These changes do not include increases in the kinematics or vertical performance. The present results suggest that a longer training period is needed to observe significant changes in vertical jumping technique and performance. [ABSTRACT FROM AUTHOR]

This study examined the post-activation potentiation (PAP) effects on squat jump (SJ) performance and on peak rate of force development (RFDpeak) in preadolescent (10--12 y), adolescents (14--15 y) and adults (20--25 y) males and females. All participants performed a SJ with and without prior conditioning stimulus (PAP and control protocol, respectively), consisting of 3 × 3-second maximal isometric squats. Jump height and RFDpeak of the vertical ground reaction force during SJ were assessed before, and at 20 seconds and at 4 minutes following the conditioning stimulus. The results revealed a different pattern of age-effect on SJ performance within males and females. The RFDpeak significantly increased as a factor of age in both males and females (P < .05). Increase in SJ performance after conditioning stimulus occurred only in men (P < .05), with no effects in teen-males, boys, and female groups. There was a significant PAP effect on RFDpeak in both adult groups (P < .05) and teen-males, with no effects in children. In conclusion, the PAP effects on SJ performance and RFDpeak are age- and sex-dependent; that is PAP appears as a viable method for acutely enhancing SJ performance in men but not in pediatric population. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the differences in muscle architecture during isometric tests between children and adults. Eight boys (age= 11.2 ± 0.26 years) and eight men (age= 22.3 ± 2.01 years) performed plantar flexion isometric efforts at angles of -15°, 0°, 15° at 0%, 40%, 60%, 80% of MVC. Analysis of variance tests indicated that adults showed greater fascicle length from rest to 80% of MVC (p < .05), greater pennation angle at 80% and 100% of MVC (p < .05) and greater aponeuroses displacement at levels of effort greater than 60% of MVC (p < .05). These differences observed in MG would appear to favor better utilization of the force-length and the force-velocity relationships, of the muscle in adults compared with children. [ABSTRACT FROM AUTHOR]

The aim of our study was to compare the force steadiness and the discharge characteristics of motor units in the tibialis anterior (TA) during ankle dorsiflexion and foot adduction produced by submaximal isometric contractions with the dominant and non-dominant foot. Fifteen young men performed maximal and submaximal contractions at five target forces with both legs, and motor unit activity in TA was recorded using high-density electromyography. Maximal force and the fluctuations in force during submaximal contractions were similar between the two legs (p > 0.05). Motor unit activity was characterized by measures of mean discharge rate (MDR), coefficient of variation for interspike interval (CoV for ISI), and standard deviation of the filtered cumulative spike train (SD of fCST). There were no statistically significant differences in motor unit activity between legs during ankle dorsiflexion. In contrast, the MDR and the CoV for ISI but not the SD of fCST, were greater for the non-dominant foot compared with the dominant foot during foot adduction. Nonetheless, these differences in motor unit activity were not sufficient to influence the force fluctuations during the submaximal contractions. These results indicate that control of the force produced by TA during the two actions was not influenced by limb dominance. [ABSTRACT FROM AUTHOR]