Scott P McLean

Impacts and kinematic adjustments during an exhaustive run.

PURPOSE To examine the kinematic adjustments that runners make during an exhaustive run and to look at the effects these adjustments have on shock and shock attenuation. METHODS Ten recreational runners ran to volitional exhaustion on a treadmill at a velocity equal to their average 3200-m running velocity at maximal effort (average time: 15.7 +/- 1.7 min). Head and leg accelerometers, a knee electrogoniometer, and a rearfoot electrogoniometer were attached to each subject. The data were sampled at 1000 Hz at the start, middle, and end of the run. RESULTS The knee became significantly more flexed at heel impact (start: 164.9 +/- 2.3 degrees; end: 160.5 +/- 2.9 degrees; P < 0.05). The rearfoot angle became more inverted at impact (start: 12.2 +/- 1.6 degrees; end: 13.6 +/- 1.9 degrees; P < 0.05). These kinematic changes resulted in a lower extremity that that had a lower effective mass during the impact. This decreased effective mass allowed the leg to accelerate more easily; thus, peak leg impact accelerations (start: 6.11 +/- 0.96 g; end: 7.38 +/- 1.05 g; P < 0.05) and impact attenuation (start: 74.5 +/- 5.4%; end: 77.5 +/- 4.1%; P < 0.05) increased during the progression of the run. CONCLUSIONS The increase in peak impact accelerations at the leg was not considered an increased injury risk because of the decreased effective mass. The altered kinematics may have resulted in increased metabolic costs during the latter stages of the exhaustive run.

Electromechanical delay in isometric actions initiated from nonresting levels.

PURPOSE The purpose of this study was to determine whether electromechanical delay (EMD) was associated exclusively with the onset of tension from a resting state and whether EMD remained constant across different rates of force development. METHODS Twenty-four subjects (23.9 +/- 5.4 yr, 171.7 +/- 7.3 cm, 72.9 +/- 12.8 kg) performed isometric elbow flexion trials in the transverse plane by using the dominant arm during which isometric force data and surface EMG activity were collected. Subjects completed three trials to establish a maximal force (MF) reference. Subjects then completed trials in which pulse forces of varying magnitudes were elicited at a frequency of 1 Hz from different baseline intensities. All forces were expressed relative to MF. Three trials of the following conditions (baseline-pulse) were performed in random order: 0-25%, 25-50%, 50-75%, 0-50%, and 0-75%. EMG and force data were collected for 10 pulse cycles during these trials. EMD was defined as the temporal shift that maximized a normalized cross-correlation function. RESULTS EMD for a 25% pulse force developed from rest (83.5 +/- 12.9 ms) was significantly longer than that developed from 25% (66.3 +/- 11.5 ms) or 50% (60.6 +/- 16.6 ms) baselines. EMD values were not different when force was developed from 25% and 50% baselines. EMD associated with a 25% pulse force from rest was significantly longer than 50% (70.3 +/- 10.0 ms) and 75% (68.9 +/- 8.7 ms) pulse forces from rest. EMD for 50% and 75% pulse forces from rest were not statistically different. CONCLUSION It was concluded that EMD is present during exertions initiated from both resting and nonresting states but is reduced when exertions are initiated from non-resting states and with higher rates of force development.

Sex differences in the centre of buoyancy location of competitive swimmers

The aims of this study were to identify differences in the centre of buoyancy (CB) and centre of mass (CM) locations of male and female collegiate swimmers, and to assess the influence that buoyancy has on freestyle kicking performance. Sixteen female collegiate swimmers (mean +/- s: age 19.1 +/- 1.2 years) had significantly more adipose tissue (20.2 +/- 4.4%) than 15 male collegiate swimmers (19.9 +/- 1.0 years, 12.6 +/- 3.8%). The ratio of the sum of abdominal and suprailiac skinfolds to the thigh skinfold was significantly greater for the males (2.07 +/- 0.37) than the females (1.31 +/- 0.32), implying that females had proportionately more fatty tissue caudally than males. The distance d between the centres of buoyancy and mass was significantly larger for the males (0.79 +/- 0.43 cm) than the females (0.16 +/- 0.34 cm). Both points were more caudal in the female subjects (59.9 +/- 0.7% and 59.8 +/- 0.7% of body height respectively) than in the male subjects (61.7 +/- 0.8% and 61.2 +/- 0.9% respectively). These data suggest that the difference in d may be attributed to the difference in the location of the centre of buoyancy, because the centre of mass difference was not significant and was characterized by a smaller effect size. The amount and distribution of adipose tissue accounted for a significant proportion of variance in d (R2 = 0.25 and 0.29 respectively). Males had a significantly higher proportional kick time, defined as the ratio of times to complete a 22.9 m sprint when kicking and swimming respectively, than females (1.57 +/- 0.09 and 1.51 +/- 0.13 respectively). This shows that the male swimmers kicked proportionally more slowly than the female swimmers. However, the distance d did not account for a significant proportion of variance in the proportional kick time. Therefore, our results do not support the notion that skilled male swimmers are at a performance disadvantage in terms of natural buoyancy characteristics.

NLT and extrapolated DLT: 3-D cinematography alternatives for enlarging the volume of calibration

This study investigated the accuracy of the direct linear transformation (DLT) and non-linear transformation (NLT) methods of 3-D cinematography/videography. A comparison of standard DLT, extrapolated DLT, and NLT calibrations showed the standard (non-extrapolated) DLT to be the most accurate, especially when a large number of control points (40-60) were used. The NLT was more accurate than the extrapolated DLT when the level of extrapolation exceeded 100%. The results indicated that when possible one should use the DLT with a control object, sufficiently large as to encompass the entire activity being studied. However, in situations where the activity volume exceeds the size of ones DLT control object, the NLT method should be considered.

Submaximal Expression of the Bilateral Deficit

Thirty-six participants performed bilateral and unilateral isometric elbow flexion trials at what they perceived to be 100, 75, 50, and 25% of maximal effort. Absolute bilateral deficits ranged from -16% at 25% effort to -10% at 100% effort. The deficit included a component independent of consciousness and a component inversely related to intensity attributable to perceptual differences between unilateral and bilateral tasks. Forty-two participants performed bilateral and unilateral isometric elbow flexion trials at 100, 80, 60, 40, and 20% of maximal effort. Perception of effort in submaximal bilateral trials was consistently and significantly higher (5.5-9.6%) than corresponding unilateral trials. These data suggest that the bilateral deficit exists at submaximal levels of effort and is based on perceptual and physiological components.

Oxygen uptake response to stroke rate manipulation in freestyle swimming.

UNLABELLED During gait, humans choose a combination of step length and step rate that minimizes V˙O2. However, little work has been reported on the existence of such optimization in swimming. PURPOSE The purpose of this study was to examine the manipulation of stroke rate on V˙O2 in submaximal, constant speed freestyle swimming. METHODS Preferred stroke rate for swimming freestyle at 1.0 m·s(-1) in a flume was determined for 10 competitive swimmers (mean ± SD: age = 33.3 ± 13.6 yr, height = 175.3 ± 8.6 cm, weight = 74.9 ± 12.2 kg). Participants then completed flume swims at 1.0 m·s(-1) with stroke rates equal to -20%, -10%, 0%, +10%, and +20% of their preferred stroke rate in a randomized order during which V˙O2 was continuously monitored. Each trial continued for 1 min after steady-state V˙O2 was verified (∼4-5 min). During the final minute of each trial, V˙O2 was measured using the Douglas bag technique, HR was recorded, and kick rate (KR) was computed using the time needed to complete 30 kicks. RPE was reported immediately after each trial. RESULTS V˙O2 increased 11%-16% (P < 0.05) when stroke rate was reduced but was nominally affected when stroke rate was increased. Likewise, HR increased 4%-6% (P < 0.05), and RPE increased 15%-30% (P < 0.05) when stroke rate was reduced but not affected when stroke rate was increased. CONCLUSIONS These data suggest that these swimmers preferred to swim freestyle at the lowest stroke rate (or the longest stroke length) that did not require an increase in V˙O2.

Influence of Arm Position and Lung Volume on the Center of Buoyancy of Competitive Swimmers

Interest in buoyancy has persisted, because understanding this force may aid areas of aquatics, including developmental swimming, aquatics rescue, and competitive swimming. Descriptions of buoyancy characteristics and their influence on swimming have been predicated in the popular literature based on logic, intuition, and limited experimental results. The artificial manipulation of buoyancy has demonstrated that buoyancy has a meaningful influence on swimming performance, including reductions in swim time, energy cost, and drag forces (Capelli et al., 1995; Chatard, Senegas, Selles, Dreanot, & Geyssant, 1995; Cordain & Kopriva, 1991; Toussaint, et aI., 1988; Zamparo, Capelli, Termin, Pendergast, & di Prampero, 1996). Understanding the influence of buoyancy on swimming performance is incomplete, because few studies have directly examined natural buoyancy and even fewer have related these data to performance. Zamparo, Antonutto, et al. (1996) suggested that narrowing the performance gap in long distance swimming races was a result of more favorable natural buoyancy characteristics in women, but based their conclusions on buoyancy data and performance data collected from different participants. McLean and Hinrichs (1998) found little relationship of a single measurement of the distance (d) between the center of buoyancy (CB) and center of mass (CM) with swimming performance. Chatard, Collornp,

Do wrist orthoses cause compensatory elbow and shoulder movements when performing drinking and hammering tasks

Purpose Wrist orthoses are used by occupational therapists to decrease pain, support weak muscles and protect tissues during healing. However, use of wrist orthoses has been observed to produce compensatory movements in other upper extremity joints. This paper aims to determine whether wearing wrist orthoses produced compensatory movements of the elbow in addition to the shoulder when performing drinking and hammering tasks. Design/methodology/approach Two twin-axis electrogoniometers were positioned on the elbow and shoulder to track joint movement. The four conditions were drink with orthosis, hammer with orthosis, drink without orthosis and hammer without orthosis. Joint movement was defined as total angular excursion of the joint throughout the performance of the task. Separate 2 × 2 (joint × orthosis) repeated measures analyzes of variance (ANOVA) were used to evaluate differences in joint excursion of the elbow and shoulder joints between orthosis conditions for each task. Findings Wearing a wrist orthosis did not change the amount of joint excursion compared to not wearing an orthosis during the drinking and hammering tasks. Originality/value Findings suggest that wrist orthoses do not result in statistically significant changes in elbow and shoulder joint movements during simulated drinking and hammering tasks.