Differences between motion capture and video analysis systems in calculating knee angles in elite-standard race walking

Race walking is an event where the knee must be straightened from first contact with the ground until midstance. The aim of this study was to compare knee angle measurements between 2D videography and 3D optoelectronic systems. Passive retroreflective markers were placed on the right leg of 12 race walkers and 3D marker coordinate data captured (250 Hz), with 2D video data (100 Hz) recorded simultaneously. Knee angle data were first derived based on the markers’ coordinates, and separately by using a 3D model that also incorporated thigh and shank clusters; the video data were analysed using both automatic tracking and manual digitising, creating four conditions overall. Differences were calculated between conditions for stance (using root mean square values), and at discrete events. There were few differences between systems, although the 3D model produced larger angles at midstance than using automatic tracking and marker coordinates (by 3 – 6°, P < 0.05). These differences might have occurred because of how the 3D model locates the hip joint, and because of the addition of marker clusters. 2D videography gave similar results to the 3D model when using manual digitising, as it allowed for errors caused by skin movement to be corrected.     

New insight for activity intensity relativity,metabolic expenditure during object projection skill performance

This study examined the metabolic cost (METs) of performing object projection skills at three practice trial intervals (6, 12, and 30 seconds). Forty adults (female n = 20) aged 18–30 (M = 23.7 ± 2.9 years) completed three, nine-minute sessions of skill trials performed at 6, 12, and 30 second intervals. Participants performed kicking, throwing and striking trials in a blocked schedule with maximal effort. Average METs during each session were measured using a COSMED K4b2. A three (interval condition) X two (sex) ANOVA was conducted to examine differences in METs across interval conditions and by sex. Results indicated a main effect for interval condition (F(5,114) = 187.02, p < .001, η² = 0.76) with decreased interval times yielding significantly higher METs [30 sec = 3.45, 12 sec = 5.68, 6 sec = 8.21]. A main effect for sex (F(5, 114) = 35.39, p < .001, η² = 0.24) also was found with men demonstrating higher METs across all intervals. At a rate of only two trials/min, participants elicited moderate physical activity, with 12 and 6-second intervals exhibiting vigorous PA. Demonstrating MVPA during the performance of object projection skill performance has potential implications for PA interventions.     

Effectiveness of motor skill intervention varies based on implementation strategy

Background: Young children from disadvantaged settings often present delays in fundamental motor skills (FMS). Young children can improve their FMS delays through developmentally appropriate motor skill intervention programming. However, it is unclear which pedagogical strategy is most effective for novice and expert instructors.

Purpose: The purpose of this study was to examine the effects of a motor skill intervention delivered by expert and novice teachers via direct or indirect pedagogical strategy on the object control and locomotor skills of young children.

Participants and setting: Participants included children (N?=?109) aged 40–67 months (M_age?=?54 months, SD?=?7 months) enrolled in an early years center for children who are socioeconomically disadvantaged in the United States.

Data collection: Children participated in one of five instructional conditions (expert-led direct, expert-led indirect, novice-led direct, novice-led indirect, and control). Expert and preservice physical education teachers implemented the Successful Kinesthetic Instruction for Preschoolers (SKIP) motor skill program twice weekly for 6 weeks (360?min of instruction). Children in all experimental conditions (n?=?69) received ‘business as usual’ free play on nonintervention days. Children in the control condition (n?=?40) received the ‘business as usual’ free play 5 days weekly throughout the entirety of the intervention. Children completed the Test of Gross Motor Development-2 during the pretest and the posttest.

Data analysis: For object control and locomotor skills, we conducted two, separate, one-way ANOVAs at the pretest to determine condition differences. We then calculated two separate, five conditions × two times repeated-measures ANOVAs to determine the effects of SKIP on both object control and locomotor skills. Tukey post hoc analyses confirmed posttest differences among the conditions.

Findings: There were no significant differences among conditions at the pretest (locomotor, p?=?.347–.969; object control, p?=?.143–.918). For object control skills, there were significant main effects for time (F[1, 104]?=?83.92, p?.001, η²?=?.45) and condition (F[4, 104]?=?6.39, p?<?.001, η²?=?.20) as well as a significant time by condition interaction (F[4, 104]?=?22.36, p?<?.001, η²?=?.45). For locomotor skills, there was a significant main effect for time (F[1, 104]?=?41.25, p?<?.001, η²?=?.28) but not for condition (F[4, 104]?=?2.20 p?<?.074, η²?=?.08). There was a significant time by condition interaction (F[1, 104]?=?18.68, p?<?.001, η²?=?.42). Experts, regardless of strategy, showed significantly greater improvements (p?<?.001) than novice and control conditions for locomotor skills. For object control skills, experts (all conditions) and novice-direct demonstrated significantly (p?<?.001) greater gains than the control and novice-indirect conditions.

Conclusion: Young children from disadvantaged settings demonstrated developmental delays with FMS. Motor skill intervention was effective with remediating their delays. Novice teachers with limited physical education experience should begin teaching object control skills via direct instruction. Experts can choose either direct or indirect instructional strategies. Future research should investigate the implications of scaffolding locomotor skills and indirect pedagogical strategies for novice teachers.     

Time–motion analysis of elite field hockey,with special reference to repeated-sprint activity

Limited information exists about the movement patterns of field-hockey players, especially during elite competition. Time–motion analysis was used to document the movement patterns during an international field-hockey game. In addition, the movement patterns of repeated-sprint activity were investigated, as repeated-sprint ability is considered to be an important fitness component of team-sport performance. Fourteen members of the Australian men's field-hockey team (age 26±3 years, body mass 76.7±5.6?kg, [Vdot]O_2max 57.9±3.6?ml?·?kg^?1?·?min^?1; mean±s) were filmed during an international game and their movement patterns were analysed. The majority of the total player game time was spent in the low-intensity motions of walking, jogging and standing (46.5±8.1, 40.5±7.0 and 7.4±0.9%, respectively). In comparison, the proportions of time spent in striding and sprinting were 4.1±1.1 and 1.5±0.6%, respectively. Our criteria for ‘repeated-sprint’ activity (defined as a minimum of three sprints, with mean recovery duration between sprints of less than 21?s) was met on 17 occasions during the game (total for all players), with a mean 4±1 sprints per bout. On average, 95% of the recovery during the repeated-sprint bouts was of an active nature. In summary, the results suggest that the motion activities of an elite field-hockey competition are similar to those of elite soccer, rugby and Australian Rules football. In addition, the investigation of repeated-sprint activity during competition has provided additional information about the unique physiological demands of elite field-hockey performance.     

JROTC as a Substitute for PE: Really?

Purpose: Even though physical education (PE) is an evidence-based strategy for providing and promoting physical activity, alternative programs such as the Junior Reserve Officer Training Corps (JROTC) are commonly substituted for PE in many states. The purpose of this study was to compare student physical activity and lesson contexts during high school PE and JROTC sessions. Method: The System for Observing Fitness Instruction Time was used to assess PE and JROTC sessions (N = 38 each) in 4 high schools that provided both programs. Data were analyzed using t tests, negative binomial regression, and logistic regression. Results: Students engaged in significantly more moderate-to-vigorous physical activity during PE than during JROTC sessions and they were significantly less sedentary. Significant differences between the 2 program types were also found among lesson contexts. Conclusions: PE and JROTC provide substantially different content and contexts, and students in these programs engage in substantially different amounts of moderate-to-vigorous physical activity. Students in JROTC, and perhaps other alternative programs, are less likely to accrue health-supporting physical activity and engage in fewer opportunities to be physically fit and motorically skilled. Policies and practices for providing substitutions for PE should be carefully examined.     

Urban Minority Ninth-Grade Students' Health-Related Fitness Knowledge

The purpose of the study was to examine Hispanic and other minority ninth-grade students' health-related fitness (HRF) knowledge, using FitSmart, a standardized test for high school students. The test consisted of 50 weighted multiple choice items, measuring six subcontent components. Means and standard deviations of the overall scores and the subcontent scores were computed. The findings suggested that students demonstrated mastery of one subcontent component but failed to meet passing values for all other subcontents and overall HRF knowledge. Female students outscored their male counterparts, but there was no difference for ethnicity. More efforts are needed to ensure that Hispanic and other minority high school students master fundamental HRF knowledge.     

Analysis of lower limb internal kinetics and electromyography in elite race walking

Abstract

The aim of this study was to analyse lower limb joint moments, powers and electromyography patterns in elite race walking. Twenty international male and female race walkers performed at their competitive pace in a laboratory setting. The collection of ground reaction forces (1000 Hz) was synchronised with two-dimensional high-speed videography (100 Hz) and electromyography of seven lower limb muscles (1000 Hz). As well as measuring key performance variables such as speed and stride length, normalised joint moments and powers were calculated. The rule in race walking which requires the knee to be extended from initial contact to midstance effectively made the knee redundant during stance with regard to energy generation. Instead, the leg functioned as a rigid lever which affected the role of the hip and ankle joints. The main contributors to energy generation were the hip extensors during late swing and early stance, and the ankle plantarflexors during late stance. The restricted functioning of the knee during stance meant that the importance of the swing leg in contributing to forward momentum was increased. The knee flexors underwent a phase of great energy absorption during the swing phase and this could increase the risk of injury to the hamstring muscles.     

Effect of sand versus grass training surfaces during an 8-week pre-season conditioning programme in team sport athletes

Abstract

This study compared the use of sand and grass training surfaces throughout an 8-week conditioning programme in well-trained female team sport athletes (n = 24). Performance testing was conducted pre- and post-training and included measures of leg strength and balance, vertical jump, agility, 20 m speed, repeat speed (8 × 20 m every 20 s), as well as running economy and maximal oxygen consumption (VO_2max). Heart rate (HR), training load (rating of perceived exertion (RPE) × duration), movement patterns and perceptual measures were monitored throughout each training session. Participants completed 2 × 1 h conditioning sessions per week on sand (SAND) or grass (GRASS) surfaces, incorporating interval training, sprint and agility drills, and small-sided games. Results showed a significantly higher (P < 0.05) HR and training load in the SAND versus GRASS group throughout each week of training, plus some moderate effect sizes to suggest lower perceptual ratings of soreness and fatigue on SAND. Significantly greater (P < 0.05) improvements in VO_2max were measured for SAND compared to GRASS. These results suggest that substituting sand for grass training surfaces throughout an 8-week conditioning programme can significantly increase the relative exercise intensity and training load, subsequently leading to superior improvements in aerobic fitness.