Using principal component analysis to investigate pacing strategies in elite international canoe kayak sprint races.

The aim of this research was to use principal component analysis (PCA) to investigate the current pacing strategies of elite canoe kayak sprint athletes and to determine if there are differences in pacing patterns between medallists and non-medallists at major international competitions. Velocity data collected using global positioning systems (GPS) from all a-finals of major international competitions in 2016-2017 (including canoe and kayak, single and crew boat, and male and female) were downloaded from the International Canoe Federation's website. Data were normalised by the average velocity within each race and organised by race distance. In total 10, 14 and 16 races were analysed, and they followed all-out, positive, and 'seahorse-shaped' pacing strategies for the 200 m, 500 m, and 1000 m events, respectively. Normalised velocity PC1 (p = 0.039, ES = -0.44) and PC2 scores (p < 0.001, ES = -0.73) for 1000 m races were significantly different between medallists and non-medallists; however, significant differences between PCs were not found between groups in shorter race distances (i.e. 200 m and 500 m). Data collected using GPS provide information that can be used to better prepare athletes for canoe kayak sprint races lasting between 30 s and 240 s in duration.

Characterisation of trunk muscle activation amplitude patterns during a simulated checkstand operation with continuously changing flexor and lateral moment demands.

While the typical physical exposure to modern-day workers has changed from heavy to low level repetitive demands, there is limited research that examines light occupations. This study examined trunk muscle recruitment strategies in response to a simulated checkout operation. Surface electromyography and kinematic variables were recorded from 29 healthy subjects. Four principal patterns accounted for 95.3% of the variation. Significant differences in scores captured different strategies in response to reach conditions and external moment directions. Synergistic co-activation of ipsilateral back sites and differential activation among external oblique and erector spinae sites suggests that the central nervous system may control different regions of the trunk musculature to optimally account for asymmetrical demands. The strategy between the internal oblique and back extensor sites suggests that a specific co-activation strategy may be needed during lighter work. During low-load occupational tasks, several recruitment strategies were required to maintain spinal stability and account for changing external moments. STATEMENT OF RELEVANCE: Different recruitment strategies found in response to changing external moments offer new insights into neuromuscular control for lighter work. Specifically, multiple trunk muscle sites interact in a complex manner, taking into account task specificity and individual variation that are valuable in workstation design, evaluating injury risk and estimating spinal loads.

Activation amplitude patterns do not change for back muscles but are altered for abdominal muscles between dominant and non-dominant hands during one-handed lifts.

It is assumed when lifting with the dominant hand that the relationship between contralateral and ipsilateral trunk muscle responses are similar to when lifting with the non-dominant hand. The purpose of this study was to quantify trunk muscle activation amplitude patterns during right- and left-handed lifts. Surface electromyography (EMG) and kinematic variables were recorded from 29 healthy subjects. Minimal trunk and pelvis motion was observed. Three principal patterns accounted for 95% of the variation in the EMG data indicating minimal variation in the pattern. Significant differences in scores captured different recruitment strategies for reach and hand. Selective and differential recruitment of back sites characterized lifts at greater distances from the body, whereas co-activation between internal oblique and back sites characterized lifts closer to the body. While the results showed no handedness effect for back muscles, the external oblique responded differently between right- and left-handed lifts. Specific recruitment strategies were used to account for subtle changes in reach and asymmetrical demands.

Underwater detectibility of a lighting system on a helicopter escape exit.

BACKGROUND: When a helicopter ditches into water, it immediately inverts due to the weight of the engines and then fills with water. Locating the emergency exit for escape under such conditions is a difficult task. A new lighting system for an escape exit has been developed that illuminates on contact with water. The detectibility of the lighting was investigated under varying conditions of ambient illumination, water turbidity, and viewing distance. METHOD: A total of 288 underwater detection trials were carried out by 9 subjects with an illuminated hatch placed at 2 distances (1.5 m and 3.1 m), under 2 ambient illuminations (bright: > 3000 lux and dark: < 0.1 lux), and in 2 conditions of water turbidity. The water temperature was 12 degrees C for all conditions. RESULTS: At 1.5 m, the lighting system was detectable in less than 1.5 s by all subjects in both clear and turbid water and under both bright and dark conditions. At 3.1 m, the lights were detectable in both clear and turbid water under the dark condition and in clear water under the bright condition. However, the lighting was not reliably detected in turbid water under bright condition. CONCLUSIONS: The system met original design requirements in terms of detectibility at 1.5 m. The detection time was always under 1.5 s. It could also be detected at 3.1 m in clear and turbid water, under dark conditions. However, the detectibility at 3.1 m in turbid water, under bright condition was less reliable.

Changes in electromyographic activity of trunk muscles within the sub-acute phase for individuals deemed recovered from a low back injury.

Evidence indicates that previous low back injury (LBI) is a strong predictor for re-injury. The purpose of this study was to examine whether neuromuscular patterns remain altered in a LBI group who were deemed recovered. Surface electromyograms from 12-abdominal and 12-back extensors sites and motion variables were recorded from 33 LBI individuals (sub-acute phase) and 54 asymptomatic controls. Pain-related variables were recorded and a clinical assessment performed for LBI participants. Subjects performed a symmetrical lift and replace task in two reaches. Pattern recognition techniques were applied to normalized activation amplitude patterns to extract key recruitment strategies. Mixed model ANOVAs tested for effects (p < 0.05). Despite similar task performance, significantly (p < 0.05) different recruitment strategies were observed for the LBI group. There were higher activation amplitudes for LBI subjects in all muscles (except posterior external oblique) and greater co-activation between abdominal and back extensor sites compared to controls. Local abdominal and back extensor sites showed altered responses to increased physical demands in the LBI group. Despite outcomes indicating recovery, the LBI group had altered neuromuscular patterns compared to asymptomatic controls supporting that residual alterations remain following recovery.

Activation amplitude and temporal synchrony among back extensor and abdominal muscles during a controlled transfer task: comparison of men and women.

Muscle synergies are important for spinal stability, but few studies examine temporal responses of spinal muscles to dynamic perturbations. This study examined activation amplitudes and temporal synergies among compartments of the back extensor and among abdominal wall muscles in response to dynamic bidirectional moments of force. We further examined whether responses were different between men and women. 19 women and 18 men performed a controlled transfer task. Surface electromyograms from bilateral sites over 6 back extensor compartments and 6 abdominal wall muscle sites were analyzed using principal component analysis. Key features were extracted from the measured electromyographic waveforms capturing amplitude and temporal variations among muscle sites. Three features explained 97% of the variance. Scores for each feature were computed for each measured waveform and analysis of variance found significant (p<.05) muscle main effects and a sex by muscle interaction. For the back extensors, post hoc analysis revealed that upper and more medial sites were recruited to higher amplitudes, medial sites responded to flexion moments, and the more lateral sites responded to lateral flexion moments. Women had more differences among muscle sites than men for the lateral flexion moment feature. For the abdominal wall muscles the oblique muscles responded with synergies related to fiber orientation, with women having higher amplitudes and more responsiveness to the lateral flexion moment than men. Synergies between the abdominal and back extensor sites as the moment demands change are discussed. These findings illustrate differential activation among erector spinae compartments and abdominal wall muscle sites supporting a highly organized pattern of response to bidirectional external moments with asynchronies more apparent in women.

The interpretation of abdominal wall muscle recruitment strategies change when the electrocardiogram (ECG) is removed from the electromyogram (EMG).

The purpose of this study was to determine the effect of the ECG artifact on low-level trunk muscle activation amplitudes and assess the effectiveness of two methods used to remove the ECG. Simulations were performed and percent error in root mean square (RMS) amplitudes were calculated from uncontaminated and contaminated EMG signals at various ECG to EMG ratios. Two methods were used to remove the ECG: (1) filtering by adaptive sampling (FAS) and (2) Butterworth high pass filter at 30 Hz (BW-30 Hz HPF). The percent error was also calculated between the ECG removed and the uncontaminated EMG RMS amplitudes. Next, the BW-30 Hz HPF method was used to remove the ECG from 3-bilateral external oblique (EO) muscle sites collected from 30 healthy subjects performing a one handed lift and replace task. Two separate ANOVA models assessed the effects of ECG on the statistical interpretation of EO recruitment strategies. One model included EMG data that contained the ECG and the other model included EMG data after the ECG was removed. Large percent errors were observed when the ECG was not removed. These errors increased with larger ECG to EMG ratios. Both removal methods reduced the errors to below 10%, but the BW-30 Hz HPF method was more time efficient in removing the ECG artifact. Different statistical findings were observed among the muscle sites for the ECG contaminated model compared to the ECG removed model, which resulted in different conclusions concerning neuromuscular control.

Electromyographic assessment of trunk muscle activation amplitudes during a simulated lifting task using pattern recognition techniques.

This study sought to determine the patterns of neuromuscular response from 24-trunk muscle sites during a symmetrical lift and replace task. Surface electromyograms (EMG) and kinematic variables were recorded from 29 healthy subjects. Pattern recognition techniques were used to examine how activation amplitude patterns changed with the different physical demands of the task (reach, phase of movement). The results indicated that there was very little trunk and pelvis motion during the task. Three principal patterns accounted for 95% of the total variation suggesting that the measured data had a simple underlying structure of variance. ANOVA results revealed significant differences in principal pattern scores. These differences captured subtle changes in muscle recruitment strategies that most likely reflect different stability and biomechanical demands. More balanced activations (bracing) between the abdominal and back sites were observed during the lighter demands, whereas differential recruitment among the back extensor sites was more predominant in the more demanding conditions. A pattern recognition technique offers a novel method to examine the relationships among a large number of muscles and test how different work characteristics change the relationships among the muscle sites.

Changes in trunk muscle activation and lumbar-pelvic position associated with abdominal hollowing and reach during a simulated manual material handling task.

The purpose of this study was to investigate the effect of abdominal hollowing (AH) on trunk muscle activation and lumbar-pelvic motion during a controlled lift and replace task. Surface electromyograms were recorded from five abdominal and two back muscle sites. Sagittal lumbar-pelvic motion was recorded by video. Subjects lifted a 3.8 kg load in normal, maximum and extreme reaches, first while performing their preferred lifting style (PLS) and then maintaining an AH technique. The external oblique muscle site activities were significantly higher (p < 0.05) for the AH technique (ranging from 7-20% of maximal voluntary activation (MVIC)) than at any of the abdominal sites for the PLS (ranging from 2-10% MVIC). Differences were found among abdominal sites for the AH, but not for the PLS. The back muscle site activities (ranging from 9-30% MVIC) were significantly higher (p < 0.05) than for any of the abdominal muscles for all conditions, except for the anterior external oblique for AH. The pelvic and lumbar angles changed significantly (p < 0.05) between normal and maximal reaches and between techniques. The AH technique altered abdominal muscle activation amplitudes, with minimal differences in trunk extensors compared to the PLS. The AH resulted in more posterior pelvic tilt.

The effect of rolling resistance on stationary wheelchair wheelies.

OBJECTIVE: To test the hypotheses that increased rolling resistance (RR) reduces rear-wheel displacement and perceived difficulty during the takeoff and balance phases of stationary wheelchair wheelies. DESIGN: We carried out within-subject comparisons of 20 participants as they each performed, in random order, two 30-sec stationary wheelies in three RR settings (tile, 5-cm-thick foam, and 12.5-cm-high blocks in front of and behind the rear wheels). The main outcome measures were rear-wheel displacement (in centimeters for the takeoff phase and centimeters per second for the balance phase) from a spring-loaded potentiometer and Likert scales of perceived difficulty. RESULTS: For rear-wheel displacement, all six of the pairwise comparisons (three terrains x two phases (takeoff and balance)) showed a significant statistical difference (P < 0.002). In each of the six pairwise comparisons, displacement was less for the higher of the two RR conditions. For perceived difficulty, during the balance phase, participants perceived tile to be significantly more difficult than either foam (P = 0.0067) or blocks (P = 0.0002). The other pairwise comparisons were not statistically significant. CONCLUSION: In conditions of increased RR, rear-wheel displacement and perceived difficulty are reduced during stationary wheelchair wheelies. These findings have implications for teaching wheelchair users to perform wheelies, a foundation of many advanced wheelchair skills.