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1.
Background:One-legged pedaling is of interest to elite cyclists and clinicians.However,muscular usage in 1-legged vs.2-legged pedaling is not fully understood.Thus,the study was aimed to examine changes in leg muscle activation patterns between 2-legged and 1-legged pedaling.Methods:Fifteen healthy young recreational cyclists performed both 1-legged and 2-legged pedaling trials at about 30 Watt per leg.Surface electromyography electrodes were placed on 10 major muscles of the left leg.Linear envelope electromyography data were integrated to quantify muscle activities for each crank cycle quadrant to evaluate muscle activation changes.Results:Overall,the prescribed constant power requirements led to reduced downstroke crank torque and extension-related muscle activities(vastus lateralis,vastus medialis,and soleus)in 1-legged pedaling.Flexion-related muscle activities(biceps femoris long head,semitendinosus,lateral gastrocnemius,medial gastrocnemius,tensor fasciae latae,and tibialis anterior)in the upstroke phase increased to compensate for the absence of contralateral leg crank torque.During the upstroke,simultaneous increases were seen in the hamstrings and uni-articular knee extensors,and in the ankle plantarflexors and dorsiflexors.At the top of the crank cycle,greater hip flexor activity stabilized the pelvis.Conclusion:The observed changes in muscle activities are due to a variety of changes in mechanical aspects of the pedaling motion when pedaling with only 1 leg,including altered crank torque patterns without the contralateral leg,reduced pelvis stability,and increased knee and ankle stiffness during the upstroke.  相似文献   

2.
Background:Eccentric exercise increases muscle fascicle lengths;however,the mechanisms behind this adaptation are still unknown.This study aimed to determine whether biceps femoris long head(BFlh)fascicle length increases in response to 3 weeks of eccentric exercise training are the result of an in-series addition of sarcomeres within the muscle fibers.Methods:Ten recreationally active participants(age=27±3 years;mass=70±14 kg;height=174±9 cm;mean±SD)completed 3 weeks of Nordic hamstring exercise(NHE)training on a custom exercise device that was instrumented with load cells.We collected in vivo sarcomere and muscle fascicle images of the BFlh in 2 regions(central and distal)by using microendoscopy and 3 dimension ultrasonography.We then estimated sarcomere length,sarcomere number,and fascicle length before and after the training intervention.Results:Eccentric knee flexion strength increased after the training(15%;p<0.001;ηp2=0.75).Further,we found a significant increase in fascicle length(21%;p<0.001;ηp2=0.81)and sarcomere length(17%;p<0.001;ηp2=0.90)in the distal but not in the central portion of the muscle.The estimated number of sarcomeres in series did not change in either region.Conclusion:Fascicle length adaptations appear to be heterogeneous in the BFlh in response to 3 weeks of NHE training.An increase in sarcomere length,rather than the addition of sarcomeres in series,appears to underlie increases in fascicle length in the distal region of the BFlh.The mechanism driving regional increases in fascicle and sarcomere length remains unknown,but we speculate that it may be driven by regional changes in the pas sive tension of muscle or connective tis sue adaptations.  相似文献   

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4.
Purpose:The purpose of this study was to compare knee biomechanics of the replaced limb to the non-replaced limb of total knee replacement(TKR)patients and healthy controls during walking on level ground and on decline surfaces of 5°,10°,and 15°.Methods:Twenty-five TKR patients and 10 healthy controls performed 5 walking trials on different decline slopes on a force platform and an instrumented ramp system.Two analyses of variance,2×2(limb×group)and 2×4(limb×decline slope),were used to examine selected biomechanics variables.Results:The replaced limb of TKR patients had lower peak loading-response and push-off knee extension moment than the non-replaced and the matched limb of healthy controls.No differences were found in loading-response and push-off knee internal abduction moments among replaced,non-replaced,and matched limb of healthy controls.The knee flexion range of motion,peak loading-response vertical ground reaction force,and peak knee extension moment increased across all slope comparisons between 0°and 15°in both the replaced and non-replaced limb of TKR patients.Conclusion:Downhill walking may not be appropriate to include in early stage rehabilitation exercise protocols for TKR patients.  相似文献   

5.
Background:Osteoarthritis is one of the leading causes of pain and disability worldwide,and a large percentage of patients with osteoarthritis are individuals who are also obese.In recent years,a series of animal models have demonstrated that obesity-inducing diets can result in synovial joint damage(both with and without the superimposition of trauma),which may be related to changes in percentage of body fat and a series of low-level systemic inflammatory mediators.Of note,there is a disparity between whether the dietary challenges commence at weaning,representing a weanling onset,or at skeletal maturity,representing an adult onset of obesity.We wished to evaluate the effect ofthe dietary exposure time and the age at which animals are exposed to a high-fat and high-sucrose(HFS) diet to determine whether these factors may result in disparate outcomes,as there is evidence suggesting that these factors result in differential metabolic disturbances.Based on dietary exposure time,we hypothesized that rats fed an HFS diet for 14 weeks from weaning(HFS Weanling) would demonstrate an increase in knee joint damage scores,whereas rats exposed to the HFS diet for 4 weeks,starting at 12 weeks of age(HFS Adult) and rats exposed to a standard chow diet(Chow)would not display an increase in knee joint damage scores.Methods:Male Sprague-Dawley rats were fed either an HFS diet for 14 weeks from weaning(HFS Weanling) or an HFS diet for 4 weeks,starting at 12 weeks of age(HFS Adult).At sacrifice,joints were scored using the modified Mankin Criteria,and serum was analyzed for a defined subset of inflammatory markers(Interleukin-6,leptin,monocyte chemoattractant protein-1,and tumor necrosis factorα).Results:When the HFS Weanling and HFS Adult groups were compared,both groups had a similar percent of body fat,although the HFS Weanling group had a significantly greater body mass than the HFS Adult group.The HFS Weanling and HFS Adult animals had a significant increase in body mass and percentage of body fat when compared to the Chow group.Although knee joint damage scores were low in all 3 groups,we found,contrary to our hypothesis,that the HFS Adult group had statistically significant greater knee joint damage scores than the Chow and HFS Weanling groups.Furthermore,we observed that the HFS Weanling group did not have significant differences in knee joint damage scores relative to the Chow group.Conclusion:These findings indicate that the HFS Weanling animals were better able to cope with the dietary challenge of an HFS diet than the HFS Adult group.Interestingly,when assessing various serum proinflammatory markers,no significant differences were detected between the HTS Adult and HFS Weanling groups.Although details regarding the mechanisms underlying an increase in knee joint damage scores in the HFS Adult group remain to be elucidated,these findings indicate that dietary exposure time maybe less important than the age at which an HFS diet is introduced.Moreover,increases in serum proinflammatory mediators do not appear to be directly linked to knee joint damage scores in the HFS Weanling group animals but may be partially responsible for the observed knee joint damage in the adults over the very short time of exposure to the HFS diet.  相似文献   

6.
读者俱乐部     
RELAYS General characteristics Relay comprises a number of legs each of which is covered by a different athlete.Though there are standard events,relays and relay legs can be of any distance and often the various team members.In track relays each runner carries a baton by hand while running and at the completion of his or her leg exchanges it with the next leg runner.In road or cross country relays batons,sashes. and even the touch of hands can be used for the ex- changes.  相似文献   

7.
In the 1950s and early 1960s,the American society took on an air of unprecedented material prosperity.However,the flourishing economy failed to provide people with the spiritual content they expected to come with it.The inanition in the spiritual world and the affluence in the material world created a sharp contrast which led to a growing sense of anxiety and dissatisfaction.As a result,"many Americans reacted to these developments with ambivalence,even hostility." (Brinkley 1999:1010) It was against this milieu that Jerome David Salinger examines his growth as a young middle class American in retrospect and started his literary career.  相似文献   

8.
TagedPIn February and March 2022,China will host the Beijing 2022 Olympic and Paralympic Winter Games.The vision for this landmark event promises a“joyful rendezvous upon pure ice and snow uniting the passion of hundreds of millions for winter sports”.1 Themes have been developed to create a positive environmental impact with new development for the northern region of the country and to promote winter sports and improve the health and well-being of the Chinese people.The key messages for the winter games include inspiring youth with the Olympic spirit and encouraging millions to embrace winter sports.Notably,the Chinese government aims to mobilize at least 300 million of its citizens to engage in winter sports as an outcome of hosting the Winter Olympic Games.  相似文献   

9.
Background:Obesity increases knee osteoarthritis(OA) risk through metabolic,inflammatory,and biomechanical factors,but how these systemic and local mediators interact to drive OA pathology is not well understood.We tested the effect of voluntary running exercise after chronic diet-induced obesity on knee OA-related cartilage and bone pathology in mice.We then used a correlation-based network analysis to identify systemic and local factors associated with early-stage knee OA phenotypes among the different diet and exercise groups.Methods:Male C57 BL/6 J mice were fed a defined control(10% kcal fat) or high fat(HF)(60% kcal fat) diet from 6 to 37 weeks of age.At 25 weeks,one-half of the mice from each diet group were housed in cages with running wheels for the remainder of the study.Histology,micro computed tomography,and magnetic resonance imaging were used to evaluate changes in joint tissue structure and OA pathology.These local variables were then compared to systemic metabolic(body mass,body fat,and glucose tolerance),inflammatory(serum adipokines and inflammatory mediators),and functional(mechanical tactile sensitivity and grip strength) outcomes using a correlation-based network analysis.Diet and exercise effects were evaluated by two-way analysis of variance.Results:An HF diet increased the infrapatellar fat pad size and posterior joint osteophytes,and wheel running primarily altered the subchondral cortical and trabecular bone.Neither HF diet nor exercise altered average knee cartilage OA scores compared to control groups.However,the coefficient of variation was≥25% for many outcomes,and some mice in both diet groups developed moderate OA(>33% maximum score).This supported using correlation-based network analyses to identify systemic and local factors associated with early-stage knee OA phenotypes.In wheel-running cohorts,an HF diet reduced the network size compared to the control diet group despite similar running distances,suggesting that diet-induced obesity dampens the effects of exercise on systemic and local OA-related factors.Each of the 4 diet and activity groups showed mostly unique networks of local and systemic factors correlated with early-stage knee OA.Conclusion:Despite minimal group-level effects of chronic diet-induced obesity and voluntary wheel running on knee OA pathology under the current test durations,diet and exercise substantially altered the relationships among systemic and local variables associated with early-stage knee OA.These results suggest that distinct pre-OA phenotypes may exist prior to the development of disease.  相似文献   

10.
Background In many sports,athletes with low body weight and/or low body fat content have a distinct advantage over their opponents.Such an advantage can easily turn into a noticeable disadvantage because low body weight and 'leanness' may also be associated with health problems.Anorexia Athletica(AA) is associated with leanness and thinness in female and male sports athletes despite the fact that these athletes are often very successful.High-competitive athletes often restrict their caloric intake and/or increase their energy expenditure to maintain a low body mass and/or a low amount of body fat.Several metabolic and endocrine disturbances are often the result of prolonged energy restriction.These disturbances can be detected by alterations in the hormonal profile(low levels of leptin,increased levels of ghrelin) and in changes in body composition.  相似文献   

11.
BackgroundDuring an experiment, a ski racer equipped with various measurement devices suffered an anterior cruciate ligament (ACL) rupture in his right knee. The aim of this study was to describe the underlying injury mechanism from a functional perspective.MethodsEight giant slalom turns (i.e., 4 left turns), followed by 1 left turn at which the ACL injury occurred, were recorded by 2 video cameras, electromyography of 4 relevant muscle groups, inertial measurement units to measure knee and hip angles, and pressure insoles to determine ground reaction forces.ResultsDue to a loss of balance, the ski racer began to slide sideways at the apex of a left turn. During sliding, his right (outside) leg was actively abducted upward without touching the ground. The ski racer then attempted to stand up again by dropping his leg back towards the snow surface. The end of this dropping was accompanied by a decrease in electromyographic activity in the knee stabilizing muscles. Once the inside edge of the outer ski caught the snow surface, a rapidly increasing peak force, knee flexion, and an aggressive sudden activation of the vastus medialis muscle were observed, while biceps femoris and rectus femoris further decreased their activation levels. This likely resulted in excessive anterior translation of the tibia relative to the femur, causing damage to the ACL.ConclusionOur example emphasizes that ski racers should not get up until they stop sliding. Remember: “When you''re down, stay down.”  相似文献   

12.
PurposeTo determine the effect of unanticipated mid-flight medial-lateral external perturbation of the upper or lower trunk on anterior cruciate ligament (ACL) loading variables during jump-landings.MethodsThirty-two participants performed double-leg vertical jump-landings while bilateral kinematics and kinetics were collected under 6 conditions (upper or lower trunk perturbation locations; no, left, or right perturbation directions). Two customized catapult apparatuses were created to apply pushing perturbation to participants near the maximal jump height.ResultsThe ball contacted participants near the center of mass for the lower-trunk conditions and approximately 23 cm above the center of mass for the upper-trunk conditions. Under upper-trunk perturbation, the contralateral leg demonstrated significantly smaller knee flexion angles at initial contact and greater peak knee abduction angles, peak vertical ground reaction forces, peak knee extension moments, and peak knee adduction moments compared to other legs among all conditions. Under lower-trunk perturbation, the contralateral leg showed significantly smaller knee flexion angles at initial contact and increased peak vertical ground reaction forces and peak knee extension moments compared to legs in the no-perturbation conditions.ConclusionMid-flight external trunk pushing perturbation increased ACL loading variables for the leg contralateral to the perturbation. The upper-trunk perturbation resulted in greater changes in ACL loading variables compared to the lower-trunk perturbation, likely due to trunk and ipsilateral leg rotation and more laterally located center of mass relative to the contralateral leg. These findings may help us understand the mechanisms of indirect-contact ACL injuries and develop jump-landing training strategies under mid-flight trunk perturbation to better prevent ACL injury.  相似文献   

13.
Bulge-disc type pressure sensors of diameter 6 mm were fitted as near as possible to the running edge of a modern carved ski. The pressure signals were sampled at 30 Hz during long turns on snow, synchronously with signals from a geomagnetic compass and a pressure pad in the ski boot. The pressure from the snow was found to be highly variable with a mean value of about 50 kPa and dynamic pressure spikes up to 300 kPa. With the outside leg, the snow contact width in the rear part of the ski was found to be slightly wider, on average, than for the front part, as expected for a carving turn. Correlation within the pressure sensor data showed that the rapid pressure fluctuations were probably not due to bumps or features on the snow; instead they were probably caused by many small-scale collapses of the snow structure as the ski passed.  相似文献   

14.
Skiing manufacturers depend on the development of new skis on trial and error cycles and extensive product testing. Simulation tools, such as the finite element method, might be able to reduce the number of required testing cycles. However, computer programs simulating a ski in the situation of a turn so far lack realistic ski–snow interaction models. The aim of this study was to (a) implement a finite element simulation of a ski in a carved turn with an experimentally validated ski–snow interaction model, and (b) comparison of the simulation results with instantaneous turn radii determined for an actual carved turn. A quasi-static approach was chosen in which the ski–snow interaction was implemented as a boundary condition on the running surface of the ski. A stepwise linear function was used to characterise the snow pressure resisting the penetration of the ski. In a carved turn the rear section of the ski interacts with the groove that forms in the snow. Two effects were incorporated in the simulation to model this situation: (a) the plasticity of the snow deformation, (b) the influence of the ski’s side-cut on the formation and shape of this groove. The simulation results agreed well with experiments characterising snow penetration. Implementation of the groove in the ski–snow interaction model allowed calculation of the instantaneous turn radii measured in actual turns, but also caused significant numerical instability. The simulation contributes to the understanding of the mechanical aspects of the ski–snow interaction in carved turns and can be used to evaluate new ski designs.  相似文献   

15.
The purpose of this study was to examine whether differences in construction between the compact ski, the racing ski and the soft ski influence the behavioural and electromuscular responses of the user. Eight qualified male ski instructors performed two 'shuss' trials and three different basic turns. Six muscles (M. biceps femoris, M. gastrocnemius lateralis and medialis, M. rectus femoris, M. vastus lateralis and M. tibialis anterior) were studied, using a conventional but portable electromyographic (EMG) registration with telemetric synchronization, active electrodes and a six-channel portable data recorder. Muscle contractions were continuously registered and visualized in raw EMG form and linear envelopes. The differences between the mean rectified EMG data of dynamic contractions while skiing and the mean rectified EMG data of the maximal voluntary contraction were used in the primary analysis of data, from which the participation levels of the muscles investigated could be calculated for each type of ski. Based on this comparison, differences between the effects on muscle activity of the three types of skis were unimportant. In a second phase, the normalized linear envelopes of all subjects were graphically superimposed and averaged. This was performed for each muscle, for each movement, for each leg and for each ski tested. The EMG data were considered in combination with anthropometric values, with snow characteristics and with the velocity of skiing. This study showed systematic differences between the use of the racing, soft and compact ski. On average the soft ski showed the lowest muscle activity patterns and thus the most economical muscular efforts for all muscles investigated and within all movements.  相似文献   

16.
The purpose of this study was to examine whether differences in construction between the compact ski, the racing ski and the soft ski influence the behavioural and electromuscular responses of the user. Eight qualified male ski instructors performed two ‘shuss’ trials and three different basic turns. Six muscles (M. biceps femoris, M. gastrocnemius lateralis and medialis, M. rectus femoris, M. vastus lateralis and M. tibialis anterior) were studied, using a conventional but portable electromyographic (EMG) registration with telemetric synchronization, active electrodes and a six‐channel portable data recorder. Muscle contractions were continuously registered and visualized in raw EMG form and linear envelopes. The differences between the mean rectified EMG data of dynamic contractions while skiing and the mean rectified EMG data of the maximal voluntary contraction were used in the primary analysis of data, from which the participation levels of the muscles investigated could be calculated for each type of ski. Based on this comparison, differences between the effects on muscle activity of the three types of skis were unimportant. In a second phase, the normalized linear envelopes of all subjects were graphically superimposed and averaged. This was performed for each muscle, for each movement, for each leg and for each ski tested. The EMG data were considered in combination with anthropometric values, with snow characteristics and with the velocity of skiing. This study showed systematic differences between the use of the racing, soft and compact ski. On average the soft ski showed the lowest muscle activity patterns and thus the most economical muscular efforts for all muscles investigated and within all movements.  相似文献   

17.
The purpose of the study was to evaluate whether using only the semitendinosus as a tripled short graft would affect the electromechanical delay (EMD) of the knee flexors. EMD was evaluated in volunteers (N = 15) after they had undergone surgery for anterior cruciate ligament (ACL) reconstruction where the semitendinosus tendon alone was used as a graft. The results were compared with the intact leg and healthy controls (N = 15). After warming up, each subject performed four maximally explosive isometric contractions on an isokinetic dynamometer. Torques were measured by the dynamometer, while the electrical activity of the semitendinosus and biceps femoris muscles was detected using surface electromyography. EMD was found to be significantly increased (p = 0.001) in patients who had undergone ACL reconstruction compared to the controls. On the contrary, no significant differences (p = 0.235) were found for the biceps femoris muscle between the two groups. Similar results were found when the study group was compared with the intact leg group (p = 0.027 for semitendinosus and p = 0.859 for biceps femoris). Harvesting the semitendinosus tendon increases the EMD for the semitendinosus muscle but does not influence the EMD outcomes for the biceps femoris muscle.  相似文献   

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19.
We compared selected kinematic variables for four different ski turn techniques performed by five experienced and five intermediate male skiers. The four ski turn techniques were the upstem turn, the downstem turn, the parallel turn and the parallel step turn. Each turn was divided into the initiation phase and the first and second steering phases. Most of the statistically significant differences (P < 0.05) between the two groups were found for the initiation phases of the four turns. Both the hip axis-hand axis angle and the edging angle of the uphill ski were significantly different between the two groups for the upstem turn at the beginning of the initiation phase. For the downstem turn, significant differences between the groups were found at the start of the initiation phase for the hip axis-hand axis angle, the shoulder axis-fall line angle, and the edging angle of the uphill ski. The standard deviation of the distance between the tips of the two skis over the second steering phase also differed significantly between the two groups. For the parallel step turn, significant differences were found at the start of the initiation phase for the edging angle of the downhill ski and the downhill ski to movement direction angle. Significant differences were also found for the edging angle of the downhill ski in the middle of the second steering phase and the shoulder axis to movement direction angle at the end of this phase. For the initiation phase of the parallel turn, significant differences were found for the timing of setting the ski pole, the uphill knee angle at the start of this phase and the range of the knee angle of the uphill leg from the start to the end of this phase. For this turn, significant differences between the two groups were also found for the edging angle of the downhill ski in the middle of the second steering phase and the shoulder axis to movement direction angle at the end of this phase. One of the reasons it was possible to identify a few significant differences only for the turns analysed, was the variability within the intermediate group: for most of the variables analysed, the standard deviation was much higher for the intermediate than for the experienced group.  相似文献   

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