Relationship between backpack load location, sex, anthropometric and body composition factors with postural sway in healthy young adults.

Objective: Evaluate the effect of backpack load location on postural sway and correlate sway path length (PL) to anthropometrics and body composition. Methods: Fifteen participants aged 18-25 stood on a force plate with backpack load located high (LH), low (LL) or without backpack (NL). Body composition and anthropometric variables were correlated to PL. Results: Load increased PL, 95% confidence ellipse, and mean velocity while it reduced mediolateral SampEn (p<0.05). Females had increased mean velocity and PL of sway (p<0.05). Larger phase angles correlated with reduced PL under NL. Taller individuals correlated with reduced PL under LL. Greater mass correlated with reduced PL under LH. Conclusions: Load carriage regardless of load location increased postural sway metrics except mediolateral SampEn. Females had greater PL and mean velocity compared to males. Select anthropometric and body composition variables correlated with postural sway under different load conditions.

Objectif: Évaluer l'effet de la position de la charge du sac à dos sur le balancement postural et corréler la longueur du chemin du balancement (PL) aux facteurs anthropométriques et à la composition corporelle. Méthodologie: Quinze participants âgés de 18 à 25 ans se sont tenus debout sur une plateforme biomécanique, la charge du sac à dos étant placée à un niveau élevé (LH), bas (LL) ou sans sac à dos (NL). La composition corporelle et les variables anthropométriques ont été corrélées à la PL. Résultats: La charge a augmenté la PL, l'ellipse de confiance à 95 % et la vitesse moyenne tout en réduisant la SampEn (entropie d'échantillon) médio-latérale (p<0,05). Les femmes avaient une vitesse moyenne et une PL de balancement plus élevées (p<0,05). Les angles de phase plus importants sont en corrélation avec une réduction de la PL sous NL. Les personnes plus grandes étaient en corrélation avec une réduction de la PL sous LL. Une masse plus importante est en corrélation avec une réduction de la PL sous LH. Conclusions: Le port de charge, quelle que soit la position de la charge, a augmenté les paramètres du balancement postural, à l'exception de la SampEn médio-latérale. Les femmes avaient une PL et une vitesse moyenne plus élevées que les hommes. Certaines variables anthropométriques et de composition corporelle sont en corrélation avec le balancement postural dans différentes conditions de charge.

The effect of posture on neck proprioception and head/neck stabilization in asymptomatic participants.

OBJECTIVE: We sought to determine the effect of different body postures on neck proprioception and head/neck stabilization. METHODS: Twelve healthy college students completed a head repositioning task and a 'head still' task while wearing a headpiece (helmet) with laser fixed on top during standing, kneeling, sitting, and sitting with stabilization. Video data of the laser dot coordinates on a projection screen were obtained to examine the accuracy of the two tasks. RESULTS: There was a significant effect of both posture and vision for both vertical and horizontal head movements during the head still task. Standing and kneeling generated more variable head movement than sitting with or without stabilization. Posture did not significantly affect head repositioning accuracy. CONCLUSION: For healthy young adults, clinicians and researchers need to be concerned with postural influences on tasks that involve head/cervical spine stabilization, but not head repositioning accuracy.

OBJECTIF: Nous avons cherché à déterminer l'effet de différentes postures corporelles sur la proprioception du cou et la stabilisation tête/cou. MÉTHODES: Douze étudiants en bonne santé de niveau collégial ont accompli une tâche de repositionnement de la tête et une tâche d'immobilisation de la tête tout en portant un casque avec un laser fixé sur le dessus pendant qu'ils étaient debout, à genoux, assis et assis en état stable. Des données vidéo des coordonnées des points laser sur un écran de projection ont été obtenues pour examiner la précision des deux tâches. RÉSULTATS: On a observé un effet significatif de la posture et de la vision pour les mouvements verticaux et horizontaux de la tête pendant l'immobilisation de la tête. Le fait de se tenir debout et de s'agenouiller a généré un mouvement de la tête plus variable que le fait de s'asseoir en étant ou non stable. La posture n'a pas eu d'effet significatif sur la précision du repositionnement de la tête. CONCLUSION: Pour les jeunes adultes en santé, les cliniciens et les chercheurs doivent se préoccuper des influences posturales pour les tâches qui font appel à une stabilisation de la tête et de la colonne cervicale, mais non de la précision du repositionnement de la tête.

Temporal more than spatial regulation of sway is important for posture in response to an ultra-compliant surface.

BACKGROUND AND AIM: Many people use balance training as a rehabilitation or habilitation modality. Although the time course of changes to temporal and spatial aspects of postural sway over the initial weeks of such training is as yet unclear. Particularly, we sought to explore the effects of training on sway during a dynamic task of stance on an ultra-compliant surface. Such a task provides different mechanical, and thus sensorimotor, constraints compared to stance on a solid surface. METHODS: Center of pressure (COP) was measured on an ultra-compliant surface atop a force plate at the start of each of 18 days of a 6-week balance training program. Range and standard deviation quantified amount of sway while velocity and Lyapunov exponent (LyE) quantify speed and rhythmicity of sway, respectively. RESULTS: Trend analysis indicated quadratic changes in COP range and standard deviation, with initial reductions followed by returns to initial values by the end of training. Linear reduction of movement velocity and LyE continued through the duration of the program. Reduced LyE indicates regular (self-similar) structure of the COP path. CONCLUSIONS: These results provide insight to the developing postural strategy necessary for maintaining upright stance within the dynamics created by interactions with an ultra-compliant surface. Participants showed sensitivity to surface properties, moving both more slowly and with a more regular movement pattern; suggesting that they were able to develop a more feed-forward approach to the maintenance of balance by exploiting task constraints.

Effects of plyometrics performed during warm-up on 20 and 40 m sprint performance.

BACKGROUND: Postactivation potentiation in the form of a plyometric during warm-ups have been shown to improve performance in some speed/power events. This study aimed to determine if a plyometric during warm up can increase sprint performance in a 20 and 40 m sprint. METHODS: In this study we measured sprint times of 10 male track and field athletes over distances of 20 and 40 m after warm-ups with and without a plyometric exercise. The subjects performed the sprints at the same time on 2 different days, once with the experimental treatment, a plyometric exercise in the form of a plate jump, and once without. Plate jumps were chosen as the plyometric treatment because they do not require special equipment or facilities. The plate used for the plate jumps had a mass of 11.2 kilograms, which was between 12.8-16.6% of each athlete's body mass. RESULTS: Statistical analysis showed a decrease in sprint time when a plyometric was performed during the warm-up for both 20 (t-test P<0.05) and 40 m sprints (t-test P<0.01). The effect sizes of the improvement for both the 20 and 40 m sprints were d=0.459 and d=0.405, respectively, which is considered a small to medium effect. CONCLUSIONS: These results indicate that including a plyometric exercise during warm-ups can improve sprint performance in collegiate aged male sprinters during short sprints.

The acute effects of static stretching on the sprint performance of collegiate men in the 60- and 100-m dash after a dynamic warm-up.

Previous research has shown that static stretching has an inhibitory effect on sprinting performances up to 50 m. The purpose of this study was to see what would happen to these effects at longer distances such as those seen in competition. This study used a within-subjects design to investigate the effects of passive static stretching vs. no stretching on the 60- and 100-m sprint performance of college track athletes after a dynamic warm-up. Eighteen male subjects completed both the static stretching and the no stretching conditions in counterbalanced order across 2 days of testing. On each day, all subjects first completed a generalized dynamic warm-up routine that included a self-paced 800-m run, followed by a series of dynamic movements, sprint, and hurdle drills. At the end of this generalized warm-up, athletes were assigned to either a static stretching or a no-stretching condition. They then immediately performed 2 100-m trials with timing gates set up at 20, 40, 60, and 100 m. Results revealed a significant slowing in performance with static stretching (p < 0.039) in the second 20 (20-40) m of the sprint trials. After the first 40 m, static stretching exhibited no additional inhibition of performance in a 100-m sprint. However, although there was no additional time loss, athletes never gained back the time that was originally lost in the first portion of the trials. Therefore, in strict terms of performance, it seems harmful to include static stretching in the warm-up protocol of collegiate male sprinters in distances up to 100 m.

Gender bias on the effects of instruction on kinematic and kinetic jump parameters of high-level athletes.

The purposes of this study were to examine gender differences during drop jumps, to evaluate the effect of a set of simple instructions on kinematic and kinetic parameters during a drop jump, and to determine if there are gender differences in the effects of instruction on those parameters. Twenty-five basketball players, 13 men and 12 women, performed drop jumps from a box (height 30.5 cm) after being asked to perform a land and jump movement as they normally would do when aiming at maximum jump height. The experimental group received a set of instructions designed to make them land softer. The measured parameters were impact force at landing, ground contact time, flight time, frontal plane knee angle, sagittal plane knee angle, and distance between the knees. When the groups were examined by gender, no differences in the parameters were seen in men after instruction, but in women the following significant differences were detected: an increase in contact time, a decrease in landing force, and a decrease in inward movement of the knees after landing. These data indicate that females respond differently to jumping/landing instructions.

Gender bias in jumping kinetics in National Collegiate Athletic Association Division I basketball players.

The purposes of this study are to examine gender differences in the contribution of the arm swing to jump height in men and women basketball players and to examine the role of upper-body strength in the contribution of arm swing to jump height. National Collegiate Athletic Association Division I basketball players (men n = 13, women n = 12) performed 4 jumping movements: squat jumps with hands on hips (SNA) and with arm swings (SA) and countermovement jumps with hands on hips and with arm swings (CMA). Differences were found between the jump heights of men and women. Use of the arms increased the jump height of men more than women. Compared with the SNA, the SA allowed an increase of 7 cm (23%) for men and 4 cm (17%) for women. The CMA allowed for an increase of 10 cm (30%) for men and 6 cm (24%) for women. General upper-body strength measures did not correlate strongly with the effect of arms on jumping, but peak power did. As in previous studies, peak power had a high correlation with jumping performance. These results show that the arm swing contributes significantly to jump performance in both men and women basketball players and that strength training for jumping should focus on power production and lifting exercises that are jump specific.

Gender bias in the effects of arms and countermovement on jumping performance.

The ability to jump high is considered important in a number of sports. It is commonly accepted that the use of the arms and a counter movement increase jump height. In some sport situations (e.g., volley ball block, basketball rebound), athletes may not be able to utilize a counter movement or arm swing. The purpose of this study is to examine gender differences in the contribution of the arm swing and counter movement to vertical jump height. Fifty college students, 25 men (age = 21.4 +/- 1.7 years, height = 182.2 +/- 8 cm, weight = 83.7 +/- 12.4 kg) and 25 women (age = 20.7 +/- 1.6 years, height = 166.7 +/- 6.3 cm, weight = 61.5 +/- 7.0 kg), performed 4 jumping movements: squat jumps with hands on hips (SNA), counter movement jump with hands on hips (CMNA), squat jump with arm swing (SA), and counter movement with arm swing (CMA). Significant differences were found between men's and women's performance, as well as between each type of jump within each gender. A mixed-model analysis of variance detected gender differences with respect to changes in the jumping movement. For both sexes the jumps in order from worst to best were SNA, CMNA, SA, and CMA. Peak power values for men were 4,057, 4,020, 4,644, and 4,747 W, respectively, for the 4 jumps. The female power values were 2,543, 2,445, 2,842, and 2,788 W, respectively, for the 4 jumps. Arms increased jump height more than a counter movement for both genders, with jump heights for men at 29.6, 31, 36, and 38 cm, respectively, and those of women 21, 22, 26, and 27 cm, respectively. Use of the arms was found to increase the jump height of the men significantly more than that of women. Changes in jumping movements affect men and women differently. The greater increase in jump height for the men when using the arm swing could be because of greater upper body strength of men compared with women. This could have applications to training and upper body strength and also to modeling of jumping movements.

The validation of a portable force plate for measuring force-time data during jumping and landing tasks.

The purpose of this study was to determine the reliability and validity of a portable force plate when analyzing jumping and landing tasks. Subjects performed 3 drop vertical jumps and 3 drop landings on both a standard strain gauge laboratory force plate and a portable force plate. In contrast to typical laboratory installed force plates, the portable 6-component force plate can be easily transported and used onsite at various training or data collection sites and incorporates Hall effect technology. The measured parameters included maximum force and time to maximum force for initial stance of the both tests, maximum takeoff force, and time to maximum takeoff force for the drop vertical jump. The Pearson correlation coefficients for the drop landing and the drop vertical jump for maximum force (r = 0.942, r = 0.940), time to maximum force (r = 0.891, r = 0.920) and for drop jump maximum jumping force (r = 0.971), and time to maximum takeoff force (r = 0.917) were all high and indicate that the force data collected by a resistor-type portable force plate provide similar measures to a standard strain-gauge laboratory force plate. Additionally, the within session reliability of the drop landing and the drop vertical jump measured by the portable force plate showed high interclass correlation coefficients for examined variables of 0.979 and 9.67 for maximum landing force and 0.917 and 0.920 for time to maximum landing force, respectively. The interclass correlation coefficients for the maximum takeoff force and time to maximum takeoff force during the drop vertical jump were 0.991 and 0.86. The results indicate the force and timing measurements from the portable force plate were both valid and reliable. Use of the portable force plate may facilitate methods of force measurement that can be applied out into the field and therefore a valuable tool for on site landing and jump force measurements in a variety of settings for large numbers of subjects.