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Research Day 2008
2008 Research Day Schedule (pdf)
Brad Millington - New Technologies, the Sporting Body, and Government(ality)
In this presentation I discuss some of my research on technologies that are (re)shaping experiences and perceptions of physical activity. My focus in this analysis is twofold. I am first concerned with the ways that new devices intervene in exercise contexts by forming human/non-human conventions, or hybrids. Bruno Latour contends that insufficient attention has been paid to the manner in which objects and subjects – both of which have the potential to act with agency – are brought together through processes he calls ‘translation’. Human agency, Latour argues, is invested in objects during production, while non-humans are equally ‘folded in’ to humans in their connections to the body. I use Nintendo’s new product ‘the Wii’ as a specific example of a technology that renders intricate ties between people and machines. My second area of focus builds from this discussion of hybridity. I will contend that, once connected to the human body, technologies such as the Wii have the potential to act as tools that assist in the governing of individuals and populations. This analysis is informed by Foucault’s work on governmentality, where government is understood as the conduct of conduct, and power is described as flowing through both downwards and upwards continuities. In addition, I draw from post-Foucauldian scholars who have identified the salience of ‘risk’ communities to contemporary forms of government. I conclude this discussion by summarizing some of the possible benefits of new sporting technologies, while highlighting how they may be problematic as well.
Megan MacGillivray - Reflex Modulation and Neuromuscular Characteristics During Wheelchair Locomotion
The aim of this study will be to compare reflex modulation and neuromuscular characteristics between adult-onset, child-onset and naïve manual wheelchair users during wheeling locomotion. 15 subjects will be recruited from each of the three groups of interest. EMG will be collected for several upper extremity superficial muscles. These will include the prime movers and prime recovery muscles used during manual wheelchair locomotion. Cutaneous reflexes will be evoked throughout the wheeling cycle with trains of constant current electrical stimulation which will be applied pseudorandomly. EMG data will be analyzed for reflex amplitudes and latencies following electrical stimulation. Percent cycle activation and percent cycle duration for each muscle will also be analyzed to provide further insight into the wheeling strategy. It is hypothesized that child-onset manual wheelchair users develop different wheeling strategies as a result of an adaptation of the central pattern generator when applied to the arms as the sole source of locomotion. These variations in wheeling strategies could be responsible for the low incidence of pain and shoulder injuries observed in this group.
Christopher Edwards, Shaun Luttin, Alison Bowcock and Nicola J. Hodges - Learning from the experts: Gaining insights into best practice during the acquisition of three novel motor skills
The amount and quality of practice predict expertise. However, optimal conditions of practice have only been explored with novice learners. We examined how expert musicians structure practice of a novel skill. Are experts, expert at practicing? Ten expert musicians and ten non-motor experts practiced three skills (Frisbee throws) during a one-hour practice session for evaluation 24 hours later. The skills varied in difficulty. Participants self-scheduled their practice and could request augmented information. The groups did not differ in terms of the type of practice schedule and overall error. Three experts and five novices adopted a blocked schedule (switched skills less than ten times; experts, M = 14.4; novices, M = 17.4 switches). For the experts, random practice was associated with greater improvements pre to post practice (r = .26, between the number of switches and improvement in accuracy). The reverse was true for the novice group (r = -.33). This finding was independent of the number of throws. Requests for augmented information were similar across groups (experts, M = 12; novices, M = 8). However, the experts showed more agreement as to when they thought information should be provided and their practice concurred with their beliefs (both before and during practice). Both groups reported that they would spend more time practicing the more difficult skill in the questionnaire. This was supported during practice (experts = 39 %; novices = 47 %). The novices also spent more time practicing the easiest skill (31 %) in comparison to the experts (26 %). Although the groups did not differ in terms of the method of practice, the best type of practice interacted with skill level. Only the experts benefited from a more random schedule suggesting that the benefits of this schedule are dependent on past practice experiences. Further testing is underway.
Doug Brairer - Home advantage: The same athletes. The same rules. Different result?
Despite comprehensive, wide ranging research on home advantage, few practical interventions have emerged for coaches and sport psychology practitioners to work with. While the existence of home advantage is not in question, predicting it's scale and source in any given situation is still an inexact science. There are large variations in scale between sports and even within sports, and the empirical evidence behind its predictive factors remains equivocal. So, what can a coach or sport psychology practitioner do to help a team/athlete to enhance their own home advantage or reduce their opposition’s? This study proposes a framework to identify the scale of his team/athlete’s home advantage and the likely predictive factors behind it. It then applies an interactionist (sport:team:athlete), goal setting based approach, to suggest how a coach or sport psychology practitioner may intervene to enhance or neutralise home advantage.
Morton, K. L., & Beauchamp, M. R. - Transformational teaching and physical activity among adolescents: What is it and does it matter?
A potentially important framework, and one that has yet to be applied to the fields of health promotion, behavioral medicine, and indeed physical education, relates to the full range model of leadership developed by Bass and colleagues (Bass & Riggio, 2006). This model conceptualizes transformational and transactional leadership. The purposes of this study were twofold. Using a qualitative interview-based methodology, the first purpose of this study was to examine the extent to which transformational behaviors manifest themselves within school-based physical education settings. The second purpose was to examine the extent to which transformational teaching behaviors, as utilized by physical education teachers, were aligned with adaptive physical activity outcomes among adolescents. Semi-structured interviews were conducted with 18 students (10 females, 8 males, M age = 14 years) and data were analyzed using a constructivist grounded theory approach (Strauss & Corbin, 1990). Results revealed that students who perceived their physical education teachers to utilize transformational behaviors (e.g., idealized influence) also described more adaptive responses, which were categorized as cognitive (e.g., self-efficacy to be physically active), affective (e.g., satisfaction with the teacher) or behavioral (e.g., effort in class) in nature. Directions for future research and theory development are addressed, along with implications that relate to the fostering of physically active lifestyles among children and adolescents.
Jordan Guenette - Novel techniques to assess blood flow regulation in humans.
The purpose of this presentation is to highlight some recent work that I conducted at the Copenhagen Muscle Research Centre (CMRC) in Denmark. The CMRC has established itself as a world leader in exercise and cardiovascular physiology and they are currently using some unique and advanced techniques to understand blood flow regulation in humans. In this talk I will discuss methods such as the Near Infrared Spectroscopy and Indocyanine Green Dye (NIRS-ICG) technique to measure muscle blood flow, laser Doppler to measure adipose tissue blood flow and microdialysis to measure muscle interstitial vasodilator compounds. I will also highlight how we can understand blood flow regulation by infusing specific vasodilators and blockers into an exercising limb. I will then briefly discuss a recent study that I completed at the Department of Critical Care Medicine and Pulmonary Services at the University of Athens in collaboration with researchers from Denmark, Canada and the USA. We became the first group of researchers to successfully quantify blood flow to the respiratory muscles in conscious humans. This study may lead to future investigations aimed at understanding respiratory muscle blood flow regulation during exercise and may also be used to further understand the pathophysiology of debilitating conditions such as chronic obstructive pulmonary disease and chronic heart failure.
Pei Wang - A study on the association between the seven informative variants in the nitric oxide synthase 3 (NOS) gene and acute mountain sickness (AMS) susceptibility in Nepalese.
Nitric oxide (NO), a powerful vasodilator, is involved in a variety of physiological functions including maintaining pulmonary vascular tone and may play a role in altitude adaptation. Nitric oxide synthase 3 (NOS3) is a member of nitric oxide synthase family and synthesized NO from L-arginine. A number of the polymorphisms in the NOS3 gene are associated with NO levels and with cardiovascular dysfunction. In this study, we applied a genetic analysis named as haplotype analysis to investigate the association between the NOS3 gene variants and acute mountain sickness. We used HapMap (http://www.hapmap.org/whatishapmap.html) which is the database of an international project and contains the latest haplotype data of human genome. Seven tag-variants in the gene that encodes the eNOS were chosen from HapMap. We genotyped these variants in a cohort of individuals with, or without, AMS who were ascertained at the Janai Purnima Festival at Lake Gosain Kunda, Nepal (4380 meters). The data collection and the statistical analysis would be finished before the HKIN Research Day. This study represents the application of the powerful HapMap database to understanding the association between eNOS gene and AMS susceptibility. |
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Scott Apperley - DIFFERENTIAL FUNCTIONING OF DEEP AND SUPERFICIAL LUMBAR MULTIFIDUS FIBRES DURING VERTEBRAL INDENTER PERTURBATIONS
Lumbar multifidus has been implicated as having a specialized role in lumbar spine stability. Recent literature has suggested that the deep and superficial fibres of lumbar multifidus function differentially during spinal stability tasks. Deep fibres appear to stabilize the lumbar spine while superficial fibres function primarily as global movers of the trunk. These findings have been used clinically in low back pain rehabilitation programs and have been incorporated into lumbar spine stabilization techniques. To investigate lumbar multifidus differential functioning, intramuscular electromyography (EMG) was recorded from lumbar multifidus at three vertebral levels (L3, L4 and L5). A motor was used to apply spinal indentation forces of varying velocity (10, 150, 400mm/s) and displacement (5, 6.25, 7.5mm) to the spinous process of these vertebrae. Perturbations consisted of a rapid indentation followed by a 500ms hold at a specific displacement and a rapid return to starting position. It was hypothesized that deep and superficial lumbar multifidus fibres would respond differentially such that increased perturbation depth and velocity would cause greater increases in the superficial fibre response. Integrated EMG during the rapid indentation and hold phase of each perturbation was computed and compared across perturbation levels, velocities and displacements. Greater EMG responses were noted with larger perturbation velocities and displacements. The different EMG responses with perturbation magnitude could be used clinically to inform low back rehabilitation programs.
Davis, J.R., Fukushima, K., Chua, R. & Carpenter, M.G. - Elevated postural threat does not increase the gain of sensory afferent information.
Characteristic changes in postural control occur when standing at extreme surface heights. This study investigated whether or not the perception of proprioceptive information would be facilitated concomitantly to changes in postural control under conditions of elevated postural threat. 21 healthy young participants stood quietly at ground level and at the edge of a 3.2m platform while receiving trains of electrical stimulation to the tibial nerve. The peak to peak amplitude of the sensory evoked potential (SEP) recorded using electroencephalography (EEG) from the Cz position 30-40ms after stimulation onset was compared between heights as well as changes in centre of pressure (COP) parameters and electrodermal activity (EDA). When standing at 3.2m, the mean peak to peak amplitude of the recorded SEP 30-40ms after stimulation onset was found not to increase compared to when standing on the ground. The mean position of COP was observed to be 32.4% further from the edge of the elevated platform, mean power frequency of COP increased by 18.1% and root mean square of COP decreased by 62.9% at 3.2m compared to when standing on the ground. This evidence suggests that the changes in posture and EDA observed under conditions of increased postural threat are not facilitated by changes in how somatosensory information is relayed to the cortex.
Sherry Hunt - Advanced Breast Cancer Exercise Intervention: A Single Armed Phase II Clinical Trial
Physical exercise may be an inexpensive non-medicinal treatment for advanced breast cancer (ABC) patients. The effect of exercise on ABC disease activity has not been examined. Exercise has not been used in ABC patients to explore the links between metabolic and cancer molecular pathways. The purpose of the ABC Exercise Intervention is to examine how a progressive physical activity program, involving aerobic and resistance exercises, affects the physical fitness, body composition, quality of life (QoL), and levels of cancer biomarkers (CA 15-3, CA-125 and CEA) and metabolic substances (insulin, insulin-like growth factors, leptin and adiponectin) in the blood of women with metastatic breast cancer. The intervention involves 2 weekly sessions for 3 months. Aerobic intensity on the bike, treadmill or elliptical machine starts at 10 beats per minute below the heart rate at the ventilatory threshold (baseline measurement), and increases depending on subject performance. Aerobic training duration depends on baseline fitness levels, and increases up to 30 minutes. For muscular strength and endurance, 2 sets of 10 resistance exercises using all major muscle groups will be performed at 8 to 12 repetitions. Exercises will be increased in weight when 13 repetitions can be performed. Pre and post-intervention tests will include FACT-B quality of life questionnaires, DXA body composition assessments, graded treadmill VO2 maximum tests, estimated one repetition maximum tests (ERM 1) for bench press and leg press, maximum repetition tests with ½ the weight of baseline ERM 1, sit and reach tests, and blood tests (ELISA).
Chris Dakin - Narrow Bandwidth Vestibular Stimulation
The vestibular system contributes to postural control though determination of head acceleration. To probe the vestibular system researchers use techniques such as stochastic vestibular stimulation; the process of applying a small electric current bilaterally to the mastoid processes. The applied electric current modulates the firing rate of underlying vestibular nerve afferents, resulting in a biphasic electromyographic (EMG) response in posturally active muscles. Recently, we characterized vestibular evoked EMG responses with a broad bandwidth stimulus (0-50Hz). Broad bandwidth stimuli allowed analysis of vestibular responses in the frequency domain providing additional information on the frequency composition of the biphasic muscle response. Through a frequency based correlation known as coherence, we found vestibular evoked EMG responses to be composed of signals in two frequency bandwidths, a late 2-10Hz component and an earlier 11-20Hz component. We hypothesized that by stimulating with narrow bandwidth stimuli, the early (11-20Hz) or late components (2-10Hz) of the biphasic muscle response may be isolated. Ten subjects participated in eight stochastic stimulus conditions consisting of seven narrow bandwidth stimuli (0-5, 5-10, 10-15, 15-20, 20-25, 25-30, 30-35Hz) and one broad bandwidth stimuli (0-35Hz). Individual narrow bandwidths of stimulation were not capable of preferentially isolating the early or late component of the biphasic muscle response. However, the early component of the muscle response appears to be composed of a broad bandwidth of frequencies of 5-25Hz and the late component composed of frequencies from 0-20Hz. These results indicate that the net narrow bandwidth responses approximate those of the broad bandwidth stimuli.
Mona Maghsoodi - Genetic Variation as a Tool for Homologous Blood Doping
The aim of this study is to determine the feasibility and efficiency of genetic variation as a potential way to detect homologous blood doping. Homologous blood is the transfusion of whole blood from one individual to another for the purpose of increasing oxygen delivery capacity and thus improving endurance during competition. Currently, flow cytometry has been used in doping control to detect mixed blood cell populations; however, this method is expensive and requires careful sample storage. Genetic variation among individuals allows for the detection of different blood cell populations using DNA based assays. This pilot study did not involve blood transfusion. Blood from two individuals was mixed in a test-tube in the following ratios: 100: 0 (pure) 99: 1, 90: 10 and 50: 50. DNA was extracted from the mixtures and polymerase chain reaction amplification was performed to determine genotypes at a variable genetic site in the ACE gene. The presence of foreign blood can be detected at very low dilutions. Typically, blood doping occurs at a 90:10 ratio (i.e. one unit (500 ml blood added to the athletes circulation (~5 liters). Our results suggest that this technique could be used detect homologous blood doping. Such a test would be easy, inexpensive, and alleviate the problem of maintaining sample quality.
Danny Mang - Directional Dependency of Lumbar and Lower Limb Muscle Responses During Galvanic Vestibular Stimulation Elicited Balance Perturbation
In a 2003 survey of Canadians aged 18 and over, 69% of adults suffered from moderate or severe back pains. Some clinical rehabilitation techniques suggest deep and superficial lumbar multifidus (LM) muscles have different roles in spinal stability. Deep LM fibres have been described to function as spinal stabilizers; whereas, superficial LM fibres function as force generators/prime movers. In this study, we used galvanic vestibular stimulation (GVS) to evoke whole-body balance perturbations and to probe the human vestibular system. The ability to control the direction of the whole-body GVS perturbation allowed us to investigate the response of deep and superficial LM fibres to known perturbation direction. We hypothesize that deep and superficial LM fibres will exhibit different directional dependent functions as a result of whole-body balance perturbations. Six subjects from a university population participated in this study. All subjects had their head oriented in three different directions: head forward, head 90 yaw left and head 90 pitch downwards. Square-wave GVS pulses (2 seconds, 2.5 mA, bipolar, binaural) were used to elicit whole body balance responses. Indwelling electromyography (EMG) electrodes were used to measure superficial and deep LM fibre activity at L3, L4, and L5. Surface EMG electrodes were used to record from bilateral biceps femoris, tibialis anterior, and medial gastrocnemis. Muscle and balance responses were quantified using trigger averages of a 300ms window after the onset and offset of the GVS pulse. In both head forward and head left conditions, superficial and deep LM fibres exhibited direction specific responses. This indicates that deep and superficial LM fibres respond similarly to whole-body balance perturbations and may indicate similarly functionality.
Meaghan MacNutt, Paul Laursen, Shiksha Kedia, Maniraj Neupane, Parash Parajuli, Jhapindra Phokarel and A. William Sheel - Destination Gokyo: acclimatisation, de-acclimatisation and re-acclimatisation in high altitude trekkers
We conducted a field study to determine whether the process of hypoxic acclimatisation is facilitated by a recent sustained exposure to high altitude. Six low altitude natives (4M, 2F; 27 ± 5 years) were monitored throughout two identical treks to high altitude in the Solu Khumbu region of Nepal. Both altitude exposures (initial acclimatisation (IA) and re-acclimatisation (RA)) consisted of the same ten day trek to 5360m separated by a ten day de-acclimatisation period (DA) at 1300m. Acute mountain sickness (AMS) scores, trekking times, perceived trekking intensities and self-treatment with acetazolamide and analgesics were logged daily throughout both treks. Haematology and cardiorespiratory function during rest and exercise were measured before each trek and throughout IA and RA. Trekking time, trekking intensity, AMS scores and acetazolamide consumed were all reduced in RA compared to IA. Blood haemoglobin concentration was elevated throughout RA as compared to IA despite having returned to baseline before beginning the second trek. No differences were seen in cardiorespiratory function at rest or during exercise between IA and RA. We show no evidence for a facilitated cardiorespiratory acclimatisation in RA compared to IA, but the magnitude of the haematological response to altitude was greater in RA. This may not fully explain why trekkers felt better and found the trekking easier the second time. Psychological factors and fitness gains might also contribute to functional improvements seen in RA. Although these findings support anecdotal evidence that recent experience at altitude facilitates subsequent acclimatisation we have little physiological data to support why this is the case. Further mechanistic work is required. Acknowledgements - NSERC, HSFC |
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Dave Nichol - Muscle activation in response to an auditory startle stimulus
An auditory startle reflex is a motor response to an unexpected auditory stimulus. The muscle activation in response to an auditory startle stimulus, can become attenuated or even disappear after repeated exposures to the stimulus. The reflex is proposed to propagate through the reticular formation and then down the reticulospinal tract to the neuromuscular junctions to elicit responses. A new response to repeated auditory stimuli (RAS) has been discovered. This response differs from startle as it is present after repeated exposures to acoustic stimuli. This response to RAS is present in soleus when participants are lying down, tonically activating their soleus muscles and exposed to a 40 ms duration, 124 dB 1000 Hz auditory stimulus repeatedly at intervals of 3-5 seconds. The RAS reflex is a new area of investigation. It is not known if it shares commonalities with the acoustic startle reflex, or if it is a completely separate response by the body. The purpose of this research was to investigate responses to RAS for further understanding of this reflex. Ten volunteers were recruited for the study. Surface EMG data was collected from the muscle bellies of the right OOc, the right and left SCM, the right and left soleus, the right and left deltoid and the right and left medial gastroc muscles. Participants lay on a clinical examination bed with their feet against a stationary platform perpendicular to the bed. During the trials, participants maintained a plantar flexion contraction of both feet. Participants were exposed to a minimum of six single auditory stimuli at 124 dB during experimentation. Participants were then exposed to 210 repeated auditory stimuli at 124dB. Analysis revealed responses noted in the literature as startle responses to the single auditory stimuli. All participants exhibited responses to RAS in the soleus muscles once muscle EMG was root mean squared and trigger-averaged to the onset of the acoustic stimuli. Responses to RAS were present with our without the presence of SCM activation. All participants demonstrated a response with an average of 4 oscillations in their soleus.
Melanie Roskell - Reflexive muscular responses related to vestibular inputs
My current research interests involve the reflexive muscular responses related to vestibular inputs. Traditionally, research in this field has investigated these responses using transient electrical stimulation of the vestibular apparatus, known as galvanic vestibular stimulation or GVS, to provide an erroneous vestibular input to the brain. Recently, pseudo-random GVS signals known as stochastic vestibular stimulation (SVS) have been used along with frequency correlation analysis to probe reflexive responses to continuously varying vestibular inputs. Now, I propose to use this correlation analysis to determine the relationship between angular vestibular input and lower limb activity, without using artificial vestibular stimulation. The vestibular input used in this study will be naturally-occurring; namely, those caused by angular head accelerations in standing sway. These will be measured with a head-mounted 9-accelerometer array, and transformed into angular accelerations acting in the planes of the semi-circular canals. Pilot work has shown that the muscular activity leads angular head accelerations, hinting at the possibility of a feed-forward mechanism from the lower leg to the vestibular system during quiet standing sway. The completion of this thesis may provide further insight into how the vestibular system contributes to standing on a daily basis, and may offer support to the view of standing sway as purposeful exploratory behaviour.
Will Dunlop - Group Diversity & Exercise Adherence
Recent research has suggested that individuals display a general preference for exercising in groups comprised of members of a similar age to themselves and a general dislike for exercising in groups whose members’ age differs from their own. Outside of exercise settings there is also a large body of evidence which suggests that when people perceive themselves to be similar to others, they are more likely to report higher levels of interpersonal attraction. Although age is a salient attribute, there are many other characteristics that may be considered when one is determining the degree of similarity between themselves and others (e.g., gender, attitudes, ect.). The proposed research seeks to identify salient characteristics that influence perceptions of intra-group similarity among members of exercise groups. It is hypothesized that the perceived similarity among group members is initially determined through the assessment of visually accessible traits, referred to as surface-level characteristics (e.g., age, gender, physical condition). This perception of ‘similarity’ is thought to be re-assessed over time using deep-level, non-visually accessible, traits (e.g., attitudes, beliefs, values).The level of perceived similarity among group members may play a key role in their adherence to the exercise class, given that perceptions of intra-group similarity have been found to be positively related to group cohesion. In turn, group cohesion has been found to positively predict member adherence within exercise settings. With this in mind, this study will examine whether group cohesion mediates the relationship between intra-group similarity and exercise adherence.
Jane LaBreche - Exercise Induced Bronchoconstriction in Elite Swimmers
Bronchial vasodilators such as beta 2 agonists are widely used in sport by those suffering from asthma or exercise induced bronchoconstriction. The eucapnic voluntary hyperpnea (EVH) test is an acceptable provocation test by both the Olympic and Paralympic international committees. Athletes with positive tests (a drop of >10% in FEV1) are permitted to use beta 2 agonists during competition in such events. In the sport setting it is considered to be a sensitive test for those with mild symptoms as well those with more obvious symptoms with exercise. As such, it is growing in popularity as a screening tool for athletes in sports which typically involve high ventilations. We tested 12 elite swimmers (National Team members). We found a high incidence of positive tests with large drops in FEV1 in many cases. Most athletes had no history of asthma prior to their swimming careers. With results such as these, we can’t help but ask the question…does swimming cause exercise induced asthma? If so, is this part of a larger issue…does exercise cause asthma?
Brendan Cameron - Online correction to an unperceived target jump modifies motor planning
Rapid online corrections to pointing movements are thought to rely on the motor system’s ability to predict the position of the limb from the outgoing motor command. The error between this forecast and the intended limb position is used to quickly update the movement. We investigated whether this error signal might lead to modification of internal models for the limb, such that the motor commands for subsequent trials compensate for the error at the outset of the movement. Participants pointed to a target that jumped 2.5cm to the right during the orienting saccade and extinguished 200ms later, prior to completion of the pointing movement. Participants completed 45 trials of stationary target (pretest), followed by 120 trials of 100% rightward jumps (acquisition), and then 30 trials of stationary target (posttest). At the start of acquisition, participants’ movements were directed toward the initial target location and then deviated online to the jump location. At the end of acquisition, trajectories were aimed toward the jump location from the onset of the movement. We take this as evidence that, even under normal reaching conditions, an online error signal can drive modification of internal models.
Nicole Ong-Tai-Tee, Alison Bowcock, Nicola J. Hodges - Manipulations to the timing and attentional focus of instructions to examine the reinvestment hypothesis of skill learning
There is evidence that prescriptive versus discovery methods of learning can lead to breakdowns under pressure due to “reinvestment” of knowledge (e.g., Masters & Maxwell, 2004). There is some speculation that this breakdown is mediated by the attentional focus of the instructions. We expected these effects to also be mediated by the timing of the instructions. Three groups practiced a forehand disc throwing task and we manipulated the timing and content of instructions two groups received technical instructions on the first day. Instructions were matched for content but differed in the attentional focus (1 = Internal, body-related; 2 = External, disc-related). A third group only received Internal instructions on a second day (n =10/group). Measures of form and target error were examined in retention and under evaluative conditions (i.e., pressure). Both types of instructions led to improvements in movement form on day 1 compared to no-instructions. However, all groups showed improvedaccuracy across practice (p<.01) and it was the no-instruction group who was the most accurate (significantly different to the Internal group only). In retention, the error scores were similar for the three groups. Under pressure, the External instruction and no-instruction groups’ error was significantly reduced, whereas the Internal instruction group did not make any improvements. All three groups showed a reduction in error on day 2 of practice, although there were no group differences. The form scores of the Internal, day 2 group improved to match that of the other 2 instruction groups. There was Group x Condition interaction when error scores on the delayed retention test were compared to the pressure condition (p <.05). Only participants who received Internal instructions on the first day showed an increase in error under pressure. There is evidence that both the timing and attentional focus of instructions impacts performance under pressure and that these factors interact. Further testing is underway of a day 2, External instruction group to balance the design.
David J. Sanderson, Ryan Cawsey, Scott Apperley, Julia Wilkes - The Effect of Stride-Length Changes on Triceps Surae Excitation During Walking
Sanderson et al. (2006) examined the effect of cadence manipulation on the operating length, velocity of shortening, and triceps surae excitation during cycling at a constant power output. They showed that there was a cadence-sensitivity in gastrocnemius but not soleus and that, at times, the muscles were lengthening and shortening in opposite directions. This study investigated whether these observations were similar in a weight-bearing activity, walking. Our hypothesis was that with increased cadence, there would be increased excitation in both lateral and medial gastrocnemius while soleus excitation would remain insensitive. After determining the preferred walking speed and stride length, participants walked for two minutes at eight randomly presented cadences (85, 90, 95, 100, 105, 110, 115, 120% of preferred cadence) on a treadmill. Sagittal plane 2D kinematics were determined from video recordings of reflective markers placed over bony landmarks of the lower limb. Muscle lengths were calculated from the marker kinematics using equations developed from Hawkins and Hull (1990). These data were differentiated using the central differences method to generate muscle velocities. Surface EMG was recorded from the lateral gastrocnemius, medial gastrocnemius, and soleus muscles. For each condition, ten strides were averaged to create one representative data set per subject. Increasing cadence led to an increase in the integrated EMG from each of the muscles of the triceps surae. The lengths and velocities over which these muscles operated were not significantly affected by the changes in cadence. Both of these findings are contrary to those yielded during cycling. One explanation for this difference could lie in the fact that the foot remains on the floor during walking, whereas during cycling, the pedal is free to rotate. During cycling, one role of the triceps surae is to keep the pedal level and allow for effective transmission of force from the large knee and hip extensor muscles; during walking, the triceps surae provide the majority (80%) of the mechanical power for propulsion. These results suggest that during walking the triceps surae acts with a common purpose not seen in the cycling activity.
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Last reviewed
16-Sep-2008
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