John R. Harry

Analysis of gait symmetry during over-ground walking in children with autism spectrum disorder

Gait symmetry is utilized as an indicator of neurologic function. Healthy gait often exhibits minimal asymmetries, while pathological gait exhibits exaggerated asymmetries. The purpose of this study was to examine symmetry of mechanical gait parameters during over-ground walking in children with Autism Spectrum Disorder (ASD). Kinematic and kinetic data were obtained from 10 children (aged 5-12 years) with ASD. The Model Statistic procedure (α=0.05) was used to compare gait related parameters between limbs. Analysis revealed children with ASD exhibit significant lower extremity joint position and ground reaction force asymmetries throughout the gait cycle. The observed asymmetries were unique for each subject. These data do not support previous research relative to gait symmetry in children with ASD. Many individuals with ASD do not receive physical therapy interventions, however, precision medicine based interventions emphasizing lower extremity asymmetries may improve gait function and improve performance during activities of daily living.

Effects of Footwear Condition on Maximal Jumping Performance

Abstract Harry, JR, Paquette, MR, Caia, J, Townsend, RJ, Weiss, LW, and Schilling, BK. Effects of footwear condition on maximal jumping performance. J Strength Cond Res 29(6): 1657–1665, 2015—The purpose of this investigation was to examine the effects of footwear on kinetics and lower extremity electromyographic (EMG) activity during the vertical jump (VJ) and standing long jump. Fifteen men performed the 2 jump types in 3 footwear conditions: barefoot, minimal shoes, and cross-training shoes. Jump displacement and kinetic data were collected, along with EMG activity of the biceps femoris, medial gastrocnemius, peroneus longus, semitendinosus/semimembranosus, soleus (SOL), tibialis anterior, vastus lateralis, and vastus medialis. Subjective footwear performance and comfort were also assessed with a custom survey. No differences were found in jump displacement, peak ground reaction forces (GRF), countermovement and propulsive phase durations, vertical impulse, peak countermovement, or average propulsive EMG activity. Significant differences in peak propulsive root mean square EMG were found between barefoot and minimal shoes (p = 0.030) and minimal shoes and shod (p = 0.031) conditions for the SOL during the VJ, and for average countermovement EMG of the semitendinosus/semimembranosus during the VJ between barefoot and shod (p = 0.039). Moderate-to-large effect sizes (>0.59) were found between conditions for horizontal GRF, propulsive phase duration, average EMG amplitude, and duration of EMG activity during the countermovement. Participants reported higher comfort ratings when shod compared with barefoot and minimal shoes for both jumps. Participants also perceived better performance when shod compared with barefoot and minimal shoes for the VJ only. No acute differences in displacement were observed between barefoot, minimal shoes, and cross-trainer shoes during vertical and horizontal jumps. Some differences in muscle activation and timing seem to be present, and thus, training effects between footwear conditions should be examined. Footwear familiarization may prove beneficial, as acute increases in comfort seem unrelated to performance improvements.

A Comparative Evaluation of Gait between Children with Autism and Typically Developing Matched Controls

Anecdotal reports suggest children with autism spectrum disorder (ASD) ambulate differently than peers with typical development (TD). Little empirical evidence supports these reports. Children with ASD exhibit delayed motor skills, and it is important to determine whether or not motor movement deficits exist during walking. The purpose of the study was to perform a comprehensive lower-extremity gait analysis between children (aged 5–12 years) with ASD and age- and gender-matched-samples with TD. Gait parameters were normalized to 101 data points and the gait cycle was divided into seven sub-phases. The Model Statistic procedure was used to test for statistical significance between matched-pairs throughout the entire gait cycle for each parameter. When collapsed across all participants, children with ASD exhibited large numbers of significant differences (p < 0.05) throughout the gait cycle in hip, knee, and ankle joint positions as well as vertical and anterior/posterior ground reaction forces. Children with ASD exhibited unique differences throughout the gait cycle, which supports current literature on the heterogeneity of the disorder. The present work supports recent findings that motor movement differences may be a core symptom of ASD. Thus, individuals may benefit from therapeutic movement interventions that follow precision medicine guidelines by accounting for individual characteristics, given the unique movement differences observed.

Effects of Active Workstation Use on Walking Mechanics and Work Efficiency

Recently, the amount of time dedicated to sedentary work-related tasks has increased. Further, this trend toward decreased physical activity in the workplace is expected to increase. Active workstations such as treadmill desks provide health benefits; however, concerns for the ability to walk safely and work efficiency remain unclear. The purposes of this investigation were to: 1) compare kinematics of treadmill walking (TW) with kinematics of walking while performing computer mousing tasks (WC) using a treadmill desk, and 2) examine work efficiency in terms of the time to complete computer mousing tasks during WC compared to standing (SC). Trunk and lower-extremity kinematic data were obtained from 9 males (23.4 ± 4.2 yrs; 81.7 ± 16.4 kg; 176.3 ± 5.5 cm) and 7 females (23.0 ± 3.3 yrs; 58.4 ± 6.5 kg; 171.7 ± 9.0 cm) using a 10-camera motion capture system. Kinematic data were normalized to the gait cycle and were divided into sub-phases for analysis. Kinematic data of the first and last 10 WC strides were compared to identify shortterm kinematic adaptations (α=0.05). Neither computer task performance (p=0.071) nor walking velocity (p=0.089) was sacrificed during WC compared to SC and TW, respectively. Significant kinematic changes occurred in response to WC (p<0.05). Significant differences were identified between the first and last 10 WC strides (p<0.05), which revealed that some participants trended toward a return to normal gait as exposure to WC increased. Results suggest that active workstations do not diminish computing performance, and that walking safety is not sacrificed after initial exposure. We suggest gradual introduction to an active workstation, particularly if the computer task is challenging.

Aerial Rotation Effects on Vertical Jump Performance Among Highly Skilled Collegiate Soccer Players.

Abstract Barker, LA, Harry, JR, Dufek, JS, and Mercer, JA. Aerial rotation effects on vertical jump performance among highly skilled collegiate soccer players. J Strength Cond Res 31(4): 932–938, 2017—In soccer matches, jumps involving rotations occur when attempting to head the ball for a shot or pass from set pieces, such as corner kicks, goal kicks, and lob passes. However, the 3-dimensional ground reaction forces used to perform rotational jumping tasks are currently unknown. Therefore, the purpose of this study was to compare bilateral, 3-dimensional, and ground reaction forces of a standard countermovement jump (CMJ0) with those of a countermovement jump with a 180° rotation (CMJ180) among Division-1 soccer players. Twenty-four participants from the soccer team of the University of Nevada performed 3 trials of CMJ0 and CMJ180. Dependent variables included jump height, downward and upward phase times, vertical (Fz) peak force and net impulse relative to mass, and medial-lateral and anterior-posterior force couple values. Statistical significance was set a priori at &agr; = 0.05. CMJ180 reduced jump height, increased the anterior-posterior force couple in the downward and upward phases, and increased upward peak Fz (p ⩽ 0.05). All other variables were not significantly different between groups (p > 0.05). However, we did recognize that downward peak Fz trended lower in the CMJ0 condition (p = 0.059), and upward net impulse trended higher in the CMJ0 condition (p = 0.071). It was concluded that jump height was reduced during the rotational jumping task, and rotation occurred primarily via AP ground reaction forces through the entire countermovement jump. Coaches and athletes may consider additional rotational jumping in their training programs to mediate performance decrements during rotational jump tasks.

Vertical and Horizontal Impact Force Comparison During Jump Landings With and Without Rotation in Ncaa Division I Male Soccer Players

Abstract Harry, JR, Barker, LA, Mercer, JA, and Dufek, JS. Vertical and horizontal impact force comparison during jump landings with and without rotation in NCAA Division I male soccer players. J Strength Cond Res 31(7): 1780–1786, 2017—There is a wealth of research on impact force characteristics when landing from a jump. However, there are no data on impact forces during landing from a jump with an airborne rotation about the vertical axis. We examined impact force parameters in the vertical and horizontal axes during vertical jump (VJ) landings and VJ landings with a 180° rotation (VJR). Twenty-four Division I male soccer players performed 3 VJ and VJR landings on a dual-force platform system. Paired-samples t-tests (&agr; = 0.05) compared differences in the first (F1) and second (F2) peak vertical ground reaction forces, times to F1 (tF1), F2 (tF2), and the end of the impact phase, vertical impulse, and anterior-posterior and medial-lateral force couples. Effect sizes (ES; large >0.8) were computed to determine the magnitude of the differences. Lower jump height (41.60 ± 4.03 cm, VJ landings; 39.40 ± 4.05 cm, VJR landings; p = 0.002; ES = 0.39), greater F2 (55.71 ± 11.95 N·kg−1, VJ; 68.16 ± 14.82 N·kg−1; p < 0.001; ES = 0.94), faster tF2 (0.057 ± 0.012 seconds, VJ; 0.047 ± 0.011 seconds, VJR; p = 0.001; ES = 0.89), greater anterior-posterior (0.06 ± 0.03 N·s·kg−1, VJ; 0.56 ± 0.15 N·s·kg−1, VJR; p < 0.001; ES = 1.83) and medial-lateral force couples (0.29 ± 0.11 N·s·kg−1, VJ; 0.56 ± 0.14 N·s·kg−1, VJR; p < 0.001; ES = 1.46) occurred during VJR landings. No other differences were identified. This kinetic analysis determined that landing from a jump with 180° airborne rotation is different than landing from a jump without an airborne rotation. Male Division I soccer players could benefit from increasing the volume of VJR landings during training to address the differences in jump height and force parameters compared with VJ landings.

Relationships Between Countermovement Jump Ground Reaction Forces and Jump Height, Reactive Strength Index, and Jump Time

Abstract Barker, LA, Harry, JR, and Mercer, JA. Relationships between countermovement jump ground reaction forces and jump height, reactive strength index, and jump time. J Strength Cond Res 32(1): 248–254, 2018—The purpose of this study was to determine the relationship between ground reaction force (GRF) variables to jump height, jump time, and the reactive strength index (RSI). Twenty-six, Division-I, male, soccer players performed 3 maximum effort countermovement jumps (CMJs) on a dual-force platform system that measured 3-dimensional kinetic data. The trial producing peak jump height was used for analysis. Vertical GRF (Fz) variables were divided into unloading, eccentric, amortization, and concentric phases and correlated with jump height, RSI (RSI = jump height/jump time), and jump time (from start to takeoff). Significant correlations were observed between jump height and RSI, concentric kinetic energy, peak power, concentric work, and concentric displacement. Significant correlations were observed between RSI and jump time, peak power, unload Fz, eccentric work, eccentric rate of force development (RFD), amortization Fz, amortization time, second Fz peak, average concentric Fz, and concentric displacement. Significant correlations were observed between jump time and unload Fz, eccentric work, eccentric RFD, amortization Fz, amortization time, average concentric Fz, and concentric work. In conclusion, jump height correlated with variables derived from the concentric phase only (work, power, and displacement), whereas Fz variables from the unloading, eccentric, amortization, and concentric phases correlated highly with RSI and jump time. These observations demonstrate the importance of countermovement Fz characteristics for time-sensitive CMJ performance measures. Researchers and practitioners should include RSI and jump time with jump height to improve their assessment of jump performance.

Lower extremity joint stiffness during walking distinguishes children with and without autism

How children with Autism Spectrum Disorder (ASD) and peers with typical development (TD) modulate lower extremity stiffness during walking could identify a mechanism for gait differences between groups. We quantified differences in lower extremity joint stiffness and linear impulses, along the vertical and anterior/posterior axes during over-ground walking in children with ASD compared to age- and gender-matched children with TD. Nine age- and gender-matched pairs of children, aged 5-12 years, completed the current study. Joint stiffness and linear impulses were computed in four sub-phases of stance: loading response, mid-stance, terminal stance, and pre-swing. The Model Statistic technique (α = 0.05) was used to test for statistical significance between the matched-pairs for each variable and sub-phase. Furthermore, dependent t-tests (α = 0.05) were utilized, at the group level, to determine whether significant differences existed between sub-phases. Results indicate that children with ASD may exhibit greater stiffness in pre-swing, and thus, produce inefficient propulsive forces during walking. We attribute these differences to sensory processing dysfunction previously observed in children with ASD.

Performance Differences Among Skilled Soccer Players of Different Playing Positions During Vertical Jumping and Landing

Abstract Harry, JR, Barker, LA, James, CR, and Dufek, JS. Performance differences among skilled soccer players of different playing positions during vertical jumping and landing. J Strength Cond Res 32(2): 304–312, 2018—Both jumping and landing performance of skilled soccer players is diminished when task demands are increased. However, it is unclear if performance changes are specific to players of certain playing positions. Therefore, we assessed jumping and landing performance among skilled soccer players of different playing positions. Twenty-five National Collegiate Athletic Association (NCAA) Division 1 male soccer players (179.5 ± 7.8 cm, 75.5 ± 7.1 kg, 19.7 ± 1.2 years) performed maximum effort vertical jump landings (VJLs), whereas vertical ground reaction force (vGRF) data were obtained. Participants were stratified into goalkeeping (GK), defensive (DEF), midfield (MID), and attacking (ATT) group according to their primary playing position. One-way analyses of variance (&agr; = 0.05) and effect sizes (ESs; large ≥ 0.80) were used to compare differences among groups. The jumping phase variables evaluated were jump height, unloading and amortization vGRF magnitudes, eccentric rate of force development, and the reactive strength index. Landing phase variables included the peak vGRF magnitude, vGRF loading rate, vGRF attenuation rate, and landing time. No statistically significant differences were detected for any jumping or landing variable (p ≥ 0.05). However, a number of large magnitude differences were detected during landing after ES calculations. Specifically, greater peak vGRF magnitudes were detected in DEF vs. both MID (ES = 1.08) and ATT (ES = 0.93), a greater vGRF loading rate occurred in DEF vs. MID (ES = 0.93), and a greater vGRF attenuation rate occurred in DEF vs. both MID (ES = 1.00) and AT (ES = 0.80). It is concluded that highly skilled soccer players possess position-specific abilities with respect to the landing phase of VJL. Skilled soccer players might experience enhanced training outcomes after VJL training regimens tailored to the specific demands of their primary playing position.

Comparison of pre-contact joint kinematics and vertical impulse between vertical jump landings and step-off landings from equal heights

Although impact phase differences between vertical jump landings (VJL) and step-off landings (STL) may be related to task-specific pre-contact strategies, pre-contact mechanics are rarely examined. Thus, pre-contact kinematics and vertical ground reaction force (vGRF) impulse were examined between VJL and STL. Ten health adults (20.9 ± 1.6 yrs; 167.8 ± 4.2 cm; 68.5 ± 7.15 kg) performed 15 VJL and 15 STL from equal heights. Limb (lead; trail) by task (VJL; STL) ANOVAs (α = 0.05) compared hip, knee, and ankle joint angles 150 ms pre-contact, 100 ms pre-contact, 50 ms pre-contact, and at ground contact. Joint angular displacement was also evaluated between 150 ms pre-contact and ground contact. vGRF impulse was compared during the loading (ground contact to peak vGRF) and attenuation (peak vGRF to end of impact) phases. Greater hip flexion angles occurred during STL versus VJL at each event except 150 ms pre-contact (p ≤ .004). Trail limb knee flexion angles were greater at each event when compared to the lead limb during STL (p ≤ .019). Greater trail limb knee flexion angles occurred during STL versus VJL at all four events (p ≤ .018), while greater plantarflexion angles occurred at all four events during VJL versus STL (p ≤ .034). During STL, greater trail limb plantarflexion angles were detected at each event versus the lead limb (p < .001). Lesser hip, lead and trail limb knee displacement occurred during STL versus VJL (p < .05). Greater vGRF impulse was detected during the loading phase of VJL (<.001), while greater vGRF impulse occurred during the attenuation phase of STL (p = .025). These tasks are characterized by distinct pre-contact kinematic strategies and post-contact kinetics. The task utilized in practice should reflect the requirements of the population of interest.