Preferential quadriceps activation in female athletes with incremental increases in landing intensity

The purpose of this study was to identify alterations in preparatory muscle activation patterns across different drop heights in female athletes. Sixteen female high school volleyball players performed the drop vertical jump from three different drop heights. Surface electromyography of the quadriceps and hamstrings were collected during the movement trials. As the drop height increased, muscle activation of the quadriceps during preparatory phase also increased (p < .05). However, the hamstrings activation showed no similar increases relative to drop height. Female athletes appear to preferentially rely on increased quadriceps activation, without an increase in hamstrings activation, with increased plyometric intensity. The resultant decreased activation ratio of the hamstrings relative to quadriceps before landing may represent altered dynamic knee stability and may contribute to the increased risk of ACL injury in female athletes.     

Quadriceps and hamstrings prelanding myoelectric activity during landing from different heights among male and female athletes

ACL tear is a major concern among athletes, coaches and sports scientists. More than taking the athlete away from training and competition, ACL tear is a risk factor for early-onset of knee osteoarthritis, and, therefore addressing strategies to avoid such injury is pertinent not only for competitive athletes, but for all physically active subjects. Imbalances in the prelanding myoelectric activity of the hamstrings and quadriceps muscles have been linked to ACL injuries. We investigated the effect of landing from different heights on prelanding myoelectric activity of the hamstrings and quadriceps muscles in recreational athletes. Thirty recreational athletes (15 male and 15 female) performed three bilateral drop jumps from two different heights; 20 cm and 40 cm while myoelectric activity of the vastus medialis, rectus femoris, biceps femoris and medial hamstrings were collected. When increasing the height of drop landing tasks prelanding normalized myoelectric activity of the quadriceps was increased by 15–20% but no significant changes were found for the hamstrings. Female athletes exhibited higher activity of the medial hamstrings compared to their male counterparts. We concluded that increasing the height of drop landing tasks is associated with increased myoelectric activity of the quadriceps but not the hamstrings in recreational athletes. These differences in muscle activity may be related to increased risk for ACL injury when the height is increased. Female athletes demonstrated higher recruitment of the medial hamstrings.     

A training program to improve neuromuscular indices in female high school volleyball players

The purpose of this study was to determine if a sports-specific training program could improve neuromuscular indices in female high school volleyball players. We combined components from a previously published knee ligament injury prevention intervention program for jump and strength training with additional exercises and drills to improve speed, agility, overall strength, and aerobic conditioning. We hypothesized that this sports-specific training program would lead to significant improvements in neuromuscular indices in high school female volleyball players. Thirty-four athletes (age 14.5 years ± 1.0) participated in the supervised 6-week program, 3 d·wk(-1) for approximately 90-120 minutes per session. The program was conducted on the school's volleyball court and weight room facilities. The athletes underwent a video drop-jump test, multistage fitness test, vertical jump test, and sit-up test before and after training. A significant increase was found in the mean VO2max score (p < 0.001), where 73% of the athletes improved this score. A significant improvement was found in the sit-up test (p = 0.03) and in the vertical jump test (p = 0.05), where 68% of the athletes increased their scores. In the drop-jump video test, significant increases were found in both the mean absolute knee separation distance (p = 0.002) and in the mean normalized knee separation distance (p = 0.04), indicating improved lower limb alignment on landing. No athlete sustained an injury or developed an overuse syndrome during training. This program significantly improved lower limb alignment on a drop-jump test, abdominal strength, estimated maximal aerobic power, and vertical jump height and may be implemented in high school female volleyball programs.     

A training program to improve neuromuscular and performance indices in female high school basketball players

The purpose of this study was to determine if a sports-specific training program could improve neuromuscular and performance indices in female high school basketball players. We combined components from a published anterior cruciate ligament injury prevention program for jump and strength training with other exercises and drills to improve speed, agility, overall strength, and aerobic conditioning. We hypothesized that this sports-specific training program would lead to significant improvements in neuromuscular and performance indices in high school female basketball players. Fifty-seven female athletes aged 14-17 years participated in the supervised 6-week program, 3 d·wk(-1) for approximately 90-120 minutes per session. The program was conducted on the basketball court and in weight room facilities in high schools. The athletes underwent a video drop-jump test, multistage fitness test, vertical jump test, and an 18-m sprint test before and upon completion of the training program. All the subjects attended at least 14 training sessions. After training, a significant increase was found in the mean estimated VO2max (p < 0.001), with 89% of the athletes improving this score. In the drop-jump video test, significant increases were found in the mean absolute knee separation distance (p < 0.0001) and in the mean normalized knee separation distance (p < 0.0001), indicating a more neutral lower limb alignment on landing. A significant improvement was found in the vertical jump test (p < 0.0001); however, the effect size was small (0.09). No improvement was noted in the sprint test. This program significantly improved lower limb alignment on a drop-jump test and estimated maximal aerobic power and may be implemented preseason or off-season in high school female basketball players.     

Reciprocal coactivation patterns of the medial and lateral quadriceps and hamstrings during slow, medium and high speed isokinetic movements.

The effect of movement velocity and fatigue on the reciprocal coactivation of the quadriceps and hamstrings was investigated through analysis of the root mean square (RMS) and the median frequency (MDF) of surface electromyography for the vastus medialis (VM), vastus lateralis (VL), medial hamstrings (MH) and biceps femoris (BF). Fourteen subjects performed six continuous isokinetic knee extension and flexion movements at 60 degrees, 180 degrees and 300 degrees s(-1), and 30 continuous movements at 300 degrees s(-1) to examine muscular fatigue patterns. Statistical analyses revealed that the RMS activity of the VM displayed greater coactivation than the VL (P<0.01) and the BF displayed greater coactivation than the MH (P<0.0001). There was no effect of velocity on the coactivation levels of the VM, the VL, or the MH; however, there was an effect of velocity on the coactivation levels of the BF (P<0.0001). Relative to MDF activity, the MH shifted upward as velocity increased (P<0. 01) while the BF decreased between 180 and 300 degrees s(-1) (P<0. 01). Results of the muscular fatigue test indicated that the RMS activity of the VM showed a higher degree of coactivation than the VL (P<0.01) and the BF showed approximately three times the coactivation level of the MH (P<0.001). The MDF of the VL and MH shifted downward as the repetitions progressed (P<0.01) with no changes for the VM or for the BF. Results of this study suggest that during isokinetic testing, both the VM and BF have significantly greater reciprocal coactivation levels when compared to the VL and MH, respectively. In addition, these results suggest that motor unit recruitment patterns of the VM and VL and the MH and BF differ with regard to the effects of velocity and fatigue.     

Aerobic performance of female marathon and male ultramarathon athletes.

The aerobic performance of thirteen male ultramarathon and nine female marathon runners were studied in the laboratory and their results were related to their times in events ranging in distance from 5 km to 84.64 km. The mean maximal aerobic power output (VO2 max) of the men was 72.5 ml/kg . min compared with 58.2 ml/kg . min (p less than 0.001) in the women but the O2 cost (VO2) for a given speed or distance of running was the same in both sexes. The 5 km time of the male athletes was closely related to their VO2 max (r = -0.85) during uphill running but was independent of relative power output (%VO2 max). However, with increasing distance the association of VO2 max with male athletic performance diminished (but nevertheless remained significant even at 84.64 km), and the relationship between %VO2 max and time increased. Thus, using multiple regression analysis of the form: 42.2 km (marathon) time (h) = 7.445 - 0.0338 VO2 max (ml/kg . min) - 0.0303% VO2 max (r = 0.993) and 84.64 km (London-Brighton) time (h) = 16.998 - 0.0735 VO2 max (ml/kg . min) - 0.0844% VO2 max (r = 0.996) approximately 98% of the total variance of performance times could be accounted for in the marathon and ultramarathon events. This suggests that other factors such as footwear, clothing, and running technique (Costill, 1972) play a relatively minor role in this group of male distance runners. In the female athletes the intermediate times were not available and they did not compete beyond 42.2 km (marathon) distance but for this event a similar association though less in magnitude was found with VO2 max (r = -0.43) and %VO2 max (= -0.49). The male athletes were able to sustain 82% VO2 max (range 80--87%) in 42.2 km and 67% VO2 max (range 53--76%) in 84.64 km event. The comparable figure for the firls in the marathon was 79% VO2 max (ranges 68--86%). Our data suggests that success at the marathon and ultramarathon distances is crucially and (possibly) solely dependent on the development and utilisation of a large VO2 max.     

Neuromuscular functioning of athletes and non-athletes in the drop jump

In many sports vertical jumping is important. This study compared neuromuscular functioning of the lower extremity muscles together with some kinetic and kinematic parameters before and during ground contact in drop jumps from two heights [0.4 m (DJ40) and 0.8 m (DJ80)] in 7 highly trained triple-jumpers and 11 physically active controls. The triple-jumpers jumped 32% higher in DJ40 and 34% higher in DJ80, had shorter braking and total contact times, and greater average and peak vertical ground reaction forces than the controls. In both drop jumps in the electromyogram pre-activity of the vastus lateralis and gastrocnemius muscles started earlier in the jumpers than in the controls. For the control group the increase in dropping height was associated with a decrease in the propulsion force, and resulted in more extended knee and ankle angles at touch down and more flexed angles at the deepest position than for the jumpers. All angular displacements for DJ80 were larger than for DJ40 in the control group. The triple jumpers and control subjects differed with respect to their neuromuscular functioning in the drop jump exercise and they responded in a different way to the increase in dropping height. Accepted: 2 April 1998     

Effects of environmental cooling on force production in the quadriceps and hamstrings

The purpose of this study was to determine the effects of environmental cooling on force production in the quadriceps and hamstring muscles. Ten men (mean +/- SD: age = 21.4 +/- 2.2 years, height = 168.5 +/- 35.9 cm, body mass = 78.0 +/- 6.4 kg) participated in this study. Each subject completed 2 sets of 10 maximal effort repetitions on a Cybex II isokinetic dynamometer at 3.14 rad x s(-1). Between sets, subjects sat in environmental temperatures of 20, 15, 10, or 5 degrees C for 40 minutes. A significant decrease (p 相似文献   

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.     

Skeletal muscle enzymes and fiber composition in male and female track athletes.

Muscle samples were obtained from the gastrocnemius of 17 female and 23 male track athletes, 10 untrained women, and 11 untrained men. Portions of the specimen were analyzed for total phosphorylase, lactic dehydrogenase (LDH), and succinate dehydrogenase (SDH) activities. Sections of the muscle were stained for myosin adenosine triphosphatase, NADH2 tetrazolium reductase, and alpha-glycerophosphate dehydrogenase. Maximal oxygen uptake (VO2max) was measured on a treadmill for 23 of the volunteers (6 female athletes, 11 male athletes, 10 untrained women, and 6 untrained men). These measurements confirm earlier reports which suggest that the athlete's preference for strength, speed, and/or endurance events is in part a matter of genetic endowment. Aside from differences in fiber composition and enzymes among middle-distance runners, the only distinction between the sexes was the larger fiber areas of the male athletes. SDH activity was found to correlate 0.79 with VO2max, while muscle LDH appeared to be a function of muscle fiber composition. While sprint- and endurance-trained athletes are characterized by distinct fiber compositions and enzyme activities, participants in strength events (e.g., shot-put) have relatively low muscle enzyme activities and a variety of fiber compositions.     

The effects of plyometric vs. dynamic stabilization and balance training on power, balance, and landing force in female athletes

Neuromuscular training protocols that include both plyometrics and dynamic balance exercises can significantly improve biomechanics and neuromuscular performance and reduce anterior cruciate ligament injury risk in female athletes. The purpose of this study was to compare the effects of plyometrics (PLYO) versus dynamic stabilization and balance training (BAL) on power, balance, strength, and landing force in female athletes. Either PLYO or BAL were included as a component of a dynamic neuromuscular training regimen that reduced measures related to ACL injury and increased measures of performance. Nineteen high school female athletes participated in training 3 times a week for 7 weeks. The PLYO (n = 8) group did not receive any dynamic balance exercises and the BAL (n = 11) group did not receive any maximum effort jumps during training. Pretraining vs. posttraining measures of impact force and standard deviation of center of pressure (COP) were recorded during a single leg hop and hold. Subjects were also tested for training effects in strength (isokinetic and isoinertial) and power (vertical jump). The percent change from pretest to posttest in vertical ground reaction force was significantly different between the BAL and PLYO groups on the dominant side (p < 0.05). Both groups decreased their standard deviation of center of pressure (COP) during hop landings in the medial/lateral direction on their dominant side, which equalized pretested side to side differences. Both groups increased hamstrings strength and vertical jump. The results of this study suggest that both PLYO and BAL training are effective at increasing measures of neuromuscular power and control. A combination of PLYO and BAL training may further maximize the effectiveness of preseason training for female athletes.     

Kinematic analysis of hip and knee angles during landing after imagery in female athletes

ABSTRACT: Sarafrazi, S, Bt Abdulah, RT, and Amiri-Khorasani, M. Kinematics analysis of hip and knee angles during landing after imagery in female athletes. J Strength Cond Res 26(9): 2356-2363, 2012-In sport settings, imagery is regarded as one of the most popular and effective techniques to enhance the learning strategies and performance of skills. However, its effect on the correction of improper technique such as landing, which causes injury, is not clear. Therefore, the purpose of this study is to investigate the effect of imagery on knee and hip flexion angle during jump landing in women. The landing motions were captured from 40 female physical education students (height: 166.05 ± 7.52 cm; mass: 55.75 ± 9.23 kg; age: 20.45 ± 1.66 years) using a 3-dimensional technique at 60 Hz by 3 video cameras. There was a significant difference between no imagery (27.04 ± 2.40°) and imagery (22.98 ± 1.95°) on knee valgus angle, and also, there was a significant difference between no imagery (44.88 ± 13.46°) and imagery (62.35 ± 8.34°) on the knee flexion angle (p ≤ 0.001). There is, in addition, a significant difference between the effect of no imagery (28.60 ± 4.88°) and imagery (39.73 ± 7.29°) on hip flexion angle (p ≤ 0.001). It seems that imagery can be used to correct motions and movements. Based on this finding, we concluded that imagery, probably, can be used as a training strategy to change athletic motion; however, the authors suggest further investigation into the efficacy of imagery in the prevention of anterior cruciate ligament injury.     

Cortisol and androgen concentrations in female and male elite endurance athletes in relation to physical activity.

To evaluate the effect of variations in physical activity on selected hormone concentrations in male versus female athletes, fasting serum concentrations of cortisol (C), total-testosterone, free-testosterone, non sex hormone binding globulin (SHBG) bound testosterone, dehydroepiandrosterone, 4-androstene-3,17-dione and SHBG were studied. The tests were performed in nine male and seven female elite endurance athletes during the off-season (test 1), early in the competition season (test 2) and at the end of the competition season (test 3). The C concentration increased significantly during the competition season in women but not in men. Further, the mean C concentrations at test 3 as well as the mean level during the whole observation period (tests 1, 2, 3) were significantly higher in women than in men. No significant changes were found in androgen concentrations or androgen:cortisol ratios within the two groups. The differences between the sexes in C response may indicate different adaptive mechanisms to similar physical stress.     

Sociosexuality as predictor of sexual harassment and coercion in female and male high school students

Sexual harassment and coercion have mainly been considered from a sex difference perspective. While traditional social science theories have explained harassment as male dominance of females, the evolutionary perspective has suggested that sex differences in the desire for sex are a better explanation. This study attempts to address individual differences associated with harassment from an evolutionary perspective. Considering previous research that has found links between sociosexual orientation inventory (SOI) and harassment, we consider whether this association can be replicated in a large, representative sample of high school students (N=1199) from a highly egalitarian culture. Expanding the previous studies which mainly focused on male perpetrators and female victims, we also examine females and males as both perpetrators and as victims. We believe that unrestricted sociosexuality motivates people to test whether others are interested in short-term sexual relations in ways that sometimes might be defined as harassment. Furthermore, unrestricted individuals signal their sociosexual orientation, and while they do not desire all individuals that react to these signals with sexual advances, they attract much more sexual advances than individuals with restricted sociosexual orientations, especially from other unrestricted members of the opposite sex. This more or less unconscious signaling thus makes them exploitable, i.e., harassable. We find that SOI is a predictor for sexual harassment and coercion among high school students. The paper concludes that, as expected, unrestricted sociosexuality predicts being both a perpetrator and a victim of both same-sex and opposite-sex harassment.     

Study of the fatigue curve in quadriceps and hamstrings of soccer players during isokinetic endurance testing

Many studies have presented regression models of quadriceps (Q) muscle strength loss with fatigue development. Paradoxically, the hamstrings (H), which are the principal site of muscle injury in soccer players, have received little attention, and no regression model has been established. This study investigated strength loss in the Q and H to establish a regression model using the lowest number of flexions-extensions during isokinetic endurance testing. Twenty-four semiprofessional soccer players performed 50 flexion-extension movements at 180 degrees x s(-1) on an isokinetic dynamometer. The theoretical equations were calculated from the first 10, first 15, first 20, and first 25 contractions for each muscle group by several regression models (linear, quadratic, cubic). The linear model was the best fit to this exercise protocol to describe the strength loss in both muscle groups. The quadratic model was the best fit to predict the changes in the H/Q ratio. This study showed that a regression model can be established for both muscle groups. A minimum of 20 extensions and 15 flexions was needed to establish a linear model that represented strength loss in, respectively, Q and H. A minimum of 25 flexions-extensions was needed with the quadratic model to accurately determine the decrease in the H/Q ratio. Isokinetic endurance testing can be carried out with only 25 flexions-extensions. This reduction should facilitate the implementation of this protocol. Regular evaluation would contribute to the efforts to prevent muscle injury during competitive sports activity.     

Aromatization and the induction of male sexual behavior in male, female, and androgenized female hamsters

Eight weeks after gonadectomy male, female, and androgenized [10 μg testosterone propionate (TP), 24 hr after birth] female hamsters were given daily treatment with: 150 μg dihydrotestosterone (DHT), 5 μg estradiol benzoate (EB), 150 μg DHT + 5 μg EB, 150 μg DHT + 1 μg EB, 30 μg DHT + 5 μg EB, 30 μg DHT + 1 μg EB, or the oil vehicle. Treatment of castrated male hamsters with 5 μg EB fully restored mounting but relatively few of these animals intromitted and none ejaculated. Treatment with 150 μg DHT restored all components of male sexual behavior but only in a small proportion of the males. Combined treatment with EB and DHT restored mounts, intromissions, and ejaculations in the majority of the males. Although as little as 30 μg DHT + 1 μg EB restored the full complement of male behavior, the males which received 150 μg DHT + 5 μg EB or 150 μg DHT + 1 μg EB required fewer intromissions to achieve ejaculation than the males which received 30 μg DHT + either dose of EB. The response of the androgenized females was similar to that of the males except that the androgenized females had lower intromission rates and none ejaculated. Relatively few of the nonandrogenized females responded to EB and DHT treatment and those that did mounted only a few times each test. These results demonstrate that both EB and DHT can stimulate male sexual behavior in the hamster and that the sensitivity to EB and DHT for copulatory behavior is determined by early postnatal androgen exposure.     

Variability of a set of hemodynamic parameters in young female and male athletes and nonathletes

Regulation of hemodynamics in young subjects was studied via estimating the variability of circulatory parameters. Slow-wave hemodynamic parameters and heart rate variability were shown to be individual-specific.     

The effectiveness of resisted jump training on the VertiMax in high school athletes

Resisted jumping devices and resisted plyometric training have become more common in recent years. The effectiveness of such training has yet to be determined among high school athletes. Sixty-four high school athletes (50 boys and 14 girls) from a variety of sports were divided into 2 groups and participated in a training intervention that differed only by the use of the VertiMax jump trainer in 1 group. Lower-body power was tested before and after the intervention and compared statistically for differences between the groups. Athletes from both groups followed a periodized training program with resistance exercises performed 2 or 3 days per week, and sprint and plyometric training (i.e., training control group) or sprint, plyometric, and VertiMax training (i.e., VertiMax group) 1 or 2 days per week, for 12 total weeks. In addition to the traditional compound lower-body lifts and equated sprint work, the VertiMax group performed supplementary exercises on the VertiMax training apparatus. The average improvement in power observed in the training control group was 49.50 +/- 97.83 W, and the increase in power in the VertiMax group was 217.14 +/- 99.21 W. The differences in power after the test and improvements in power with training were found to differ between the groups (P < 0.05) and favored the VertiMax training group. Combined with previous research with college athletes, these data show the added effectiveness of resisted jump training on the VertiMax among athletes for the development of lower-body power.