Transcranial Direct Current Stimulation of Primary Motor Cortex over Multiple Days Improves Motor Learning of a Complex Overhand Throwing Task.

Transcranial direct current stimulation (tDCS) applied to the primary motor cortex (M1) improves motor learning in relatively simple motor tasks performed with the hand and arm. However, it is unknown if tDCS can improve motor learning in complex motor tasks involving whole-body coordination with significant endpoint accuracy requirements. The primary purpose was to determine the influence of tDCS on motor learning over multiple days in a complex over-hand throwing task. This study utilized a double-blind, randomized, SHAM-controlled, between-subjects experimental design. Forty-six young adults were allocated to either a tDCS group or a SHAM group and completed three experimental sessions on three consecutive days at the same time of day. Each experimental session was identical and consisted of overhand throwing trials to a target in a pre-test block, five practice blocks performed simultaneously with 20 min of tDCS, and a post-test block. Overhand throwing performance was quantified as the endpoint error. Transcranial magnetic stimulation was used to obtain motor-evoked potentials (MEPs) from the first dorsal interosseus muscle to quantify changes in M1 excitability due to tDCS. Endpoint error significantly decreased over the three days of practice in the tDCS group but not in the SHAM group. MEP amplitude significantly increased in the tDCS group, but the MEP increases were not associated with increases in motor learning. These findings indicate that tDCS applied over multiple days can improve motor learning in a complex motor tasks in healthy young adults.

An acute application of transcranial random noise stimulation does not enhance motor skill acquisition or retention in a golf putting task.

Transcranial random noise stimulation (tRNS) is a brain stimulation technique that has been shown to increase motor performance in simple motor tasks. The purpose was to determine the influence of tRNS on motor skill acquisition and retention in a complex golf putting task. Thirty-four young adults were randomly assigned to a tRNS group or a SHAM stimulation group. Each subject completed a practice session followed by a retention session. In the practice session, subjects performed golf putting trials in a baseline test block, four practice blocks, and a post test block. Twenty-four hours later subjects completed the retention test block. The golf putting task involved performing putts to a small target located 3 m away. tRNS or SHAM was applied during the practice blocks concurrently with the golf putting task. tRNS was applied over the first dorsal interosseus muscle representation area of the motor cortex for 20 min at a current strength of 2 mA. Endpoint error and endpoint variance were reduced across the both the practice blocks and the test blocks, but these reductions were not different between groups. These findings suggest that an acute application of tRNS failed to enhance skill acquisition or retention in a golf putting task.

Cerebellar Transcranial Direct Current Stimulation Enhances Motor Learning in a Complex Overhand Throwing Task.

Cerebellar transcranial direct current stimulation (c-tDCS) enhances motor adaptation, skill acquisition, and learning in relatively simple motor tasks. The purpose was to examine the influence of c-tDCS on motor learning in a complex overhand throwing task. Forty-two young adults were randomized to a c-tDCS group or a SHAM group and completed a practice session and a retention session. The practice session involved an overhand throwing task to a small target (6 m away) in a pre-test block, 6 practice blocks, a post-test block, and a retention-test block (24 h later). c-tDCS or SHAM was applied during overhand throwing in the practice blocks. The decline in endpoint error was greater for the tDCS group compared to SHAM at the end of practice (P = 0.019) and at retention (P = 0.003). The findings indicate that a single application of c-tDCS enhances motor learning in a complex overhand throwing task.

Acute effects of static and ballistic stretching on measures of strength and power.

Preactivity stretching is commonly performed by athletes as part of their warm-up routine. However, the most recent literature questions the effectiveness of preactivity stretching. One limitation of this research is that the stretching duration is not realistic for most athletes. Therefore, the purpose of this study was to determine the effects of a practical duration of acute static and ballistic stretching on vertical jump (VJ), lower-extremity power, and quadriceps and hamstring torque. Twenty-four subjects performed a 5-minute warm-up followed by each of the following three conditions on separate days with order counterbalanced: static stretching, ballistic stretching, or no-stretch control condition. Vertical jump was determined with the Vertec VJ system and was also calculated from the ground-reaction forces collected from a Kistler force plate, which also were used to calculate power. Torque output of the quadriceps and hamstrings was measured through knee extension and flexion on the Biodex System 3 Dynamometer at 60 degrees x s(-1). Data normalized for body weight were analyzed using five separate, 3 (stretch condition) x 2 (gender) analysis-of-variance procedures with repeated measures on the factor of stretch condition. The gender x stretch interaction was not significant for any of the four measures, suggesting that the stretching conditions did not affect men and women differently. The results of this study reveal that static and ballistic stretching did not affect VJ, or torque output for the quadriceps and hamstrings. Despite no adverse effect on VJ, stretching did cause a decrease in lower-extremity power, which was surprising. Because of the mixed results, strength coaches would be better served to use dynamic stretching before activity; this has been consistently supported by the literature.

Effect of hamstring-emphasized resistance training on hamstring:quadriceps strength ratios.

A decreased hamstring:quadriceps (H:Q) ratio may put the hamstrings and anterior cruciate ligament (ACL) at increased risk of injury. Therefore, the purpose of this study was to evaluate H:Q ratios of 12 female National Collegiate Athletic Association soccer players, and to test the effects of a 6-week strength training program on these ratios. Each subject completed 2 practice sessions before a pretest. Subjects then completed 6 weeks of strength training that included the addition of 2 hamstring specific exercises, followed by a posttest. Peak torque during concentric and eccentric actions for both hamstrings and quadriceps was measured with an isokinetic dynamometer. Each muscle action was tested at 3 angular velocities in the following order: concentric 240, 180, and 60 degrees x s(-1) and eccentric 60, 180, and 240 degrees x s(-1). The H:Q strength ratio was evaluated using concentric muscle actions (concentric hamstrings:concentric quadriceps). This method is commonly used and is thus called the conventional ratio. Because concentric actions do not occur simultaneously in opposing muscles, a more functional assessment compares eccentric hamstring actions to concentric quadriceps actions. This functional ratio was also analyzed. Mean conventional and functional H:Q ratio data were analyzed using separate analysis of variance procedures with repeated measures on all factors (2 [Test] x 2 [Leg] x 3 [Angular Velocity]). The results revealed a significant main effect for factor (F test) with the functional ratio (p < 0.05) but not for the conventional ratio. The mean functional ratio increased from 0.96 +/- 0.09 in pretest to 1.08 +/- 0.11 in posttest. These results suggest that 6 weeks of strength training that emphasizes hamstrings is sufficient to significantly increase the functional ratio. The functional ratio after training exceeded 1.0, which is specifically recommended for prevention of ACL injuries.

The acute effects of mechanical vibration on power output in the bench press.

This study was designed to investigate the effect of mechanical vibration on acute power output in the bench press exercise. Ten male subjects who were experienced in resistance training participated in this study. Each subject performed 3 sets of 3 repetitions in the bench press exercise using a load equal to 70% of 1 repetition maximum in each of 2 sessions separated by 3 days. One session served as the experimental (vibration) condition, whereas the other session served as the control (no vibration) condition. The intervention (vibration or control) was applied between sets 2 and 3. The vibration was applied by a vibrating barbell apparatus held by the subjects while lying supine on a bench. The only difference between the 2 conditions was the vibration of the barbell apparatus during the vibration condition. Peak and average power were calculated during each bench press set to determine whether power output differed following vibration compared to control. Average power was significantly higher for the vibration condition compared to the control (525 +/- 74 vs. 499 +/- 71 W; p = 0.01). There was also a trend toward an increase in peak power in the vibration condition (846 +/- 168 by vs. 799 +/- 149 W; p = 0.06). In general, peak and average power output were higher following the vibration intervention compared to control. However, the sets prior to vibration application during the vibration condition also demonstrated higher power outputs compared with the control condition, which contributed to the main effect for the vibration condition. These results suggest that factors other than the vibration intervention influenced task performance during the vibration condition. We suggest that psychological factors related to the novelty of the vibration intervention were involved. These factors may partially explain the conflicting results of previous investigations that examined vibration as an exercise intervention.

Reciprocal influences of attentional focus on postural and suprapostural task performance.

The authors examined the influence that attentional focus on either a postural or a suprapostural task had on the performance of each task. Participants (N = 32) stood on an inflated rubber disk and held a pole horizontally. All participants performed under 4 attentional focus conditions: external (disk) or internal (feet) focus on the postural task, and external (pole) or internal (hands) focus on the suprapostural task. Compared with internal focuses, external focuses on either task resulted in similar and reduced postural sway. Response frequency on each task increased when participants focused on the respective task. Finally, an external focus on either task produced higher frequencies of responding on the suprapostural task. The authors conclude that suprapostural task goals have a stronger influence on postural control than vice versa, reflecting the propensity of the motor system to optimize control processes on the basis of the desired movement effect.

Challenge point: a framework for conceptualizing the effects of various practice conditions in motor learning.

The authors describe the effects of practice conditions in motor learning (e.g., contextual interference, knowledge of results) within the constraints of 2 experimental variables: skill level and task difficulty. They use a research framework to conceptualize the interaction of those variables on the basis of concepts from information theory and information processing. The fundamental idea is that motor tasks represent different challenges for performers of different abilities. The authors propose that learning is related to the information arising from performance, which should be optimized along functions relating the difficulty of the task to the skill level of the performer. Specific testable hypotheses arising from the framework are also described.

The relationship between knowledge of results and motor learning in Parkinsonian patients.

A simple timing movement was used to investigate augmented feedback on motor learning in Parkinson's disease (PD) patients and controls. During acquisition, participants received knowledge of results (KR) about their errors after every trial (100%) or every fifth trial (20%). Participants then performed a retention test without KR. Controls performed better on the retention test after having had 20% KR during acquisition. PDs showed superior retention with 100% KR. This suggests that the PD patients are more reliant on KR for learning motor skills; a difference that may be attributable to reduced proprioceptive acuity in PD patients.