A study on exposure to ultraviolet rays during outdoor sports activity

1. 1. Intensities of ultraviolet rays (UV) from every direction and the amount of UV absorbed by each body part was measured in four situations (track, beach, golf course and skiing slope).

2. 2. The intensity of UV was measured by a portable UV meter and the amount of UV absorbed by every body part was measured with a UV irradiation energy measurement label.

3. 3. The intensity of UV was strong from S45° and SE45° in all cases. On snow, the intensity of UV from every direction was stronger than in other situations, it was especially strong in reflection from below and from the north. The UV reflection from the sand was slightly larger than that from mud and grass.

4. 4. The experimental day's weather was fine and occasionally cloudy during golf, beach activity and gate-ball, and clear during skiing.

5. 5. The UV deal of a horizontal plane was 135, 98, 156 and 120 kJ/m²/h at golf, beach activity, gate-ball and skiing, respectively.

6. 6. This study suggests that players should be concerned with the prevention of UV radiation during sporting activity.

Muscle response times between shoe and no-shoe conditions following a weight-bearing rotary perturbation are similar in females

The purpose of this study was to compare the muscle response times (MRTs) of select lower extremity muscles following a weight bearing rotary perturbation in single-leg stance with and without shoes. Ten recreationally active females volunteered for this study. Each subject received a rotary perturbation in single-leg stance under two conditions: with shoes and without shoes. The outcomes measured were response times of the medial and lateral quadriceps, hamstrings and gastrocnemius. The results demonstrated that significant differences in MRTs were not apparent for either the medial or lateral perturbation between conditions. While a main effect for muscle was evident for both medial and lateral perturbations, a muscle by shoe interaction was not present for either the medial or lateral perturbation. Our findings suggest that wearing shoes does not alter MRTs during single-limb rotary perturbations. These data indicate that lower extremity perturbation device testing may be done with or without shoes and comparisons between works are permissible as response times are unaffected.     

Effects of starvation and desiccation on energy metabolism in desert and mesic Drosophila

Energy availability can limit the ability of organisms to survive under stressful conditions. In Drosophila, laboratory experiments have revealed that energy storage patterns differ between populations selected for desiccation and starvation. This suggests that flies may use different sources of energy when exposed to these stresses, but the actual substrates used have not been examined. We measured lipid, carbohydrate, and protein content in 16 Drosophila species from arid and mesic habitats. In five species, we measured the rate at which each substrate was metabolized under starvation or desiccation stress. Rates of lipid and protein metabolism were similar during starvation and desiccation, but carbohydrate metabolism was several-fold higher during desiccation. Thus, total energy consumption was lower in starved flies than desiccated ones. Cactophilic Drosophila did not have greater initial amounts of reserves than mesic species, but may have lower metabolic rates that contribute to stress resistance.     

Human locomotion on snow: determinants of economy and speed of skiing across the ages

We explore here the evolution of skiing locomotion in the last few thousand years by investigating how humans adapted to move effectively in lands where a cover of snow, for several months every year, prevented them from travelling as on dry ground. Following historical research, we identified the sets of skis corresponding to the 'milestones' of skiing evolution in terms of ingenuity and technology, built replicas of them and measured the metabolic energy associated to their use in a climate-controlled ski tunnel.Six sets of skis were tested, covering a span from 542 AD to date. Our results show that: (i) the history of skiing is associated with a progressive decrease in the metabolic cost of transport, (ii) it is possible today to travel at twice the speed of ancient times using the same amount of metabolic power and (iii) the cost of transport is speed-independent for each ski model, as during running. By combining this finding with the relationship between time of exhaustion and the sustainable fraction of metabolic power, a prediction of the maximum skiing speed according to the distance travelled is provided for all past epochs, including two legendary historical journeys (1206 and 1520 AD) on snow. Our research shows that the performances in races originating from them (Birkebeiner and Vasaloppet) and those of other modern competitions (skating versus classical techniques) are well predicted by the evolution of skiing economy. Mechanical determinants of the measured progression in economy are also discussed in the paper.     

Identification of knee joint models for varus-valgus and internal-external rotations: snow skiing experiments

Sprains at the knee are the most frequent of the severe injuries occurring during alpine snow skiing. This paper discusses the development of analytical models describing rotations across the knee joint caused by varus-valgus and internal-external moments applied at the foot during skiing. Identification of an ARMAX model requires simultaneous measurements of the rotations across the knee and the moments at the foot during skiing. As the models only relate the measured input (moment) and output (rotation) data, they also identify components of apparent rotation resulting from imperfect fixation of the rotation measuring instrument on the test subject and resulting from other inputs. The models identified for all subjects are of order four or five for both varus-valgus and internal-external rotation, and they describe modes with oscillatory and exponentially decaying components. Application of the models to prediction of rotation across the knee from the measured moment at the foot is illustrated by example. A new, and virtually mechanically uncoupled, six degrees-of-freedom, strain gauge dynamometer is developed to record the moments at the foot during skiing. The concept of the dynamometer design has general application.     

Muscle activity in the leg is tuned in response to impact force characteristics

Based on results from quasi-static experiments, it has been suggested that the lower extremity muscle activity is adjusted in reaction to impact forces with the goal of minimizing soft-tissue vibrations. It is not known whether a similar muscle tuning occurs during dynamic activities. Thus, the purpose of this study was to determine the effect of changes in the input signal on (a) vibrations of lower extremity soft-tissue packages and (b) EMG activity of related muscles during heel-toe running. Subjects performed heel-toe running in five different shoe conditions. Ground reaction forces were measured with a KISTLER force platform, soft-tissue vibrations were measured with tri-axial accelerometers and muscle activity was measured using surface EMG from the quadriceps, hamstrings, tibialis anterior and triceps surae groups from 10 subjects. By changing both the speed of running and the shoe midsole material the impact force characteristics were changed. There was no effect of changes in the input signal on the soft-tissue peak acceleration following impact. A significant correlation (R2=0.819) between the EMG pre-activation intensity and the impact loading rate changes was found for the quadriceps. In addition, the input frequency was shown to approach the vibration frequency of the quadriceps. This evidence supports the proposed paradigm that muscle activity is tuned to impact force characteristics to control the soft-tissue vibrations.     

Effects of an individualized soccer match simulation on vertical stiffness and impedance

An observed relationship between soccer match duration and injury has led to research examining the changes in lower extremity mechanics and performance with fatiguing exercise. Because many fatigue protocols are designed to result in substantial muscular deficits, they may not reflect the fatigue associated with sport-specific demands that have been associated with the increasing incidence of injury as the match progresses. Thus, the aim of this study was to systematically analyze the progressive changes in lower extremity mechanics and performance during an individualized exercise protocol designed to simulate a 90-minute soccer match. Previous match analysis data were used to systematically develop a simulated soccer match exercise protocol that was individualized to the participant's fitness level. Twenty-four National Collegiate Athletic Association Division I soccer players (12 men, 12 women) participated in 2 testing sessions. In the first session, the participants completed the Yo-Yo Intermittent Recovery Test Level 1 to assess their fitness level and determine the 5 submaximal running intensities for their soccer match simulation. In the second test session, progressive changes in the rating of perceived exertion (RPE), lower extremity performance (vertical jump height, sprint speed, and cutting speed), and movement mechanics (jumping vertical stiffness and terminal landing impedance) were measured during the soccer match simulation. The average match simulation running distance was 10,165 ± 1,001 m, consistent with soccer match analysis research. Time-related increases in RPE, and decrements in sprinting, and cutting speed were observed, suggesting that fatigue increased as the simulation progressed. However, there were no time-related decreases in vertical jump height, changes in lower extremity vertical stiffness in jumping, or vertical impedance during landing. Secondary analyses indicated that the coordinative changes responsible for the maintenance of stiffness and impedance differed between the dominant and nondominant limbs. Despite an increase in RPE to near exhaustive levels, and decrements in sprint and cutting performance, the participants were able to maintain jump performance and movement mechanics. Interestingly, the coordinative changes that allowed for the maintenance of vertical stiffness and impedance varied between limbs. Thus, suggesting that unilateral training for performance and injury prevention in soccer-specific populations should be considered.     

The kinetics of lactate production and removal during whole-body exercise

Background

Based on a literature review, the current study aimed to construct mathematical models of lactate production and removal in both muscles and blood during steady state and at varying intensities during whole-body exercise. In order to experimentally test the models in dynamic situations, a cross-country skier performed laboratory tests while treadmill roller skiing, from where work rate, aerobic power and blood lactate concentration were measured. A two-compartment simulation model for blood lactate production and removal was constructed.

Results

The simulated and experimental data differed less than 0.5 mmol/L both during steady state and varying sub-maximal intensities. However, the simulation model for lactate removal after high exercise intensities seems to require further examination.

Conclusions

Overall, the simulation models of lactate production and removal provide useful insight into the parameters that affect blood lactate response, and specifically how blood lactate concentration during practical training and testing in dynamical situations should be interpreted.     

Impact severity in self-initiated sits and falls associates with center-of-gravity excursion during descent

Although the energy available during a fall from standing greatly exceeds that required to produce hip fracture, this occurs in only about 2% of falls in the elderly. This is thought to be due in part to one's ability to reduce the vertical impact velocity (nu(nu)) and kinetic energy (KE(nu)) of the body through energy absorption in the lower extremity muscles during descent. The present study tested the hypothesis that the magnitude and percent attenuation in nu(nu) and KE(nu) associate with the horizontal and vertical excursion of the body's center-of-gravity during descent. Measures were acquired of whole-body kinematics and lower extremity kinetics as young subjects underwent backward descents involving vertical drops of either thigh length (SIT) or lower extremity length (FALL), and horizontal pelvis excursions of either 33 or 66% of lower extremity length. In all trials, subjects attempted to "land as softly as possible." While attenuation in nu(nu) and KE(nu) (which averaged 62 and 92% respectively), did not associate with trial type, raw magnitudes of these parameters did, with nu(nu) averaging 2-fold greater, and KE(nu) averaging 6-fold greater, in 66% FALL than in 33% SIT or 66% SIT trials. This was due to a rapid increase in downward velocity accompanying the final stage of descent in 66% SIT and 66% FALL trials, which coincided with the knee moving posterior to the ankle. Accordingly, severe impacts likely accompany not only large fall heights, but also falls where the feet are thrown rapidly forward, as during a backward slip.     

Gender and foot orthotic device effect on frontal plane hip motion during landing from a vertical jump

Excessive hip motion has been linked to lower extremity pathology. Foot orthoses are commonly used to control motion within lower extremity joints when lower extremity pathology and dysfunction are present. Few studies have investigated the effect of foot orthoses on hip angular kinematics during functional activities. Eighteen females and 18 males performed a vertical jump with and without a prefabricated foot orthoses to determine the biomechanical effect of foot orthoses on hip kinematics when landing from a jump. Data collection included three-dimensional motion analysis of the lower extremity. Paired t tests were performed to determine if differences existed within genders with and without foot orthoses. At the hip joint, there was significantly less hip adduction motion in the foot orthoses condition as compared with the no foot orthoses condition in females (p < .05). There were no differences between foot orthoses conditions in males. Females appear to have a different proximal response to foot orthoses when landing from a forward jump than males.     

A Comparison of Frontal Theta Activity During Shooting among Biathletes and Cross-Country Skiers before and after Vigorous Exercise

Background

Previous studies using electroencephalography (EEG) to monitor brain activity have linked higher frontal theta activity to more focused attention and superior performance in goal-directed precision tasks. In biathlon, shooting performance requires focused attention after high-intensity cross-country skiing.

Purpose

To compare biathletes (serving as experts) and cross-country skiers (novices) and examine the effect of vigorous exercise on frontal theta activity during shooting.

Methods

EEG frontal theta (4–7 Hz) activity was compared between nine biathletes and eight cross-country skiers at comparable skiing performance levels who fired 100 shots on a 5-m indoor shooting range in quiescent condition followed by 20 shots after each of five 6-min high-intensity roller skiing sessions in the skating technique on a treadmill.

Results

Biathletes hit 80±14% and 81±10% before and after the roller skiing sessions, respectively. For the cross-country skiers these values were significantly lower than for the biathletes and amounted to 39±13% and 44±11% (p<0.01). Biathletes had on average 6% higher frontal theta activity during shooting as compared to cross-country skiers (F1,15 = 4.82, p = 0.044), but no significant effect of vigorous exercise on frontal theta activity in either of the two groups were found (F1,15 = 0.14, p = 0.72).

Conclusions

Biathletes had significantly higher frontal theta activity than cross-country skiers during shooting, indicating higher focused attention in biathletes. Vigorous exercise did not decrease shooting performance or frontal theta activity during shooting in biathletes and cross-country skiers.     

Differential specific mechanical energy as a quality parameter in racing alpine skiing

An important question in alpine skiing is how to determine characteristics of well-performed ski turns, an issue that has become more crucial with the arrival of new carving skis. This article introduces a new method for estimating the quality of skiing at each point of observation based on mechanical energy behavior that can be measured using established motion analysis techniques. It can be used for single or multiple-skier analyses for evaluation of skiing technique as well as racing tactics. An illustration of its use is shown by analyzing 16 top-level racers using a 3-D kinematical system and video recorded during an alpine ski world cup race. Based on energy behavior of several racers, it is demonstrated that the most direct line with shortest radius of turn is not necessarily the most effective strategy in contrast to what some coaches believe.     

Effect of Bending Strain on the Torsion Elastic Constant of DNA

The torsion constants of both circular and linear forms of the same 181 bp DNA were investigated by time-resolved fluorescence polarization anisotropy (FPA) of intercalated ethidium. The ratio of intrinsic ethidium binding constants of the circular and linear species was determined from the relative fluorescence intensities of intercalated and non-intercalated dye in each case. Possible changes in secondary structure were also probed by circular dichroism (CD) spectroscopy. Upon circularization, the torsion constant increased by a factor of 1.42, the intrinsic binding constant for ethidium increased by about fourfold, and the CD spectrum underwent a significant change. These effects are attributed to an altered secondary structure induced by the bending strain. Quantitative agreement between torsion constants obtained from the present FPA studies and previous topoisomer distribution measurements on circular DNAs containing 205 to 217 bp removes a long-standing apparent discrepancy between those two methods. After storage at 4°C for eight months, the torsion constant of the circular DNA increased by about 1.25-fold, whereas that of the linear DNA remained unchanged. For these aged circles, both the torsion constant and intrinsic binding constant ratio lie close to the corresponding values obtained previously for a 247 bp DNA by analyzing topoisomer distributions created in the presence of various amounts of ethidium. The available evidence strongly implies that torsion constants measured for small circular DNAs with less than 250 bp are specific to the altered secondary structure(s) therein, and are not applicable to linear and much larger circular DNAs with lower mean bending strains.     

理论雪期和滑雪气候适宜度评价——以长白山滑雪场为例

为科学分析雪资源气候属性,定量评价滑雪运动气候适宜度概况,本研究基于天气学原理,从气候角度设定了理论雪期概念;设定与滑雪运动密切相关的气温、风速、雪期降雪量3个指标的不同适宜度等级阈值,对各指标进行归一化处理并设计其转换函数;运用灰色关联度理论,结合欧氏距离法,构建滑雪气候适宜度指数评价模型,并以长白山滑雪场为例进行评价。结果表明: 长白山地区雪资源丰富,1981—2018年,理论雪期内的平均降雪量为64.6 mm;气候变暖背景下,平均雪期日数及降雪量随年代呈略有减少趋势,雪期开始时间随年代变化呈现延后趋势,结束时间呈提前趋势,且前冬(当年雪期开始至12月底)雪期日数明显少于后冬(次年1月初至雪期结束)雪期日数;长白山滑雪场雪期内滑雪气候适宜性高,气温、风速和降雪条件的最适宜和较适宜日数累计分别占91.9%、91.8%和94.6%;滑雪综合气候适宜度日数累计占比达99.7%,绝大多数时间适宜滑雪运动的开展。理论雪期概念的提出弥补了因初、终雪气象观测资料缺乏对雪资源研究等造成的困扰;滑雪运动气候适宜度评价模型可为滑雪场地开发和经营提供管理决策,为滑雪爱好者提供出行的科学支撑。     

改良曲张静脉点式剥除术治疗中老年下肢静脉曲张的临床疗效

目的:探究改良曲张静脉点式剥除术在治疗中老年下肢静脉曲张的临床疗效。方法:收集我院已确诊为下肢静脉曲张的中老年患者37例,分成实验组与对照组。对照组18例行传统曲张静脉点式剥除术,实验组19例行改良曲张静脉点式剥除术。对比两组患者手术后的下肢静脉曲张的治疗效果。结果:实验组有效率(94.7%)显著高于对照组(72.2%),差异具有统计学意义(P0.05);与对照组相比,实验组患者手术时间较短、术中出血量较少、下床活动时间较早,术后并发症总治愈率较高,复发率、术后并发症发生率较低,其差异均有统计学意义(P0.05)。结论:采用改良曲张静脉点式剥除术治疗中老年下肢静脉曲张的患者能够更彻底的剥除曲张额静脉,有效的改善患肢症状,明显降低复发率。     

Influence of central and extremity circumferences on all-cause mortality in men and women

For a given level of adiposity, greater lower body circumferences appear to exert a protective effect on several disease outcomes including cardiovascular disease and diabetes; however, the independent associations between extremity circumferences and mortality have not been widely investigated. The purpose of this study was to determine the independent and shared influences of upper- and lower-body circumferences on the risk of mortality in a population-based sample of adults. The sample included 10,638 adults 20-69 years of age (5,012 men; 5,626 women) from the nationally representative 1981 Canada Fitness Survey (CFS), who were monitored for over 12 years for mortality. BMI was calculated from measured height and weight. Waist, hip, thigh, calf, and upper arm circumferences were measured using a flexible, nonelastic anthropometric tape. Sex-specific proportional hazards regression models were used to evaluate the relationship between standardized values (Z-scores) of extremity circumference measures, waist circumference (WC) and mortality. Age, smoking status, alcohol consumption, and leisure-time physical activity were collected by questionnaire and were included as covariates. During 131,563 person-years of follow-up, there were 340 deaths in men and 231 in women. After mutual adjustment, WC was positively associated with mortality whereas arm, thigh, and calf circumferences were significantly protective in men, and arm and thigh circumferences were protective in women. In conclusion, waist and extremity circumferences appear to have opposite, independent effects on mortality in this sample of Canadians. Independent of BMI and WC, men and women with larger extremity circumferences had a lower risk of mortality.     

Training effects of cross-country skiing and running on maximal aerobic cycle performance and on blood lipids

Two experiments were carried out to compare the cardiorespiratory and metabolic effects of cross-country skiing and running training during two successive winters. Forty-year-old men were randomly assigned into skiing (n = 15 in study 1, n = 16 in study 2), running (n = 16 in study 1 and n = 16 in study 2) and control (n = 17 in study 1 and n = 16 in study 2) groups. Three subjects dropped out of the programme. The training lasted 9-10 weeks with 40-min exercise sessions three times each week. The training intensity was controlled at 75%-85% of the maximal oxygen consumption (VO2max) using portable heart rate metres and the mean heart rate was 156-157 beats.min-1 in the training groups. In the pooled data of the two studies the mean increase in the VO2max (in ml.min-1.kg-1) on a cycle ergometer was 17% for the skiing group, 13% for the running group and 2% for the control group. The increase in VO2max was highly significant in the combined exercise group compared to the control group but did not differ significantly between the skiing and running groups. The fasting serum concentrations of lipoproteins and insulin did not change significantly in any of the groups. These results suggested that training by cross-country skiing and running of the same duration and intensity at each session for 9-10 weeks improved equally the cardiorespiratory fitness of untrained middle-aged men.     

Measurement of strength and loading variables on the knee during Alpine skiing

The study focusses on the prevention of knee injuries during snow skiing. In order to develop a technology of knee injury prevention, both the strength and loading on the knee during skiing activity must be known. This paper reports measurements of variables influencing both knee strength and loading of the joint. The strength variables measured included the degree of activity in six muscles crossing the knee, the knee flexion angle, and the axial load (i.e. weight bearing) transmitted to the knee. Transducers included surface electrodes to monitor electromyogram signals indicating the degree of muscle activity and a goniometer to measure both hip and knee flexion angles. The complete loading on the knee was derived from a dynamometer which measured the six load components at the boot-dynamometer interface. The transducer data were acquired and stored by a compact, battery powered digital data acquisition-controller system. Three male subjects of similar physical size (nominal was 1.8 m and 75 kg) and skiing ability (advanced intermediate to expert) were tested under similar conditions. Each subject skied a total of four slalom runs--one snowplow and three parallel. The total time of each test was 21 s. Example data plots from different types of runs are presented and discussed. Based on observations from the data, necessary performance features for ski bindings offering improved protection from knee ligamentous injuries are defined.     

Control of dynamic foot-ground interactions in male and female soccer athletes: Females exhibit reduced dexterity and higher limb stiffness during landing

Controlling dynamic interactions between the lower limb and ground is important for skilled locomotion and may influence injury risk in athletes. It is well known that female athletes sustain anterior cruciate ligament (ACL) tears at higher rates than male athletes, and exhibit lower extremity biomechanics thought to increase injury risk during sport maneuvers. The purpose of this study was to examine whether lower extremity dexterity (LED) – the ability to dynamically control endpoint force magnitude and direction as quantified by compressing an unstable spring with the lower limb at submaximal forces – is a potential contributing factor to the “at-risk” movement behavior exhibited by female athletes. We tested this hypothesis by comparing LED-test performance and single-limb drop jump biomechanics between 14 female and 14 male high school soccer players. We found that female athletes exhibited reduced LED-test performance (p=0.001) and higher limb stiffness during landing (p=0.008) calculated on average within 51 ms of foot contact. Females also exhibited higher coactivation at the ankle (p=0.001) and knee (p=0.02) before landing. No sex differences in sagittal plane joint angles and center of mass velocity at foot contact were observed. Collectively, our results raise the possibility that the higher leg stiffness observed in females during landing is an anticipatory behavior due in part to reduced lower extremity dexterity. The reduced lower extremity dexterity and compensatory stiffening strategy may contribute to the heightened risk of ACL injury in this population.     

Agreement of measured and calculated muscle activity during highly dynamic movements modelled with a spherical knee joint

The inclusion of muscle forces into the analysis of joint contact forces has improved their accuracy. But it has not been validated if such force and activity calculations are valid during highly dynamic multidirectional movements. The purpose of this study was to validate calculated muscle activation of a lower extremity model with a spherical knee joint for running, sprinting and 90°-cutting. Kinematics, kinetics and lower limb muscle activation of ten participants were investigated in a 3D motion capture setup including EMG. A lower extremity rigid body model was used to calculate the activation of these muscles with an inverse dynamics approach and a cubic cost function. Correlation coefficients were calculated to compare measured and calculated activation. The results showed good correlation of the modelled and calculated data with a few exceptions. The highest average correlations were found during walking (r = 0.81) and the lowest during cutting (r = 0.57). Tibialis anterior had the lowest average correlation (r = 0.33) over all movements while gastrocnemius medius had the highest correlation (r = 0.9). The implementation of a spherical knee joint increased the agreement between measured and modelled activation compared to studies using a hinge joint knee. Although some stabilizing muscles showed low correlations during dynamic movements, the investigated model calculates muscle activity sufficiently.