Micro-biopsies: a less invasive technique for investigating human muscle fiber mechanics

The purpose of this investigation was to demonstrate that muscle fiber mechanics can be assessed on micro-biopsies obtained from human medial gastrocnemii. Three micro-biopsy samples were collected from female dancers (n=15). Single fibers and fiber bundles were isolated and passively stretched from 2.4 µm to 3.0 µm at 0.015 µm•s−1 and 0.04 µm•s−1 (n=50 fibers total) and in five increments at 0.12 µm•s−1 (n=42 fibers total). Muscle fibers were then activated isometrically at 2.4 µm (n=4 fibers total) and 3.0 µm (n=3 fibers total). Peak stress and steady state stress were significantly greater (p<0.0001) after stretching at 0.04 µm•s−1 than 0.015 µm•s−1. Furthermore, peak stresses and steady state stresses increased non-linearly with fiber length (p<0.0001). We conclude that active and passive muscle fiber mechanics can be investigated using tissue from micro-biopsies.

Pacing and stroke kinematics in 200-m kayak racing

Pacing profiles of 19 elite and sub-elite 200-m kayak athletes were examined through stroke-by-stroke analysis, using GPS/accelerometer methodology. Stroke rates and lengths were also quantified across multiple race segments. Whilst athletes reached peak velocity at between 40 and 60 m, it was not possible to determine specifically whether an all-out or positive strategy was employed. Race times were strongly and negatively correlated with the acceleration over the first ~25% of race distance (r = -0.95 ± 0.04) as well as average velocity over the first 30 m of the race (r>-0.9), i.e. faster starts were associated with faster finishing times. Furthermore, the maintenance of velocity, stroke rate and stroke length after reaching their maxima were strongly associated with race times. Stroke rates were higher (Cohen's d = 5.19) in the elite than sub-elite athletes (group categorisation based on race times), but there were no substantial differences in stroke rates between athletes within the elite cohort. Nonetheless, longer stroke lengths were associated with faster race times within the elite cohort (r = -0.48 to -0.85). The current study suggests that faster rates of acceleration and the ability to exhibit greater stroke lengths at relatively high stroke rates are determinants of 200-m kayak race performance.

Running economy and effort after cycling: Effect of methodological choices

Prior exercise can negatively affect movement economy of a subsequent task. However, the impact of cycling exercise on the energy cost of subsequent running is difficult to ascertain, possibly because of the use of different methods of calculating economy. We examined the influence of a simulated cycling bout on running physiological cost (running economy, heart rate and ventilation rates) and perceptual responses (ratings of perceived exertion and effort) by comparing two running bouts, performed before and after cycling using different running economy calculation methods. Seventeen competitive male triathletes ran at race pace before and after a simulated Olympic-distance cycling bout. Running economy was calculated as V̇O₂ (mL∙kg^-1∙min^-1), oxygen cost (EO₂, mL∙kg^-1∙m^-1) and aerobic energy cost (E_aer, J∙kg^-1∙m^-1). All measures of running economy and perceptual responses indicated significant alterations imposed by prior cycling. Despite a good level of agreement with minimal bias between calculation methods, differences (p < 0.05) were observed between E_aer and both V̇O₂ and EO₂. The results confirmed that prior cycling increased physiological cost and perceptual responses in a subsequent running bout. It is recommended that E_aer be calculated as a more valid measure of running economy alongside perceptual responses to assist in the identification of individual responses in running economy following cycling.

Sodium bicarbonate ingestion increases glycolytic contribution and improves performance during simulated taekwondo combat

PURPOSE

To investigate the effect of sodium bicarbonate (NaHCO₃) on performance and estimated energy system contribution during simulated taekwondo combat.

METHODS

Nine taekwondo athletes completed two experimental sessions separated by at least 48 h. Athletes consumed 300 mg/kg body mass of NaHCO₃ or placebo (CaCO₃) 90 min before the combat simulation (three rounds of 2 min separated by 1 min passive recovery), in a double-blind, randomized, repeated-measures crossover design. All simulated combat was filmed to quantify the time spent fighting in each round. Lactate concentration [La^-] and rating of perceived exertion (RPE) were measured before and after each round, whereas heart rate (HR) and the estimated contribution of the oxidative (W_OXI), ATP (adenosine triphosphate)-phosphocreatine (PCr) (W_PCR), and glycolytic (W_[La^-]) systems were calculated during the combat simulation.

RESULTS

[La^-] increased significantly after NaHCO₃ ingestion, when compared with the placebo condition (+14%, P = 0.04, d = 3.70). NaHCO₃ ingestion resulted in greater estimated glycolytic energy contribution in the first round when compared with the placebo condition (+31%, P = 0.01, d = 3.48). Total attack time was significantly greater after NaHCO₃ when compared with placebo (+13%, P = 0.05, d = 1.15). W_OXI, W_PCR, VO₂, HR and RPE were not different between conditions (P > 0.05).

CONCLUSION

NaHCO₃ ingestion was able to increase the contribution of glycolytic metabolism and, therefore, improve performance during simulated taekwondo combat.

The Effects of Either a Mirror, Internal or External Focus Instructions on Single and Multi-Joint Tasks

Training in front of mirrors is common, yet little is known about how the use of mirrors effects muscle force production. Accordingly, we investigated how performing in front of a mirror influences performance in single and multi-joint tasks, and compared the mirror condition to the established performance effects of internal focus (IF) and external focus (EF) instructions in a two part experiment. In the single-joint experiment 28 resistance-trained participants (14 males and 14 females) completed two elbow flexion maximal voluntary isometric contractions under four conditions: mirror, IF, EF and neutral instructions. During these trials, surface EMG activity of the biceps and triceps were recorded. In the multi-joint experiment the same participants performed counter-movement jumps on a force plate under the same four conditions. Single-joint experiment: EF led to greater normalized force production compared to all conditions (P≤0.02, effect-size range [ES] = 0.46–1.31). No differences were observed between neutral and mirror conditions (P = 0.15, ES = 0.15), but both were greater than IF (P<0.01, ES = 0.79–1.84). Surface EMG activity was comparable across conditions (P≥0.1, ES = 0.10–0.21). Multi-joint experiment: Despite no statistical difference (P = 0.10), a moderate effect size was observed for jump height whereby EF was greater than IF (ES = 0.51). No differences were observed between neutral and mirror conditions (ES = 0.01), but both were greater than IF (ES = 0.20–22). The mirror condition led to superior performance compared to IF, inferior performance compared to EF, and was equal to a neutral condition in both tasks. These results provide novel and practical evidence concerning mirror training during resistance type training.

A Descriptive Physical Profile of Western Australian Male Paramedics

Introduction The purpose of this investigation was to evaluate the physical characteristics of a group of West Australian male paramedics. Methods Data was collected from conventional (CO) (n=18) and special operations (SO) (n=11) officers undergoing occupational performance evaluations as contracted by St. John Ambulance Australia to an external independent third party. Using a series of field-based physical conditioning tests, aerobic capacity (multistage shuttle run test), body composition (skinfolds), flexibility (sit-and-reach test), muscular strength (5 stage abdominal and grip strength), muscular endurance (sit-ups, push-ups and chin-ups in 60 seconds (s)), power (vertical jump height), and anaerobic capacity/agility using the Bangsbo agility test were examined. Results The average predicted aerobic capacity of all officers was 45.8±5.2 ml·kg·min-1 (mean ± SD). Mean rating of abdominal strength was 4±1 and mean grip strength was 52±9 kg. The maximum number of sit-ups, push-ups and chin-ups performed in 60 s was 21±11, 40±12 and 7±5, respectively. Significantly more push-ups were completed for SO than for CO. Percentage body fat was significantly lower for SO than for CO. Fatigue index score (Bangsbo test) were significantly lower for SO than for CO. Conclusion The physical fitness profile of our sample indicated above normal levels of aerobic capacity, local muscle endurance and muscle strength, which likely contributes to workplace performance competency. However the fitness profile highlighted a potential deficiency in anaerobic capacity. Paramedics may benefit from a physical conditioning program with emphasis on their ability to operate at a greater functional capacity for higher repeated near maximal efforts.

Performance factors in the new combined event of modern pentathlon

The aims of this study were to determine (1) the individual tactics employed by elite modern pentathletes within each discipline of the new combined running-shooting event, and (2) the consequences of these strategies on overall performance. For 36 male pentathletes competing in a World Cup event, we measured running velocity, transition time, shooting time, shooting accuracy, and delay per shot. Performances of the top third of athletes, middle third of athletes, and the bottom third of athletes in the combined event were compared. The difference in overall performance between the top third and middle/bottom thirds was predominately associated with better shooting accuracy (79 +/- 13%, 68 +/- 12%, and 64 +/- 10% success rate for top, middle, and bottom third, respectively) and faster shooting time (86 +/- 16 s, 109 +/- 19 s, and 117 +/- 23 s for top, middle, and bottom third, respectively). No significant differences in running velocity, transition time or delay per shot were observed among the three groups. All the competitors started significantly faster over the first 200 m of each of the three 1-km running stages. The last third of the approximately 3-km race was completed significantly faster by all athletes (P < 0.05). The main finding was that the best performers of the combined event distinguished themselves due to their greater shooting accuracy.