Acute exercise performed before and after motor practice enhances the positive effects on motor memory consolidation.

Performing a single bout of exercise can enhance motor learning and long-term retention of motor skills. Parameters such as the intensity and when the exercise bout is performed in relation to skill practice (i.e., timing) likely influence the effectiveness. However, it is still not fully understood how exercise should be administered to maximize its effects and how exercise interacts with distinct components of skill learning. Here, we expand this knowledge by investigating the potential synergistic effects of performing acute exercise both prior to and following motor practice. Sixty-four, able-bodied, young adult male participants practiced a sequential visuomotor accuracy tracking (SVAT) task requiring rapid and accurate force modulation and high levels of precision control using intrinsic hand muscles. The task also contained a repeated pattern of targets that allowed sequence-specific skill improvements. Sequential and non-sequential motor performance was assessed at baseline, immediately after motor practice, and again seven days later. One group performed moderate-intensity exercise before practice (PREMO), a second group performed high-intensity exercise after practice (POSTHI), a third group exercised both before and after practice (PREMO + POSTHI), and a fourth group did not exercise during these periods (CON). Regardless of the exercise condition, acute exercise improved long-term retention of the skill by countering performance decay between experimental sessions (i.e., a 7-day interval). Furthermore, exercising both before and after motor practice led to the greatest improvements in skilled performance over time. We found that the effects of exercise were not specific to the practiced sequence. Namely, the effects of exercise generalized across sequential and non-sequential target positions and orders. This suggests that acute exercise works through mechanisms that promote general aspects of motor memory (e.g., lasting improvements in fast and accurate motor execution). The results demonstrate that various exercise protocols can promote the stabilization and long-term retention of motor skills. This effect can be enhanced when exercise is performed both before and after practice.

Trial-to-trial Variability and Cortical Processing Depend on Recent Outcomes During Human Reinforcement Motor Learning.

The history of our actions and their outcomes represent important information, informing choices and efficiently guiding future behavior. While unsuccessful (S-) outcomes are expected to lead to more explorative motor states and increased behavioral variability, successful (S+) outcomes are expected to reinforce the use of the previous action. Here, we show that humans attribute different values to previous actions during reinforcement motor learning when they experience S- compared to S+ outcomes. Behavioral variability after an S- outcome is influenced more by the previous outcome than after S+ outcomes. Using electroencephalography, we show that theta band oscillations of the prefrontal cortex are most prominent during changes in two consecutive outcomes, potentially reflecting the need for enhanced cognitive control. Our results suggest that S+ experiences 'overwrite' previous motor states to a greater extent than S- experiences and that modulations in neural oscillations in the prefrontal cortex play a potential role in encoding changes in movement variability state during reinforcement motor learning.

Effects of Periodization on Strength and Muscle Hypertrophy in Volume-Equated Resistance Training Programs: A Systematic Review and Meta-analysis.

BACKGROUND: In resistance training, periodization is often used in an attempt to promote development of strength and muscle hypertrophy. However, it remains unclear how resistance training variables are most effectively periodized to maximize gains in strength and muscle hypertrophy. OBJECTIVE: The aims of this study were to examine the current body of literature to determine whether there is an effect of periodization of training volume and intensity on maximal strength and muscle hypertrophy, and, if so, to determine how these variables are more effectively periodized to promote increases in strength and muscle hypertrophy, when volume is equated between conditions from pre to post intervention. METHODS: Systematic searches were conducted in PubMed, Scopus and SPORTDiscus databases. Data from the individual studies were extracted and coded. Meta-analyses using the inverse-variance random effects model were performed to compare 1-repetition maximum (1RM) and muscle hypertrophy outcomes in (a) non-periodized (NP) versus periodized training and (b) in linear periodization (LP) versus undulating periodization (UP). Subgroup analyses examining whether results were affected by training status were performed. Meta-analyses of other periodization model comparisons were not performed, due to a low number of studies. RESULTS: Thirty-five studies met the inclusion criteria. Results of the meta-analyses comparing NP and periodized training demonstrated an overall effect on 1RM strength favoring periodized training (ES 0.31, 95% confidence interval (CI) [0.04, 0.57]; Z = 2.28, P = 0.02). In contrast, muscle hypertrophy did not differ between NP and periodized training (ES 0.13, 95% CI [-0.10, 0.36]; Z = 1.10, P = 0.27). Results of the meta-analyses comparing LP and UP indicated an overall effect on 1RM favoring UP (ES 0.31, 95% CI [0.02, 0.61]; Z = 2.06, P = 0.04). Subgroup analyses indicated an effect on 1RM favoring UP in trained participants (ES 0.61, 95% CI [0.00, 1.22]; Z = 1.97 (P = 0.05)), whereas changes in 1RM did not differ between LP and UP in untrained participants (ES 0.06, 95% CI [-0.20, 0.31]; Z = 0.43 (P = 0.67)). The meta-analyses showed that muscle hypertrophy did not differ between LP and UP (ES 0.05, 95% CI [-0.20, 0.29]; Z = 0.36 (P = 0.72)). CONCLUSION: The results suggest that when volume is equated between conditions, periodized resistance training has a greater effect on 1RM strength compared to NP resistance training. Also, UP resulted in greater increases in 1RM compared to LP. However, subgroup analyses revealed that this was only the case for trained and not previously untrained individuals, indicating that trained individuals benefit from daily or weekly undulations in volume and intensity, when the aim is maximal strength. Periodization of volume and intensity does not seem to affect muscle hypertrophy in volume-equated pre-post designs. Based on this, we propose that the effects of periodization on maximal strength may instead be related to the neurophysiological adaptations accompanying resistance training.

The effect of cathodal transspinal direct current stimulation on tibialis anterior stretch reflex components in humans.

Spinal DC stimulation (tsDCS) shows promise as a technique for the facilitation of functional recovery of motor function following central nervous system (CNS) lesion. However, the network mechanisms that are responsible for the effects of tsDCS are still uncertain. Here, in a series of experiments, we tested the hypothesis that tsDCS increases the excitability of the long-latency stretch reflex, leading to increased excitability of corticospinal neurons in the primary motor cortex. Experiments were performed in 33 adult human subjects (mean age 28 ± 7 years/14 females). Subjects were seated in a reclining armchair with the right leg attached to a footplate, which could be quickly plantarflexed (100 deg/s; 6 deg amplitude) to induce stretch reflexes in the tibialis anterior (TA) muscle at short (45 ms) and longer latencies (90-95 ms). This setup also enabled measuring motor evoked potentials (MEPs) and cervicomedullary evoked potentials (cMEPs) from TA evoked by transcranial magnetic stimulation (TMS) and electrical stimulation at the cervical junction, respectively. Cathodal tsDCS at 2.5 and 4 mA was found to increase the long-latency reflex without any significant effect on the short-latency reflex. Furthermore, TA MEPs, but not cMEPs, were increased following tsDCS. We conclude that cathodal tsDCS over lumbar segments may facilitate proprioceptive transcortical reflexes in the TA muscle, and we suggest that the most likely explanation of this facilitation is an effect on ascending fibers in the dorsal columns.

Reorganization of functional and directed corticomuscular connectivity during precision grip from childhood to adulthood.

How does the neural control of fine movements develop from childhood to adulthood? Here, we investigated developmental differences in functional corticomuscular connectivity using coherence analyses in 111 individuals from four different age groups covering the age range 8-30 y. EEG and EMG were recorded while participants performed a uni-manual force-tracing task requiring fine control of force in a precision grip with both the dominant and non-dominant hand. Using beamforming methods, we located and reconstructed source activity from EEG data displaying peak coherence with the EMG activity of an intrinsic hand muscle during the task. Coherent cortical sources were found anterior and posterior to the central sulcus in the contralateral hemisphere. Undirected and directed corticomuscular coherence was quantified and compared between age groups. Our results revealed that coherence was greater in adults (20-30 yo) than in children (8-10 yo) and that this difference was driven by greater magnitudes of descending (cortex-to-muscle), rather than ascending (muscle-to-cortex), coherence. We speculate that the age-related differences reflect maturation of corticomuscular networks leading to increased functional connectivity with age. We interpret the greater magnitude of descending oscillatory coupling as reflecting a greater degree of feedforward control in adults compared to children. The findings provide a detailed characterization of differences in functional sensorimotor connectivity for individuals at different stages of typical ontogenetic development that may be related to the maturational refinement of dexterous motor control.

Cortical signatures of precision grip force control in children, adolescents, and adults.

Human dexterous motor control improves from childhood to adulthood, but little is known about the changes in cortico-cortical communication that support such ontogenetic refinement of motor skills. To investigate age-related differences in connectivity between cortical regions involved in dexterous control, we analyzed electroencephalographic data from 88 individuals (range 8-30 years) performing a visually guided precision grip task using dynamic causal modelling and parametric empirical Bayes. Our results demonstrate that bidirectional coupling in a canonical 'grasping network' is associated with precision grip performance across age groups. We further demonstrate greater backward coupling from higher-order to lower-order sensorimotor regions from late adolescence in addition to differential associations between connectivity strength in a premotor-prefrontal network and motor performance for different age groups. We interpret these findings as reflecting greater use of top-down and executive control processes with development. These results expand our understanding of the cortical mechanisms that support dexterous abilities through development.

Directed connectivity between primary and premotor areas underlying ankle force control in young and older adults.

The control of ankle muscle force is an integral component of walking and postural control. Aging impairs the ability to produce force steadily and accurately, which can compromise functional capacity and quality of life. Here, we hypothesized that reduced force control in older adults would be associated with altered cortico-cortical communication within a network comprising the primary motor area (M1), the premotor cortex (PMC), parietal, and prefrontal regions. We examined electroencephalographic (EEG) responses from fifteen younger (20-26 â€‹yr) and fifteen older (65-73 â€‹yr) participants during a unilateral dorsiflexion force-tracing task. Dynamic Causal Modelling (DCM) and Parametric Empirical Bayes (PEB) were used to investigate how directed connectivity between contralateral M1, PMC, parietal, and prefrontal regions was related to age group and precision in force production. DCM and PEB analyses revealed that the strength of connections between PMC and M1 were related to ankle force precision and differed by age group. For young adults, bidirectional PMC-M1 coupling was negatively related to task performance: stronger backward M1-PMC and forward PMC-M1 coupling was associated with worse force precision. The older group exhibited deviations from this pattern. For the PMC to M1 coupling, there were no age-group differences in coupling strength; however, within the older group, stronger coupling was associated with better performance. For the M1 to PMC coupling, older adults followed the same pattern as young adults - with stronger coupling accompanied by worse performance - but coupling strength was lower than in the young group. Our results suggest that bidirectional M1-PMC communication is related to precision in ankle force production and that this relationship changes with aging. We argue that the observed differences reflect compensatory reorganization that counteracts age-related sensorimotor declines and contributes to maintaining performance.

Acute Exercise Protects Newly Formed Motor Memories Against rTMS-induced Interference Targeting Primary Motor Cortex.

Acute cardiovascular exercise can promote motor memory consolidation following motor practice, and thus long-term retention, but the underlying mechanisms remain sparsely elucidated. Here we test the hypothesis that the positive behavioral effects of acute exercise involve the primary motor cortex and the corticospinal pathway by interfering with motor memory consolidation using non-invasive, low frequency, repetitive transcranial magnetic stimulation (rTMS). Forty-eight able-bodied, young adult male participants (mean age = 24.8 y/o) practiced a visuomotor accuracy task demanding precise and fast pinch force control. Following motor practice, participants either rested or exercised (20 min total: 3 × 3 min at 90% VO2peak) before receiving either sham rTMS or supra-threshold rTMS (115% RMT, 1 Hz) targeting the hand area of the contralateral primary motor cortex for 20 min. Retention was evaluated 24 h following motor practice, and motor memory consolidation was operationalized as overnight changes in motor performance. Low-frequency rTMS resulted in off-line decrements in motor performance compared to sham rTMS, but these were counteracted by a preceding bout of intense exercise. These findings demonstrate that a single session of exercise promotes early motor memory stabilization and protects the primary motor cortex and the corticospinal system against interference.

Transcranial Alternating Current Stimulation of the Primary Motor Cortex after Skill Acquisition Improves Motor Memory Retention in Humans: A Double-Blinded Sham-Controlled Study.

Consolidation leading to retention of motor memory following motor practice involves activity-dependent plastic processes in the corticospinal system. To investigate whether beta-band transcranial alternating current stimulation (tACS) applied immediately following skill acquisition can enhance ongoing consolidation processes and thereby motor skill retention 20 adults participated in a randomized, double-blinded, sham-controlled study. Participants received tACS at peak beta-band corticomuscular coherence (CMC) frequency or sham tACS for 10 min following practice of a visuomotor ankle dorsiflexion task. Performance was measured as the average percentage time on target. Electroencephalograhy (EMG) was measured at Cz and EMG from the right tibialis anterior muscle. CMC and intramuscular coherence (IMC) were estimated during 2-min tonic dorsiflexion. Motor skill retention was tested 1 and 7 days after motor practice. From the end of motor practice to the retention tests, motor performance improved more in the tACS group compared with the sham tACS group after 1 (P = 0.05) and 7 days (P < 0.001). At both retention tests, beta-band IMC increased in the tACS group compared with post-tACS. Beta-band CMC increased in the tACS group at retention day 1 compared with post-tACS. Changes in CMC but not IMC were correlated with performance 1 and 7 days following practice. This study shows that tACS applied at beta-band CMC frequency improves consolidation following visuomotor practice and increases beta-band CMC and IMC. We propose that oscillatory beta activity in the corticospinal system may facilitate consolidation of the motor skill.

Acute high-intensity football games can improve children's inhibitory control and neurophysiological measures of attention.

Recent studies suggest that a single bout of exercise can lead to transient performance improvements in specific cognitive domains in children. However, more knowledge is needed to determine the key exercise characteristics for obtaining these effects and how they translate into real-world settings. In the present study, we investigate how small-sided football games of either high- or moderate-intensity affect measures of inhibitory control in a school setting. Eighty-one children (mean age 11.8, 48 boys) were randomly allocated to three groups performing 20-minute of high-intensity small-sided real football games (SRF), moderate-intensity small-sided walking football games (SWF) or resting (RF). Behavioral measures of inhibitory control and neurophysiological measures of attention (P300 latency and amplitude) were obtained during a flanker task performed at baseline and 20 minutes following the intervention. Retention of declarative memory was assessed in a visual memory task 7 days after the intervention. Measures of inhibitory control improved more in children performing SRF compared to SWF 19 ms, 95% CI [7, 31 ms] (P = 0.041). This was paralleled by larger increases in P300 amplitudes at Fz in children performing SRF compared both to RF in congruent (3.54 µV, 95% CI [0.85, 6.23 µV], P = 0.039) and incongruent trials (5.56 µV, 95% CI [2.87, 8.25 µV], P < 0.001) and compared to SWF in incongruent trials (4.10 µV, 95% CI [1.41, 6.68 µV], P = 0.010). No effects were found in measures of declarative memory. Together this indicates that acute high-intensity small-sided football games can transiently improve measures of inhibitory control and neurophysiological correlates of attention. Intense small-sided football games are easily implementable and can be employed by practitioners, for example, during breaks throughout the school day.

The effects of aging on cortico-spinal excitability and motor memory consolidation.

We investigated whether cortico-spinal excitability (CSE), a marker of synaptic plasticity, is associated with age-related differences in the consolidation of motor memory. Young and older participants practiced a visuomotor tracking task. Skill retention was assessed 8 and 24 hours after motor practice. Transcranial magnetic stimulation applied over the primary motor cortex at rest and during an isometric muscle contraction was used to assess absolute and normalized to baseline CSE at different points after practice. When skill performance was normalized to baseline level, both groups showed similar gains in acquisition, but the young group showed better retention 24 hours after practice. The young group also showed greater absolute CSE assessed during the isometric muscle contraction. Although young participants with greater absolute CSE showed better skill retention, it was the capacity to increase CSE after motor practice, and not absolute CSE, what was associated with skill retention in older participants. Older adults who have the capacity to increase CSE during motor memory consolidation show a better capacity to retain motor skills.

Acute Exercise and Motor Memory Consolidation: The Role of Exercise Timing.

High intensity aerobic exercise amplifies offline gains in procedural memory acquired during motor practice. This effect seems to be evident when exercise is placed immediately after acquisition, during the first stages of memory consolidation, but the importance of temporal proximity of the exercise bout used to stimulate improvements in procedural memory is unknown. The effects of three different temporal placements of high intensity exercise were investigated following visuomotor skill acquisition on the retention of motor memory in 48 young (24.0 ± 2.5 yrs), healthy male subjects randomly assigned to one of four groups either performing a high intensity (90% Maximal Power Output) exercise bout at 20 min (EX90), 1 h (EX90+1), 2 h (EX90+2) after acquisition or rested (CON). Retention tests were performed at 1 d (R1) and 7 d (R7). At R1 changes in performance scores after acquisition were greater for EX90 than CON (p < 0.001) and EX90+2 (p = 0.001). At R7 changes in performance scores for EX90, EX90+1, and EX90+2 were higher than CON (p < 0.001, p = 0.008, and p = 0.008, resp.). Changes for EX90 at R7 were greater than EX90+2 (p = 0.049). Exercise-induced improvements in procedural memory diminish as the temporal proximity of exercise from acquisition is increased. Timing of exercise following motor practice is important for motor memory consolidation.