Ben Sidaway

Acute effects of stretching on the neuromechanical properties of the triceps surae muscle complex.

Abstract. Previous research has shown that an acute bout of passive muscle stretching can diminish performance in certain movements where success is a function of maximal force and/or power output. Two possible mechanisms that might account for such findings are a change in active musculotendinous stiffness and a depression of muscle activation. To investigate the likelihood of these two mechanisms contributing to a post-stretch reduction in performance, we examined the acute effects of stretching on the active stiffness and muscle activation of the triceps surae muscle group during maximal single-joint jumps with movement restricted to the ankle joint. Ten males performed both static (SJ) and countermovement (CMJ) jumps before and after passively stretching the triceps surae. Electrical activity of the triceps surae during each jump was determined by integrating electromyographic recordings (IEMG) over the course of the movement. Triceps surae musculotendinous stiffness was calculated before and after stretching using a technique developed by Cavagna (1970). Following stretching, a significant decrease [mean (SD) 7.4 (1.9)%; P<0.05] in jump height for the CMJ occurred, but for the SJ, no significant (P>0.05) change in jump height was found. A small but significant decrease [2.8 (1.24)%; P<0.05] in stiffness was noted, but the magnitude of this change was probably not sufficient for it to have been a major factor underlying the decline in CMJ performance. Paradoxically, after stretching, the SJ exhibited a significant (P<0.05) decrease in IEMG, but the IEMG for the CMJ remained unchanged (P>0.05). It appears that an acute bout of stretching can impact negatively upon the performance of a single-joint CMJ, but it is unlikely that the mechanism responsible is a depression of muscle activation or a change in musculotendinous stiffness.

Kicking performance in relation to balance ability over the support leg

Balance control is presumed to be a fundamental constraint on the organization of skilled movement. The current experiment explored whether single-leg balance ability predicted kicking performance on the other leg. Thirty-eight participants ranging widely in skill kicked a soccer ball with the right and left legs for maximum accuracy and velocity and performed single-leg balance on a force plate for 30 s with the right and left legs. Significant correlations between single-leg balance and kicking accuracy, but not velocity, were found. Left leg balance was more highly correlated than right leg balance with right (dominant) leg kicking accuracy. However, the same pattern of relations was not seen between single-leg balance and left (non-dominant) leg kicking accuracy. These findings provide preliminary support for the importance of balance ability in kicking performance. The importance of balance in the production of athletic skills is discussed and additional experimental paradigms are suggested that might further our knowledge in this area.

A comparison of manual guidance and knowledge of results in the learning of a weight-bearing skill.

Background and Purpose: Patients with certain neurological or orthopedic conditions often present with asymmetrical weight-bearing in stance. In the treatment of such patients, physical therapists often use manual guidance to promote symmetrical weight-bearing. Research investigating the efficacy of manual guidance to effect a change in weight-bearing status however, is lacking. As a first step in assessing the utility of such guidance, the present study compared the effect of providing two frequencies of manual guidance and of knowledge of results (KR) in the learning of a weight-bearing skill in healthy subjects. Subjects and Methods: Forty healthy subjects (20 males and 20 females) with a mean age of 21.8 years (SD = 4.9 years) were randomly assigned to one of four groups differentiated on the basis of the type and frequency of information provided for learning. Subjects were required to learn to distribute their weight on their feet at a 70:30 ratio. Following a pretest, one group of subjects was positioned by experimenter-provided manual guidance at the hips until 70% of their weight was on one foot, as determined by a bathroom scale. This guidance was provided on every trial for 10 blocks of 12 trials (GD100%). A second group was provided with guidance on every third trial (GD33%), with the other two trials being performed without any assistance. A third group was verbally provided with KR regarding the percentage of body weight on the test foot after every trial (KR100%) while the final group was given KR after every third trial (KR33%). Following acquisition, retention tests were performed 10 minutes, one day, and one week later during which no feedback or guidance was given. Results: No difference between groups was found at the pretest, but an analysis of variance performed on the accuracy of achieving the 70% goal in retention revealed main effects for technique and frequency. These effects were overshadowed by a significant interaction of these variables with retention test. Analysis of this interaction revealed that the most accurate performance was exhibited by the KR33% group while the GD100% group consistently exhibited the poorest learning. The GD33% and KR100% groups showed a decrease in performance accuracy with time following practice. Discussion and Conclusion: These results indicate that infrequent KR was the most effective technique in learning to modify weight-bearing status and that frequent manual guidance during practice is ineffective for learning this task. The next step is to determine whether these findings hold in subjects with various orthopedic and neurological conditions.

Interaction of Feedback Frequency and Task Difficulty in Children's Motor Skill Learning

Background Providing adults with knowledge of results (KR) after each practice trial (100% KR) usually is found to be detrimental to motor skill learning compared with conditions in which feedback is less frequently provided. The effect of 100% KR on childrens learning is less clear, with research showing that children with cerebral palsy benefit from less frequent KR, whereas children with typical development do not. Objective This study was designed to examine the interaction of KR frequency and task complexity on the acquisition, retention, and transfer of a novel throwing skill in fourth- and fifth-grade children with typical development. Design This was an observational study. Methods Children threw beanbags for accuracy at an unseen target while walking or while standing still. These 2 levels of task complexity were crossed with 2 frequencies (33% and 100%) of KR provision. Following practice, retention tests without feedback were performed 5 minutes later and then 1 week later along with transfer tests to assess the generalizability of learning. Results Analyses revealed that learning was improved on the easy version of the task when a 33% KR frequency was provided during practice. In contrast, in the difficult version, learning was facilitated by provision of a 100% KR frequency during practice. Conclusions Structuring practice conditions for children should take into account task complexity and feedback frequency in determining the cognitive challenge necessary for optimal skill learning. More generally, the findings suggest that practitioners teaching motor skills should design practice conditions in accordance with the cognitive processing capacity of the learner.

Comparing the reliability of a trigonometric technique to goniometry and inclinometry in measuring ankle dorsiflexion

OBJECTIVES The purpose of this study was to compare the reliability of three previously used techniques for the measurement of ankle dorsiflexion ROM, open-chained goniometry, closed-chained goniometry, and inclinometry, to a novel trigonometric technique. METHODS Twenty-one physiotherapy students used four techniques (open-chained goniometry, closed-chained goniometry, inclinometry, and trigonometry) to assess dorsiflexion range of motion in 24 healthy volunteers. All student raters underwent training to establish competence in the four techniques. Raters then measured dorsiflexion with a randomly assigned measuring technique four times over two sessions, one week apart. Data were analyzed using a technique by session analysis of variance, technique measurement variability being the primary index of reliability. Comparisons were also made between the measurements derived from the four techniques and those obtained from a computerized video analysis system. RESULTS Analysis of the rater measurement variability around the technique means revealed significant differences between techniques with the least variation being found in the trigonometric technique. Significant differences were also found between the technique means but no differences between sessions were evident. The trigonometric technique produced mean ROMs closest in value to those derived from computer analysis. CONCLUSIONS Application of the trigonometric technique resulted in the least variability in measurement across raters and consequently should be considered for use when changes in dorsiflexion ROM need to be reliably assessed.

Contextual Interference Can Facilitate Motor Learning in Older Adults and in Individuals With Parkinson's Disease

ABSTRACT In healthy young adults motor learning is typically improved by practice under conditions of high contextual interference such as that created when a series of skills are practiced in a random sequence. The authors examined whether individuals with Parkinsons disease and age-matched older adults might also benefit from such a learning environment. Participants learned 3 peg placement movements under both random practice and blocked practice schedules. Participants completed free-recall, cued-recall, and transfer tests 1 day and 1 week following practice. During acquisition all learners had shorter movement times (MTs) during blocked than random practice but during retention testing, MTs were shorter if the patterns had been learned with random practice. Fewer errors during free recall following random practice were evident in both groups of learners and MTs to complete a novel transfer task were shorter following random practice. These findings suggest employing a cognitively challenging practice environment might improve motor skill learning in elderly learners and in people with Parkinsons disease.

The effect of cane length on the haptic perception of height

Purpose: The purpose of this investigation was to determine whether the ability to haptically perceive object height is a function of the length of cane being wielded by blindfolded individuals. Method: Fifteen sighted females between the ages of 18 and 25 years volunteered to participate in the study. Five different heights of wooden blocks were haptically explored with four different cane lengths (0.92, 1.22, 1.37 and 1.67 m), cane length order being randomized across 2 days of testing. Subjects were asked to report whether the explored blocks height was taller, shorter, or equal to that of a previously presented standard block. The percentages of correct judgments for each cane and block height combination were subjected to statistical analysis. Results: The analysis revealed significant main effects for cane length, F (3, 42) = 9.47, p < 0.0001, and block height, F (4, 56) = 17.69, p < 0.0001. The interaction of cane length and block height was not significant, F < 1. The accuracy of haptic perception improved with decreased cane length and increased difference in height from the standard block. Conclusion: Contrary to previous research on haptic perception in which probe length was found not to affect judgment accuracy, the present study found a marked influence of cane length on perceptual accuracy. This finding indicates that length is an important property that should be taken into account when prescribing canes for the visually impaired.

The Role of Postural Support in Young Adults’ Control of Stationary Kicking

ABSTRACT Purpose: The requirement for postural stability during the performance of motor skills has been clearly demonstrated in infants, but the necessity for such a postural substrate is not well documented in adults. The present study investigated the role of postural stability during a ballistic ball-kicking task in adults by providing varying degrees of external postural support. Method: In the 1st experiment, 30 participants performed 20 maximal-velocity kicks under each of 3 conditions: grasping a rigid stable handle, light fingertip touch, and grasping a suspended elastic tube. A 2nd experiment with 16 participants varied the position of the stable handle to examine if the handle position in Experiment 1 might simply act as a fulcrum to enhance torque generation. Results: In Experiment 1, ball velocity was significantly higher in the stable-grasp condition in both men and women with the men showing greater improvement relative to the other conditions. Experiment 2 showed that the position of the stable handle did not significantly affect kicking velocity, indicating that the handle was not simply acting as a fulcrum during the kick. Conclusion: Together, the findings suggest that postural stability may be a rate limiter in the performance of dynamic motor tasks in adults.

The role of head position and prior contraction in manual aiming

We sought to determine if the asymmetrical tonic neck reflex influences the accuracy of self-selected arm positioning without vision and to ascertain if such accuracy is influenced by a pre-contraction of the prime movers. Participants reproduced an arm position using their abductors with the head in midline, rotated towards and away from the arm. Arm movements were made with and without a pre-contraction of the abductors. Twenty participants performed eight trials in each of the six different conditions. Compared to the midline position, participants undershot the reference position with the head turned away and overshot the position with the head rotated towards the arm. A pre-contraction caused undershooting regardless of head position. Results suggest that head position and pre-contraction may have significant and independent effects on arm positioning.