Sex differences in kinetic and neuromuscular control during jumping and landing.

In the present study, we analysed the kinetic profile together with the lower limb EMG activation pattern during a countermovement jump and its respective landing phase in males and females. Twenty subjects (10 males and 10 females) took part in the study. One experimental session was conducted in order to record kinetic and electromyographic (EMG) parameters during a countermovement jump (CMJ) and the subsequent landing phase. During the CMJ, males recorded a higher (p<0.001) performance than females in terms of jump height and power production. Stiffness values were lower in males than females due to greater centre of mass displacement during the countermovement (p<0.01). According to the EMG activity, males demonstrated greater (p<0.05) activation during the concentric phase of the jump. However, females revealed a higher co-contraction ratio in the plantar flexors during the push-off phase. During landings males showed higher (p<0.01) peak ground reaction forces (Fpeak), greater (p<0.05) stiffness and a higher maximal displacement of the CoM (p<0.05) than females. EMG analysis revealed greater EMG activity in the tibialis anterior (p<0.05) and rectus femoris (p=0.05) muscles in males. Higher plantar flexor co-activation during landing has also been found in males. Our findings demonstrated different neuromuscular control in males and females during jumping and landing.

Changes in footprint with resistance exercise.

We aimed to describe the changes in footprint characteristics after 2 types of resistance training sessions performed at different intensities. 18 young subjects (8 men and 10 women) volunteered for the study. All of them performed 2 different resistance training sessions, one with light loads (LS) and the other with heavy loads (HS). Their footprint was recorded and analysed before and after exercise. Lengths, widths, and areas of the footprint (rearfoot, midfoot, and forefoot) were measured. Almost all the variables significantly increased after both sessions. The greatest changes were found in the midfoot (area, LS: 10.4%; HS: 8.1%, P<0.0005; width, LS: 7.5%, P=0.002, and HS: 8%, P<0.0005). However, there were no significant differences between post-exercise data from both sessions. The variable that showed the smallest changes was the foot length (LS: 0.3%, P=0.023; HS: -0.4%, P=0.549). A resistance training session led to increases in most of the dimensions of the footprint, regardless of the magnitude of the loads handled. The greatest changes were found in the midfoot, indicating that the foot was flatter after exercise, and the foot changed more in width than in length.

Muscle morphology and jump performance: gender and intermuscular variability.

AIM: The present study aimed 1) to investigate the gender differences in jump performance and muscle architecture between men and women; and 2) to determine whether the differences in jump performance could be attributed to gender differences in the muscle architecture of the leg extensor muscles. METHODS: Sixty-two subjects volunteered for the study (34 women and 28 men): 19 club-level volleyball players, 20 physical education students, and 23 sedentary individuals. They performed trials of countermovement jumps (CMJ) and the muscle architecture of the vastus lateralis (VL), gastrocnemius medialis (GM), and lateralis (GL) were analyzed at rest by ultrasonography. RESULTS: There were significant differences in jump performance between men and women (CMJ height: 0.388 + or - 0.056 m in men and 0.279 + or - 0.060 m in women, P<0.001). There were also significant gender differences in the VL muscle thickness, while the relative fascicle length was significantly different in the three muscles studied, with longer fascicles in the VL muscle in men and longer fascicles in the gastrocnemii in women. There were significant associations between the VL muscle size and jump performance (r=0.49-0.50, P<0.001), and non linear relationships between muscle size parameters and pennation angles (R(2)=0.67-0.77, P<0.001). CONCLUSIONS: These results confirm that there are gender differences in the muscle architecture of people with a wide physical activity background. The gender differences found in the VL muscle size partially explained the differences in jump performance.

Landing differences between men and women in a maximal vertical jump aptitude test.

AIM: The aim of this study was to analyze the gender differences in the vertical ground reaction forces and the position of the center of gravity during the landing phase of a maximal vertical jump aptitude test. METHODS: The push-off, flight and landing phases of the jumps of 291 males (age = 19.6+/-2.8 years) and 92 females (age = 19.2+/-2.6 years), applicants to a Spanish faculty of sports sciences, were analyzed with a force platform. RESULTS: The greatest differences between men and women were found in the jump performance (women = 25.6+/-3.5 cm; men = 35.5+/-4.5 cm) and second peak vertical force value of the landing phase (women = 5.89+/-2.06 times body weight; men = 7.51 +/-2.38 times body weight), the values being greater in the men's group (P < 0.001). Correlation coefficients showed that the women utilized a different landing pattern than the one utilized by the men. CONCLUSION: Contrary to the authors' expectations, women showed lower second peak vertical force values during the landing. Taking into account only a kinetic point of view, they would have a lower risk of injury during the landing movement of maximal jumps. The lower values in the peak force, the delay of the impact of the calcaneus and the longer path of the center of gravity during the landing phase found in the women's group were related to a landing technique that is different from that of men.

Kinematics of ankle taping after a training session.

This study aimed to test the effectiveness of ankle taping on the limitation of forced supination during a change of direction, as well as the losses of effectiveness after a 30-minute training session. Fifteen young men with no ankle injury volunteered for the study. The static and dynamic ranges of movement (ROM) were measured before and after a training session. The dynamic measurements were recorded using high-speed 3D photogrammetry. The differences between static and dynamic measures of ankle supination and plantar flexion were significant. The losses of effectiveness during supination and ankle plantar flexion restriction were 42.3 % and 47.6 %, respectively. Ankle taping was effective in restricting the maximal static ROMs before a training session, but the effectiveness decreased after 30 min of training. The present study shows the necessity of performing dynamic ROM analysis of sports techniques involved in the ankle sprain mechanism in order to determine the degree of tape restriction after a training session, because there were differences between static and dynamic ankle ROMs. The lack of effects on the restriction of the dynamic plantar flexion would bring into question the necessity of ankle taping in subjects without previous injuries.

Assessment of power output in jump tests for applicants to a sports sciences degree.

AIM: Our study aimed: 1) to describe the jump performance in a population of male applicants to a Faculty of Sports Sciences, 2) to apply different power equations from the literature to assess their accuracy, and 3) to develop a new regression equation from this population. METHODS: The push off phases of the counter-movement jumps (CMJ) on a force platform of 161 applicants (age: 19+/-2.9 years; weight: 70.4+/-8.3 kg) to a Spanish Faculty of Sports Sciences were recorded and subsequently analyzed. Their hands had to be placed on the hips and the knee angle during the counter movement was not controlled. Each subject had 2 trials to reach a minimum of 29 cm of jump height, and when 2 jumps were performed the best trial was analyzed. Multiple regression analysis was performed to develop a new regression equation. RESULTS: Mean jump height was 34.6+/-4.3 cm, peak vertical force 1 663.9+/-291.1 N and peak power 3524.4+/-562 W. All the equations underestimated power, from 74% (Lewis) to 8% (Sayers). However, there were high and significant correlations between peak power measured on the force platform, and those assessed by the equations. CONCLUSIONS: The results of the present study support the development of power equations for specific populations, to achieve more accurate assessments. The power equation from this study [Power = (62.5 x jump height (cm)) + (50.3 x body mass (kg)) 2184.7] can be used accurately in populations of male physical education students.

Maximal and explosive force production capacity and balance performance in men of different ages.

A group of 32 healthy men (M) divided into three different age groups, i.e. M20 years [mean 21 (SD 1); n = 12], M40 [mean 40 (SD 2); n = 10] and M70 [mean 71 (SD 5); n = 10] volunteered as subjects for examination of maximal and explosive force production of leg extensor muscles in both isometric and dynamic actions (squat jump, SJ and counter movement jump, CMJ, and standing long-jump, SLJ). The balance test was performed on a force platform in both isometric and dynamic actions. Maximal bilateral isometric force value in M70 was lower (P < 0.001) than in M40 and as much as 46% lower (P < 0.001) than that recorded in M20 (P < 0.001). The maximal rate of force development (RFD) on the force-time curve was in M70 lower (P < 0.001) than in M40 and as much as 64% lower than in M20. The heights in SJ and CMJ and the distance in SLJ in M70 were lower (P < 0.001) than in M40 and M20 (P < 0.001). In response to modifications of the visual surroundings the older subjects were 24%-47% (P < 0.05 and P < 0.001) slower in their response time in reaching the lit centre (TT) and remained 20%-34% (P < 0.001) less time inside the centre (TC) from the overall time of lighting than M40 and M20, respectively. In both older groups the individual values of isometric RFD correlated significantly (P < 0.05) with the individual balance values of TT and TC. The present results would suggest that the capacity for explosive force production declines drastically with increasing age, even more than maximal muscle strength. Aging may also lead to impaired balance with a decrease in event detection and speed of postural adjustments. The decreased ability to develop force rapidly in older people seems to be associated with a lower capacity for neuromuscular response in controlling postural sway.