Michael Hasler

Performance limitation and the role of core temperature when wearing light-weight workwear under moderate thermal conditions.

The objective of this investigation was to achieve an understanding about the relationship between heat stress and performance limitation when wearing a two-layerfire-resistant light-weight workwear (full-clothed ensemble) compared to an one-layer short sports gear (semi-clothed ensemble) in an exhaustive, stressful situation under moderate thermal condition (25°C). Ten well trained male subjects performed a strenuous walking protocol with both clothing ensembles until exhaustion occurred in a climatic chamber. Wearing workwear reduced the endurance performance by 10% (p=0.007) and the evaporation by 21% (p=0.003), caused a more pronounced rise in core temperature during submaximal walking (0.7±0.3 vs. 1.2±0.4°C; p≤0.001) and from start till exhaustion (1.4±0.3 vs. 1.8±0.5°C; p=0.008), accelerated sweat loss (13±2 vs. 15±3gmin(-1); p=0.007), and led to a significant higher heart rate at the end of cool down (103±6 vs. 111±7bpm; p=0.004). Correlation analysis revealed that core temperature development during submaximal walking and evaporation may play important roles for endurance performance. However, a critical core temperature of 40°C, which is stated to be a crucial factor for central fatigue and performance limitation, was not reached either with the semi-clothed or the full-clothed ensemble (38.3±0.4 vs. 38.4±0.5°C). Additionally, perceived exertion did not increase to a higher extent parallel with the rising core temperature with workwear which would substantiate the critical core temperature theory. In conclusion, increased heat stress led to cardiovascular exercise limitation rather than central fatigue.

An approximate simulation model for initial luge track design.

Competitive and recreational sport on artificial ice tracks has grown in popularity. For track design one needs knowledge of the expected speed and acceleration of the luge on the ice track. The purpose of this study was to develop an approximate simulation model for luge in order to support the initial design of new ice tracks. Forces considered were weight, drag, friction, and surface reaction force. The trajectory of the luge on the ice track was estimated using a quasi-static force balance and a 1d equation of motion was solved along that trajectory. The drag area and the coefficient of friction for two runs were determined by parameter identification using split times of five sections of the Whistler Olympic ice track. The values obtained agreed with experimental data from ice friction and wind tunnel measurements. To validate the ability of the model to predict speed and accelerations normal to the track surface, a luge was equipped with an accelerometer to record the normal acceleration during the entire run. Simulated and measured normal accelerations agreed well. In a parameter study the vertical drop and the individual turn radii turned out to be the main variables that determine speed and acceleration. Thus the safety of a new ice track is mainly ensured in the planning phase, in which the use of a simulation model similar to this is essential.

Viscose as an alternative to aramid in workwear: Influence on endurance performance, cooling, and comfort

Workwears are required to maintain optimum performance during dangerous, exhausting activities (e.g. those involving the fire brigade or police). The purpose of the present study was to compare two workwears (A and B) composed of underwear and outerwear with different fiber blends (A: 100% aramid; B: combination of fire resistant (FR) viscose/merino wool underwear and FR viscose/aramid outerwear) during strenuous physical activity. In a climatic chamber (25℃, 50% RH) participants had to walk on a treadmill until exhaustion occurred. Weight measurements were made for calculating evaporation, sweat residue, and sweat distribution. Endurance performance was assessed by time to exhaustion. Core temperature, heart rate, lactate, thermal comfort, microclimate between skin and underwear, surface temperature of the outerwear, and perceived exertion were also measured. The tested workwears caused no significant differences in time to exhaustion, core temperature, and thermal comfort. Sweat distribution differed significantly in the workwears. The underwear of workwear B caused less moisture accumulation in the outerwear and this may be a beneficial safety feature for the prevention of hazardous burns of the skin. Moisture accumulation in the outerwear may reduce thermal insulation and increase the possibility of evaporation whereby hot steam may move to the skin. The potential protective feature of the FR viscose/merino wool blended underwear and the economical price of viscose support the use of fire resistant (FR) viscose blended fabrics in workwears.

Friction Between Ski and Snow

The first skis were developed to improve locomotion across the natural, wind packed snow surface in the European northern countries. The skis were made of flat planks with shovels at the tips. Under load, the tips and ends of the skis bended up causing resistance against forward movement. An improvement of the gliding of skis was the invention of the bow-shaped cambered ski, arched up towards his center. Under load, the ski lies flat on the snow surface and the load is more evenly distributed along the ski. With the appearance of downhill skiing, the turning properties of skis became more important. In 1928, Lettner (AT) invented steel edges to give the skis more grip. During the first half of the twentieth century, the technique was developed to produce laminated skis composed of a wooden core with different bottom and upper layers. In 1955, Kofler (AT) introduced the first ski with a polyethylene base, which remarkably improved the gliding properties. In addition, the repair of minor scratches was easily possible. In the recent past, the gliding properties of skis were further developed by special grinding techniques for the ski base and by the development of special waxes.

Eccentric Exercise, Kinesiology Tape, and Balance in Healthy Men

CONTEXT   Deficits in balance have been identified as a possible risk factor for knee injuries in athletes. Despite a lack of evidence for its effectiveness, kinesiology tape (KT) is widely used to prevent knee injuries. OBJECTIVE   To investigate the influence of KT at the knee joint on balance ability in healthy men after eccentric exercise. DESIGN   Crossover study. SETTING   University laboratory. PATIENTS OR OTHER PARTICIPANTS   Twelve young men with no history of lower limb injury volunteered for the study (age = 23.3 ± 2.6 years). All participants were students enrolled in a sports science program. INTERVENTION(S)   Participants performed the balance test with and without KT at the knee joint on 2 separate days. MAIN OUTCOME MEASURE(S)   The ability to maintain balance was assessed during a single-legged-stance test using a computerized balance-stability test system. The test was performed before and after 30 minutes of downhill walking on a treadmill. RESULTS   Eccentric exercise resulted in a deterioration of balance ability, which was attenuated by the use of KT. Further analyses revealed that the effectiveness of KT depended on the participants balance status, with the preventive effect being greater in participants presenting with poorer baseline balance ability. CONCLUSIONS   Applied to the knee joint, KT counteracted the exercise-related deterioration of balance ability observed when no tape was used. Participants presenting with below-average balance ability received more benefit from KT. By preventing exercise-related impairment of balance ability, KT might help to reduce the risk of sport-associated knee injuries.

The Effect of Uphill and Downhill Walking on Joint-Position Sense: A Study on Healthy Knees

CONTEXT During sport activity, knee proprioception might worsen. This decrease in proprioceptive acuity negatively influences motor control and therefore may increase injury risk. Hiking is a common activity characterized by a higher-intensity-exercise phase during uphill walking and a lower-intensity-exercise phase during downhill walking. Pain and injuries are reported in hiking, especially during the downhill phase. OBJECTIVE To examine the effect of a hiking-fatigue protocol on joint-position sense. DESIGN Repeated measures. SETTING University research laboratory. PARTICIPANTS 24 nonprofessional sportswomen without knee injuries. MAIN OUTCOME MEASURES Joint-position sense was tested at the beginning, after 30 min uphill walking, and after 30 min downhill walking on a treadmill (continuous protocol). RESULTS After downhill walking, joint-position sense was significantly worse than in the test at the beginning (P = .035, α = .05). After uphill walking, no differences were observed in comparison with the test at the beginning (P = .172, α = .05) or the test after downhill walking (P = .165, α = .05). CONCLUSION Downhill walking causes impairment in knee-joint-position sense. Considering these results, injury-prevention protocols for hiking should focus on maintaining and improving knee proprioception during the descending phase.

Effects of two different battings (sheep wool versus polyester microfiber) in an outdoor jacket on the heat and moisture management and comfort sensation in the cold

Wool in outdoor clothing systems is stated to be a good temperature and humidity regulator giving the wearer a warm and dry feeling during physical activities in the cold. The objective was to compare two different battings (sheep wool “tirolwool” (TW) versus polyester microfiber (PMF)) in an outdoor jacket of a two-layer outdoor clothing system consisting of a shirt and jacket on the heat and moisture management and comfort sensation during a moderate mountain walking protocol which was followed by a cool-down phase in the cold (−5℃, 43% relative humidity). Due to its beneficial moisture management properties it was hypothesized that TW in the outermost layer would cause a higher skin and core temperature, reduce the after chill effect, increase moisture transfer, decrease moisture accumulation within the clothing system, and lead to more pleasant comfort sensations. Twelve sport students performed the simulated walking protocol (60 min, 7.7% inclination, 5 km/h) and cool-down phase (20 min) with TW and PMF in a climatic chamber. The use of TW compared to PMF was stronger moisture absorbent led to a dryer shirt (p = 0.043) and lower humidity underneath the shirt and jacket (chest: p ≤ 0.05). Core temperature (p = 0.017) and skin temperature drop (chest: p = 0.003) were attenuated with TW after the physical activity. Therefore, the after chill effect was reduced with TW but moisture accumulated to a higher extent in the jacket (p = 0.001), which might lead to a longer drying rate. Correlation analysis revealed that tested underwear blended with merino wool, elastane, and polyamide might feel less scratchy in the slightly damp state than in the dry state.

The effect of different water vapor permeable jackets on moisture management, subjective perceptions and physiological parameters during submaximal exercise in a cool environment:

The goal of this study was to investigate the effect of differences in water vapor permeability (WVP) of outdoor jackets on moisture management, subjective perceptions and physiological parameters under conditions typically encountered in outdoor sports. Four outdoor jackets differing only in their WVP were compared in a repeated measures study. A total of 19 subjects (nine females) were tested in a climatic chamber at 10℃ and 40% relative humidity. The protocol consisted of 15 min of rest, 50 min of treadmill running at 60% of the individual maximal running velocity, and 15 min of passive recovery. We found that jackets featuring greater WVP helped to reduce relative humidity underneath the jacket, resulting in less sweat residue in the clothing system and drier skin during exercise and rest. Subjects were also able to perceive the differences in the microclimate and reported feeling more comfortable and drier in the more permeable jackets. However, WVP did not have a significant effect on oxygen consumption, heart rate, tympanic temperature, overall loss of subjects’ body mass or on perceived exertion. It can be concluded that outdoor jackets with higher WVP benefit moisture management during submaximal exercise in cool temperatures by reducing relative humidity in the clothing system mostly during rest periods. This effect leads to a drier skin which favors perceived comfort and might reduce the after-chill effect. However, WVP of outdoor jackets neither significantly affects physiological responses nor perceived exertion during submaximal exercise in a cool environment.

Does Kinesiology tape counter exercise-related impairments of balance in the elderly?

BACKGROUND Maintaining balance is an essential requirement for the performance of daily tasks and sporting activities, particularly in older adults to prevent falls and associated injuries. Kinesiology tape has gained great popularity in sports and is frequently used as a tool for performance enhancement. However, there is little research investigating its influence on balance. RESEARCH QUESTION The purpose of this study was to evaluate the effect of Kinesiology tape on dynamic balance, postural stability and knee proprioception after physical activity in healthy, older adults. METHODS Twelve physically active, healthy men aged 63-77 years performed the test on two separate days, with and without Kinesiology tape at the knee joint (prospective intervention with cross-over design). Dynamic balance during an obstacle-crossing task, postural stability in a single-leg stance test, and knee joint position sense as a measure of proprioception were examined before and after 30 min of downhill walking on a treadmill. The influences of taping condition and physical activity on all parameters were statistically tested using factorial ANOVAs. RESULTS Factorial ANOVA revealed significant time × taping condition interaction effects on all performance parameters (p < 0.05), indicating that the exercise-related changes in dynamic balance, postural stability and knee proprioception differed between the two taping conditions. The deterioration of performance was always greater when no tape was used. SIGNIFICANCE This study demonstrated that physical exercise significantly deteriorated dynamic balance, postural stability and knee proprioception in older men. These effects can be attenuated through the usage of Kinesiology tape. By preventing exercise-related impairments of balance, Kinesiology tape might help reduce the risk of sports-associated falls and associated injuries.

Effects of functional shirts with different fiber compositions on thermoregulation in well-trained runners:

This study aimed to investigate the effects of two functional sport shirts with different fiber compositions (polyester: 100% polyester vs polyester–lyocell combination: 67%–33%) on thermoregulation and wearing comfort during treadmill walking at an average intensity under moderate environmental conditions. It was hypothesized that the hydrophilic lyocell fibers would benefit sweat evaporation and, thus, provide a superior cooling effect. Using a repeated-measures study design, core, surface and between skin-and-shirt temperatures were measured in 11 men while wearing either the polyester or polyester–lyocell shirt. Additionally, sweat loss, heart rate and subjective perception of comfort were determined. In spite of significantly greater sweat production, relative humidity was lower with the polyester–lyocell shirt. In the later phases of the walking intervention, the temperatures were consistently higher with polyester–lyocell, although between-shirt differences failed to reach significance. These results suggest that greater water retention limits the thermoregulatory efficiency of cellulosic fibers when excessive sweat production occurs.