Effects of training on postural control and agility when wearing socks of different compression levels

Study aim: The aim of this study was to evaluate the effects of training while wearing socks differing in compression level (clinical, sub-clinical, regular) on performance of static and dynamic balancing and agility tasks in healthy, physically active people. We sought to understand whether socks with different compression properties supported postural regulation and agility task performance by enhancing somatosensory perception, unskewed by specific age range effects. Material and methods: Participants comprised 61 adults aged 18-75 years, divided into three groups (two experimental groups wearing clinical or sub-clinical level compression socks, and one control group wearing regular non-compression socks during training). An 8-week (2 × 1h per week) intervention programme was administered to train static and dynamic balance and postural control, leg strength and agility. Results: A mixed model ANOVA revealed no differences in static and dynamic balance and postural control and agility performance between clinical, sub-clinical, and control groups before and after training. All groups significantly improved their test performance, suggesting that training had some benefit on motor performance. Conclusions: These results raised interesting questions requiring further investigation to examine the effects of wearing socks (with and without different levels of compression) on motor behaviours in specific groups of elderly vs. young participants, in physically active vs. less physically active people, and in performance settings outside standardized laboratory tests to study applications in natural performance environments

Neuromuscular adaptations to short-term high-intensity interval training in female ice hockey players

High-intensity interval training (HIIT) related neuromuscular adaptations, changes in force production and on-ice performance were investigated in female ice-hockey players during pre-season. Fourteen Finnish championship level ice hockey players (average age 22 +/- 3 years) participated in 21/2-week HIIT. Both spinal (H-reflex) and supraspinal (V-wave) neuromuscular responses of the soleus muscle were recorded before and after the training period. Static jump (SJ) and countermovement jump (CMJ) heights, plantar flexor maximal voluntary contraction (MVC) and rate of force development (RFD) were measured. In addition, soleus and tibialis anterior muscles activations (electromyography; EMG) were measured during MVC and RFD tests. During on-ice training, skating speed and acceleration tests were performed. Subjects significantly improved their plantarflexion MVC force (11.6 +/- 11.2%, p < 0.001), RFD (15.2 +/- 15.9%, p < 0.01) and SJ (4.8 +/- 7.6%, p < 0.05). Voluntary motor drive to the soleus muscle (V-wave amplitude) increased by 16.0 +/- 15.4% (p < 0.01) and co-activation of tibialis anterior muscle during the plantar flexion RFD test was reduced by -18.9 +/- 22.2% (p < 0.05). No change was observed in spinal [alpha]-motoneuron excitability (H-reflex) during MVC or in on-ice performance. These results indicate that HIIT can be used to improve athletes' capability to produce maximal and explosive forces, likely through enhanced voluntary activation of their muscles and reduced antagonist co-activation. Therefore, HIIT can be recommended in pre-season training to improve neuromuscular performance. However, a longer than 21/2-week HIIT period is needed to improve on-ice performance in female ice-hockey players.Peer reviewe

Modulation of H-reflex and V-wave responses during dynamic balance perturbations

Motoneuron excitability is possible to measure using H-reflex and V-wave responses. However, it is not known how the motor control is organized, how the H-reflex and V-wave responses modulate and how repeatable these are during dynamic balance perturbations. To assess the repeatability, 16 participants (8 men, 8 women) went through two, identical measurement sessions with ~ 48 h intervals, where maximal isometric plantar flexion (IMVC) and dynamic balance perturbations in horizontal, anterior–posterior direction were performed. Soleus muscle (SOL) neural modulation during balance perturbations were measured at 40, 70, 100 and 130 ms after ankle movement by using both H-reflex and V-wave methods. V-wave, which depicts the magnitude of efferent motoneuronal output (Bergmann et al. in JAMA 8:e77705, 2013), was significantly enhanced as early as 70 ms after the ankle movement. Both the ratio of M-wave-normalized V-wave (0.022–0.076, p < 0.001) and H-reflex (0.386–0.523, p < 0.001) increased significantly at the latency of 70 ms compared to the latency of 40 ms and remained at these levels at latter latencies. In addition, M-wave normalized V-wave/H-reflex ratio increased from 0.056 to 0.179 (p < 0.001). The repeatability of V-wave demonstrated moderate-to-substantial repeatability (ICC = 0.774–0.912) whereas the H-reflex was more variable showing fair-to-substantial repeatability (ICC = 0.581–0.855). As a conclusion, V-wave was enhanced already at 70 ms after the perturbation, which may indicate that increased activation of motoneurons occurred due to changes in descending drive. Since this is a short time-period for voluntary activity, some other, potentially subcortical responses might be involved for V-wave increment rather than voluntary drive. Our results addressed the usability and repeatability of V-wave method during dynamic conditions, which can be utilized in future studies.peerReviewe

Modulations of corticospinal excitability following rapid ankle dorsiflexion in skill- and endurance-trained athletes

Purpose Long-term sports training, such as skill and endurance training, leads to specific neuroplasticity. However, it remains unclear if muscle stretch-induced proprioceptive feedback influences corticospinal facilitation/inhibition differently between skill- and endurance-trained athletes. This study investigated modulation of corticospinal excitability following rapid ankle dorsiflexion between well-trained skill and endurance athletes. Methods Ten skill- and ten endurance-trained athletes participated in the study. Corticospinal excitability was tested by single- and paired-pulse transcranial magnetic stimulations (TMS) at three different latencies following passive rapid ankle dorsiflexion. Motor evoked potential (MEP), short-latency intracortical inhibition (SICI), intracortical facilitation (ICF), and long-latency intracortical inhibition (LICI) were recorded by surface electromyography from the soleus muscle. Results Compared to immediately before ankle dorsiflexion (Onset), TMS induced significantly greater MEPs during the supraspinal reaction period (~ 120 ms after short-latency reflex, SLR) in the skill group only (from 1.7 ± 1.0 to 2.7 ± 1.8%M-max, P = 0.005) despite both conditions being passive. ICF was significantly greater over all latencies in skill than endurance athletes (F (3, 45) = 4.64, P = 0.007), although no between-group differences for stimulations at specific latencies (e.g., at SLR) were observed. Conclusion The skill group showed higher corticospinal excitability during the supraspinal reaction phase, which may indicate a “priming” of corticospinal excitability following rapid ankle dorsiflexion for a supraspinal reaction post-stretch, which appears absent in endurance-trained athletes.peerReviewe

Corticospinal Adaptation to Short-Term Horizontal Balance Perturbation Training

Sensorimotor training and strength training can improve balance control. Currently, little is known about how repeated balance perturbation training affects balance performance and its neural mechanisms. This study investigated corticospinal adaptation assessed by transcranial magnetic stimulation (TMS) and Hoffman-reflex (H-reflex) measurements during balance perturbation induced by perturbation training. Fourteen subjects completed three perturbation sessions (PS1, PS2, and PS3). The perturbation system operated at 0.25 m/s, accelerating at 2.5 m/s2 over a 0.3 m displacement in anterior and posterior directions. Subjects were trained by over 200 perturbations in PS2. In PS1 and PS3, TMS and electrical stimulation elicited motor evoked potentials (MEP) and H-reflexes in the right leg soleus muscle, at standing rest and two time points (40 ms and 140 ms) after perturbation. Body sway was assessed using the displacement and velocity of the center of pressure (COP), which showed a decrease in PS3. No significant changes were observed in MEP or H-reflex between sessions. Nevertheless, Δ MEP at 40 ms demonstrated a positive correlation with Δ COP, while Δ H-reflex at 40 ms demonstrated a negative correlation with Δ COP. Balance perturbation training led to less body sway and a potential increase in spinal-level involvement, indicating that movement automaticity may be suggested after perturbation training.peerReviewe

Effects of military basic training on VO2max, body composition, muscle strength and neural responses in conscripts of different aerobic condition

Study aim: The purpose of this study was to evaluate neuromuscular adaptations in conscripts with different fitness levels (VO2max) during 8 weeks of military basic training (BT)

Effects of military basic training on VO2max, body composition, muscle strength and neural responses in conscripts of different aerobic condition

Study aim: The purpose of this study was to evaluate neuromuscular adaptations in conscripts with different fitness levels (VO2max) during 8 weeks of military basic training (BT). Material and methods: Twenty-four male conscripts (18–21 years) were divided into two groups (Good Fitness [GF] and Low fitness [LF]) based on their VO2max at the beginning of BT. Body mass (BM), fat free mass (FFM) and Fat% were measured after 2, 4, and 7 weeks of training. VO2max, maximal isometric leg press force (MVC), H-reflex (Hmax/Mmax) at rest and V-wave (V/Mmax) during maximal isometric plantarflexion were measured from the soleus muscle at the beginning, after 5, and after 8 weeks of training. Results: FFM decreased significantly in LF after 7 weeks of training (–3.0 ± 1.7%, p < 0.001), which was not observed in GF. Both GF (6.9 ± 4.6%, p < 0.01) and LF (5.7 ± 4.6%, p < 0.01) showed improved VO2max after 5 weeks, with no changes during the last 3 weeks. A main effect of training was observed in decreased leg press MVC (–7.3 ± 9.3%, F = 4.899, p < 0.05), with no between-group differences. V-wave was significantly lower in LF during 5 (–37.9%, p < 0.05) and 8 (–44.9%, p < 0.05) weeks. Conclusion: Poor development of the neuromuscular system during BT suggests that explosive and/or maximal strength training should be added to the BT protocol for all conscripts regardless of fitness level. In addition, individualized training periodization should be considered to optimize the training load.peerReviewe

Reliability of transcranial magnetic stimulation and H-reflex measurement during balance perturbation tasks

Following ankle movement, posterior balance perturbation evokes short- (SLR ∼30–50 ms), medium- (MLR ∼50–60 ms), and long-latency responses (LLR ∼70–90 ms) in soleus muscle before voluntary muscle contraction. Transcranial magnetic stimulation (TMS) and Hoffmann-reflex (H-reflex) measurements can provide insight into the contributions of corticospinal and spinal mechanisms to each response. Motor evoked potential (MEP) and H-reflex responses have shown good reliability in some dynamic muscle contraction tasks. However, it is still unclear how reliable these methods are in dynamic balance perturbation and corticospinal modulation during long amplitude balance perturbation tasks. 14 subjects completed two test sessions in this study to evaluate the reliability of MEPs, H-reflex, and corticospinal modulation during balance perturbation. In each session, the balance perturbation system operated at 0.25 m/s, accelerating at 2.5 m/s2 over 0.3 m displacement. MEPs and H-reflexes were elicited in the right leg soleus muscle at four delays after ankle movement (10 ms, 40 ms, 80 ms, and 140 ms), respectively. Test-retest reliability of MEP and H-reflex amplitudes were assessed via intraclass correlation coefficients (ICC) both between- and within-session. Between-session test-retest reliability for MEPs was excellent (ICC = 0.928–0.947), while H-reflex demonstrated moderate-to-good reliability (ICC = 0.626–0.887). Within-session reliability for both MEPs and H-reflex was excellent (ICC = 0.927–0.983). TMS and H-reflex measurements were reliable at different delays after perturbation between- and within-sessions, which indicated that these methods can be used to measure corticospinal excitability during balance perturbation.peerReviewe

Older Age Increases the Amplitude of Muscle Stretch-Induced Cortical Beta-Band Suppression But Does not Affect Rebound Strength

Healthy aging is associated with deterioration of the sensorimotor system, which impairs balance and somatosensation. However, the exact age-related changes in the cortical processing of sensorimotor integration are unclear. This study investigated primary sensorimotor cortex (SM1) oscillations in the 15–30 Hz beta band at rest and following (involuntary) rapid stretches to the triceps surae muscles (i.e., proprioceptive stimulation) of young and older adults. A custom-built, magnetoencephalography (MEG)-compatible device was used to deliver rapid (190°·s−1) ankle rotations as subjects sat passively in a magnetically-shielded room while MEG recorded their cortical signals. Eleven young (age 25 ± 3 years) and 12 older (age 70 ± 3 years) adults matched for physical activity level demonstrated clear 15–30 Hz beta band suppression and rebound in response to the stretches. A sub-sample (10 young and nine older) were tested for dynamic balance control on a sliding platform. Older adults had greater cortical beta power pre-stretch (e.g., right leg: 4.0 ± 1.6 fT vs. 5.6 ± 1.7 fT, P = 0.044) and, subsequently, greater normalized movement-related cortical beta suppression post-proprioceptive stimulation (e.g., right leg: −5.8 ± 1.3 vs. −7.6 ± 1.7, P = 0.01) than young adults. Furthermore, poorer balance was associated with stronger cortical beta suppression following proprioceptive stimulation (r = −0.478, P = 0.038, n = 19). These results provide further support that cortical processing of proprioception is hindered in older adults, potentially (adversely) influencing sensorimotor integration. This was demonstrated by the impairment of prompt motor action control, i.e., regaining perturbed balance. Finally, SM1 cortex beta suppression to a proprioceptive stimulus seems to indicate poorer sensorimotor functioning in older adults.peerReviewe