Shelby A. Peel

Foot position during landing directly influences knee mechanics. Thus, the purpose of this study was to determine success in practicing, repeating, and transferring a desired foot progression angle (FPA) during landing, as well as changes in knee mechanics. Twenty females were randomly assigned to a control or verbal instruction group. On day 1, each group performed 40 drop landings. The verbal instruction group was instructed to “Land with 30 degrees of external rotation” before every trial. Feedback was provided on a terminal schedule in the form of knowledge of FPA error. On day 2, retention was assessed with 5 drop landings, while transfer was assessed during a 2-step stop-jump landing. Repeated-measures analyses of variance (2 × 4 [group × time]) were used to assess the influence of verbal instruction on knee mechanics. Participants who received verbal instruction exhibited increased FPA. They also demonstrated increased initial contact knee abduction during acquisition and retention. For all participants, initial contact knee flexion increased, while peak knee adduction moment decreased during acquisition. While the verbal instruction cue was effective in promoting an increase in FPA and reducing some ACL injury risk factors during practice and retention, this cue may only be effective to tasks similar to what was practiced.

Background: Much of the research conducted on tactical-style boots has evaluated the biomechanical effect of boots in brand-new condition; however, the extent to which changes due to wear influence lower-extremity biomechanics remains uninvestigated. The purpose of this study was to compare lower-extremity biomechanics with worn-in boots and running shoes during both walking and running. Methods: Lower-extremity biomechanical parameters were evaluated during walking and running in 12 individuals with previous tactical experience. Participants were asked to complete one 5 min bout of walking and running at a self-selected pace in both self-selected athletic shoes and their own worn-in standard-issue tactical boots while lower-extremity spatiotemporal, joint kinematic, kinetic, and ground reaction force data were collected. Differences between conditions were evaluated using the Wilcoxon signed-rank test. Results: Spatiotemporal measures of gait, as well as ankle and hip kinematics, were different between shoes and boots during walking. During running, no spatiotemporal differences existed. However, significant differences were found for the ankle, knee, and hip kinematics between shoe and boot conditions during both walking and running. Conclusions: The worn-in boots in our sample performed similarly to running shoes during both walking and running tasks. Though there were several biomechanical differences between boots and shoes during both tasks, small mean differences suggest that these differences may not be large enough to create substantive or relevant changes in performance. This information could aid in developing future tactical boot design strategies to help aid in lower-extremity injury as well as allowing for optimal performance when wearing boots.

Including an unanticipated stimulus has significant impacts on lower extremity biomechanics during dynamic movements. It is unknown how a live, human defender affects lower extremity biomechanics. The purpose of this study was thus to determine the effects of two types of unanticipated stimuli (visual stimulus; defensive opponent) on lower extremity kinematics and kinetics in males and females during 45° sidestepping trials. Eight males and eight females completed two unanticipated stimuli sidestepping conditions. Numeric visual analog scales for reaction difficulty and movement realism were collected and analysed using a 2 × 2 mixed-model ANOVA. Three-dimensional hip, knee, and ankle kinematics and kinetics were measured during the stance phase of the sidestep and analysed using statistical parametric mapping. Participants reported greater difficulty and less realistic movements with the visual stimulus. Unanticipated stimulus main effects were observed for knee abduction angle, and hip extension and adduction, and knee extension and adduction moments. Sex main effects were observed for hip flexion, hip abduction, and ankle dorsiflexion angles, as well as hip abduction, ankle plantarflexion and ankle eversion moments and vertical ground reaction forces. Participants responded differently to two unanticipated stimuli. Careful consideration should be used when determining the type of unanticipated stimulus used.

Box and jump landing tasks are commonly used to study lower extremity injury mechanisms, such as anterior cruciate ligament (ACL) injuries. Arm restriction during these tasks is typically determined via researcher preference. Therefore, the purpose of this study was to compare three-dimensional lower extremity kinematics and kinetics during bilateral box and jump landings, and to determine the effects of arm restriction. Twenty-eight participants (14 males, 14 females) completed three bilateral landings tasks: box landings with arms unrestricted (BLA), box landings with arms restricted against the trunk (BLNA) and jump landings (JL). Right leg joint kinematics and kinetics were collected and compared between landing tasks. No statistically significant differences were found between BLA and BLNA, therefore arm restriction did not appear to influence lower extremity variables during bilateral box landings. However, specific injury-related variables, such as peak knee adduction moment differed between box and jump landings (BLNA: 0.31 ± 0.3 Nm/(kg·m)); JL: 0.45 ± 0.3 Nm/(kg·m); p = 0.020). Our results suggest that based on study purpose, careful consideration is needed when determining what bilateral landing task to choose during data collection.

Understanding the effects of training in different footwear on sporting performance would be useful to coaches and athletes. Purpose: This study compared the effects of computerized agility training using 3 types of footwear on change-of-direction and balance performance in young adults. Method: Thirty recreationally active young adults (M_age = 22.8 ± 3.1 years; M_height = 1.71 ± 0.7 m; M_bodymass = 73.4 ± 10.3 kg) were randomly assigned to a 6-week computerized agility training intervention in 1 of 3 footwear groups (n = 10/group): barefoot, minimal footwear, or traditional shoes. Participants had no previous barefoot or minimal-footwear training experience. Dependent variables included change-of-direction test time to completion, Star Excursion Balance Test, and single-leg stability evaluation. Testing was performed at the start of the training program, after 2 weeks, after 4 weeks, and at the end of the training program. Results: No group or time interactions were found for any of the dependent variables. Time main effects were observed for the performance measures of change of direction, Star Excursion, and single-leg-with-eyes-open stability evaluation. Participants improved in all 3 tests as early as 2 weeks into the intervention, with improvements continuing through the entire 6-week intervention. Conclusions: The lack of interaction and footwear effects suggests that agility and balance improvements during foot agility training are independent of footwear in a recreationally active young-adult population. Computerized agility training improves change-of-direction and balance performance within 2 weeks of training implementation. Future studies should consider footwear training effects in different populations, including frail older adults and athletes.