Peak Ground Reaction Force Research Articles

Asymmetry in children with unilateral cerebral palsy during sit-to-stand movement: Cross-sectional, repeated-measures and comparative study

BackgroundWe aimed to compare motor strategies adopted by children with unilateral Cerebral Palsy and typically developing children during the performance of sit-to-stand. MethodsEleven children with unilateral cerebral palsy and 20 typically developing children were evaluated. Kinematic and kinetic analysis of the sit-to-stand movement was performed. Three seat heights were evaluated: neutral (90° of hip-knee-ankle flexion), elevated to 120% of the neutral height, and lowered to 80% of the neutral height. As outcome variables, we considered sit-to-stand duration (temporal); initial, final and maximal sagittal angles and range of motion of trunk, pelvis, hip, knee, and ankle (kinematics); the peak of vertical ground reaction force (kinetics), and asymmetric index. Effect size is represented by η2p. FindingsWe found that for the lowered seat, all groups presented increased flexion of lower limbs and trunk to initiate sit-to-stand (p≤0.012; η2p = 0.41–0.84), increased peak flexion of trunk, hip and knee (p≤0.01; η2p = 0.39–0.88), increased range of motion of knee and trunk (p≤0.01; η2p = 0.45–0.85) and the duration of sit-to-stand (p≤0.05 η2p = 0.23–0.56). Children with unilateral cerebral palsy presented increased posterior pelvic tilt (p≤0.01) and decreased hip flexion of both lower limbs (p≤0.01) for all seat heights and moved their non-affected limb backward in the lowered seat (p≤0.01). Asymmetry was observed for the final and the maximal angles of the ankle in neutral and lowered seats in unilateral cerebral palsy (asymmetry index = 3.3–5.8%). InterpretationThe lowered seat height led to adaptive motor strategies in children with unilateral cerebral palsy, which should be considered in clinical practice.

Acute effects of preventive warm-up exercises on modifiable risk factors for anterior cruciate ligament injuries: a three-arm randomized-controlled crossover trial.

We aimed to compare the potential acute effects of single bouts of a classic prevention and a risk factor-focus training aiming to target modifiable anterior cruciate ligament (ACL) rupture risk factors and the impact of neuromuscular fatigue on relevant ACL rupture risk factors. Two preventive warm-up (standard and ACL rupture risk factor training) and one inactive arm were compared; each of these were followed by a standardized neuromuscular fatigue protocol. The assessments included two Trail making tests (TMT-A; TMT-B, time to complete), drop jump landings (knee separation distance, normalized at hip width), as well as unanticipated counter movement jump landings (time to stabilization and peak ground reaction force). We included 18 participants (25±2years). No differences were found between times and conditions for TMT (P>0.05). A significant time effect occurred in time to stabilization (F=2.6; P<0.05) and a significant time*baseline-value*jumping time interaction was seen in peak ground reaction force (F=3.1; P<0.05). No time effect was found for any knee separation distance (F=.1-2.4; P>0.05); but a significant time*baseline-value*jumping time interaction was seen at initial ground contact (F=2.8; P<0.05), and lowest point (F=4.2; P<0.01). Risk factor-focus and classic warm-up may not differ in their acute effects on modifiable functional ACL (re-)injury risks factors.

Can shank acceleration provide a clinically feasible surrogate for individual limb propulsion during walking?

Aging and many pathologies that affect gait are associated with reduced ankle power output and thus trailing limb propulsion during walking. However, quantifying trailing limb propulsion requires sophisticated measurement equipment at significant expense that fundamentally limits clinical translation for diagnostics or gait rehabilitation. As a component of joint power, our purpose was to determine if shank acceleration estimated via accelerometers during push-off can serve as a clinically feasible surrogate for ankle power output and peak anterior ground reaction forces (GRF) during walking. As hypothesized, we found that young adults modulated walking speed via changes in peak anterior GRF and peak ankle power output that correlated with proportional changes in shank acceleration during push-off, both at the individual subject (R2 ≥ 0.80, p < 0.01) and group average (R2 ≥ 0.74, p < 0.01) levels. In addition, we found that unilateral deficits in trailing limb propulsion induced via a leg bracing elicited unilateral and relatively proportional reductions in peak anterior GRF, peak ankle power, and peak shank acceleration. These unilateral leg bracing effects on peak shank acceleration correlated with those in peak ankle power (braced leg: R2 = 0.43, p = 0.028) but those effects in both peak shank acceleration and peak ankle power were disassociated from those in peak anterior GRF. In conclusion, our findings in young adults provide an early benchmark for the development of affordable and clinically feasible alternatives for assessing and monitoring trailing limb propulsion during walking.

Hop-Stabilization Training and Landing Biomechanics in Athletes With Chronic Ankle Instability: A Randomized Controlled Trial.

Hopping exercises are recommended as a functional training tool to prevent lower limb injury, but their effects on lower extremity biomechanics in those with chronic ankle instability (CAI) are unclear. To determine if jump-landing biomechanics change after a hop-stabilization intervention. Randomized controlled clinical trial. Research laboratory. Twenty-eight male collegiate basketball players with CAI were divided into 2 groups: hop-training group (age = 22.78 ± 3.09 years, mass = 82.59 ± 9.51 kg, height = 187.96 ± 7.93 cm) and control group (age = 22.57 ± 2.76 years, mass = 78.35 ± 7.02 kg, height = 185.69 ± 7.28 cm). A 6-week supervised hop-stabilization training program that consisted of 18 training sessions. Lower extremity kinetics and kinematics during a jump-landing task and self-reported function were assessed before and after the 6-week training program. The hop-stabilization program resulted in improved self-reported function (P < .05), larger sagittal-plane hip- and knee-flexion angles, and greater ankle dorsiflexion (P < .05) relative to the control group. Reduced frontal-plane joint angles at the hip, knee, and ankle as well as decreased ground reaction forces and a longer time to peak ground reaction forces were observed in the hopping group compared with the control group after the intervention (P < .05). The 6-week hop-stabilization training program altered jump-landing biomechanics in male collegiate basketball players with CAI. These results may provide a potential mechanistic explanation for improvements in patient-reported outcomes and reductions in injury risk after ankle-sprain rehabilitation programs that incorporate hop-stabilization exercises.

Reliability and minimum detectable change of measures of gait in children during walking and running on an instrumented treadmill

BackgroundInstrumented treadmills that incorporate pressure platforms are increasingly used to characterize gait in children. Although footprint size is known to influence the measurement performance of pressure platforms, published evidence on the reliability of such systems for children’s gait is lacking. Research questionThis study evaluated the test–retest reliability of temporospatial gait parameters and vertical ground reaction forces measured in healthy children during barefoot walking and running on a capacitance–based treadmill system. MethodsTemporospatial gait parameters, including cadence, stride length, stride duration, stance and swing phase durations and the magnitude and timing of conventional vertical ground reaction force peaks were determined on two occasions in 17 healthy children (mean age, 11 ± 2 years; height, 148.4 ± 9.3 cm; and mass, 43.3 ± 10 kg) during walking and running at preferred speed on an instrumented treadmill. Reliability was assessed using Intra Class Correlation Coefficients (ICC) and the standard error of measurement (SEM). The minimum detectable change (MDC95%) was also calculated. ResultsICC values ranged from 0.91–0.99 for all variables. When expressed as a percentage of the mean, the SEM was <5% for all gait parameters assessed during walking and running. The MDC95% values for gait parameters were typically higher during running than walking, and were ±4% of the gait cycle for temporal parameters, ±55 cm for stride length and ±0.1 bodyweights for peak vertical ground reaction force. SignificanceChildren’s gait parameters varied by <5% between test occasions and were more consistent during walking than running. These findings provide clinicians and researchers with an index of the reliability and sensitivity of the treadmill to detect changes in common spatiotemporal gait parameters and vertical ground reaction forces in children.

Changes in running kinematics and kinetics after a 12-week running program for beginners

ABSTRACT The effect of running training on running kinematics and kinetics in novice runners has not yet been investigated. Previous studies have shown that novice runners are less economical and more prone to injury compared to well-trained runners. Since running economy (RE) and running injury risk have been associated with biomechanical variables that may be trainable, the purpose of this study was to determine the effect of a 12-week training program for beginners on running kinematics and kinetics. It was hypothesised that participants would evolve towards running kinematics and kinetics that have previously been associated with better RE and lower injury risk. 27 participants underwent a full-body, three-dimensional running analysis before and after a 12-week running program. Outcome variables included peak joint angles, joint moments, and ground reaction forces (GRF) in three planes. After training, hip external rotation moment increased significantly with 0.01 Nm/kg. Peak vertical GRF decreased with 0.9 N/kg (4.05%). There were no significant changes in peak joint angles. In conclusion, results show that a 12-week running program for beginners aimed to increase running endurance does not lead to changes in running kinematics or kinetics that have previously been associated with better RE and lower injury risk.

Are biomechanical stability deficits during unplanned single-leg landings related to specific markers of cognitive function?

ObjectivesCognitive skills such as working memory or inhibitory control are suggested to have an impact on injury risk during time-constrained athletic movements. Thus, the aim of this study was to gain further insights into the cognitive processes associated with biomechanical stability in unplanned jump-landings. DesignCross-sectional. MethodsTwenty male participants (27±4years) performed 70 counter-movement jumps with single-leg landings on a pressure plate. Equally balanced and in randomized order, these were to be performed either planned (landing leg indicated before take-off) or unplanned (visual cue during flight). Biomechanical stability was estimated from vertical peak ground reaction force (pGRF), time to stabilization (TTS), center of pressure path length (COP), and the number of standing errors (ground touch with free leg). In addition, decision-making was assessed as the amount of landing errors (wrong/both feet) in the unplanned condition. Cognitiive function was measured using computerized as well as pen-and-paper-testing. ResultsUnplanned landings produced higher COP values (p<0.001, d=1.1) and more standing errors (p<0.001, d=0.9) than the pre-planned condition. Decreased postural stability (COP) was related to lower inhibitory control (p=0.036, r=0.48). There was a correlation between the increase in standing errors and better cognitive flexibility/working memory (p=0.037, r=−0.48) and short-term memory (p=0.028, r=0.50). The opposite was found for the unplanned landing errors: poor decision-making was associated with deficits in cognitive flexibility/working memory (p=0.022, r=0.54) and short-term memory (p=0.019, r=−0.55). ConclusionsCognitive function may be an important, but under-researched moderator of unplanned jump-landing safety. Further research should elucidate the development of training methods aiming to improve movement-related decision-making and landing stability under time constraints.

Comparison of gait, functional activities, and patient-reported outcome measures in patients with knee osteoarthritis and healthy adults using 3D motion analysis and activity monitoring: an exploratory case-control analysis.

ObjectiveTo examine functional performance differences using kinematic and kinetic analysis between participants with and without knee osteoarthritis (OA) to determine which outcomes best characterize persons with and without knee OA.MethodsParticipants with unilateral moderate knee OA (Kellgren–Lawrence grades 2 or 3) and controls without knee pain were matched for age, gender, and body mass index. Primary outcomes included temporal parameters, joint rotations and moments, and ground reaction forces assessed via 3D motion capture during walking and ascending/descending stairs. Secondary outcomes included timed functional activities (sit to stand; tying shoelaces), 48 hrs lower limb activity monitoring, and patient-reported outcome measures (Knee Injury and Osteoarthritis Outcome Score, Western Ontario and McMaster Universities Osteoarthritis Index, European Quality of Life–5 Dimensions).ResultsEight matched pairs were analyzed. Compared with controls, OA participants exhibited significant reductions in peak frontal hip and sagittal knee moments, and decreased peak anterior ground reaction force with the affected limb while walking. Ascending stairs, OA participants had slower speed, fewer strides per minute, longer cycle and stance times, and increased trunk range of motion (ROM) in assessments of both limbs; longer swing time and reduced ankle ROM in the affected limb; and increased knee frontal ROM in the unaffected limb. Descending stairs, OA participants had fewer strides per minute and decreased trunk transverse ROM in assessments of both limbs; increased knee frontal ROM in the affected limb; and longer strides, shorter stance and cycle times, increased trunk sagittal and decreased knee transverse ROMs in the unaffected limbs vs controls. Compared with controls, OA participants had slower walking cadence (120–130 vs 100–110 steps/min, respectively), took significantly longer on timed functional measures, and had significantly worse scores in patient-reported outcomes.ConclusionSeveral objectives and patient-reported measures examined in this study could potentially be considered as outcomes in pharmacologic or physical therapy OA trials.

Reliability of Squat Kinetics in Well-Trained Rugby Players: Implications for Monitoring Training.

Appleby, BB, Cormack, SJ, and Newton, RU. Reliability of squat kinetics in well-trained rugby players: implications for monitoring training. J Strength Cond Res 33(10): 2635-2640, 2019-The aim of this study was to determine the within-session reliability in kinetic variables of the squat in well-trained athletes during a typical resistance training protocol. Fifteen subjects completed 2 testing sessions. Session 1 was establishment of 1 repetition maximum (1RM) squat, and session 2 involved 2 sets of 2 maximal effort repetitions of the squat at 70, 80, and 90% of 1RM with 3D motion analysis and ground reaction force (GRF) measurement using 2 in-ground triaxial force plates. Reliability was calculated using typical error ± 90% confidence limits, expressed as the coefficient of variation and intraclass correlation coefficient. The smallest worthwhile change (SWC%), calculated as 0.2 × between-subject SD, was used to determine the smallest important change in performance. Peak GRF and average GRF were found to have acceptable measures of reliability with the combined left and right leg average GRF capable of detecting the SWC. Independent limb contributions were reliable (left and right, or dominant and nondominant). Reliable kinetics can be obtained in back squat performance typical of a resistance training session in well-trained athletes. This suggests that coaches integrating force plate technology within training sessions may effectively capture between 1 and 6 training sets among several athletes, facilitating analysis and intervention on larger data sets.

The Effect of Preparatory Posture on Goalkeeper's Diving Save Performance in Football.

Identifying the optimal preparatory posture of football goalkeepers can be very relevant for improving goalkeepers' diving save performance, and coaching practices of technical and strength and conditioning coaches. This study aimed to analyse the effect of different starting stance widths and knee flexion angles on movement time, center of mass (CoM) trajectory and velocity in goalkeepers' diving saves. Ten elite goalkeepers performed dives from preferred (PT) and imposed postures, by altering knee angle (45, 75, and 90°) and stance width (50, 75, and 100% of leg length) independently, at the starting position. Repeated measures ANOVA showed a main effect of preparatory posture on dive time (p < 0.01). Pairwise comparisons showed that the fastest dive movement time was observed when goalkeepers started from a stance width of 75% (SW75). CoM traveled a larger distance between contralateral and ipsilateral peak ground reaction forces in SW75 than PT (p < 0.05). The goalkeepers were also more efficient in SW75, as a smaller countermovement and vertical velocity range were observed during high and low dives, respectively, from SW75 than PT (p < 0.05). Thus, diving from a position with wider stance width than the preferred one leads to shorter movement time, and a faster and more direct CoM trajectory toward the ball.

Comparison of Peak Ground Reaction Force, Joint Kinetics and Kinematics, and Muscle Activity Between a Flexible and Steel Barbell During the Back Squat Exercise.

The flexible barbell is purported to improve training gains compared with an Olympic steel barbell (SB) during the back squat exercise with Division I collegiate American football programs. The two bars loaded at 30% 1-repetition maximum were compared with ten trained Division I American football players (n = 10; age = 19.5 years; body mass = 89.4 kg; body height = 182.0 cm) completing 10 repetitions of the back squat exercise. Analysis included integrated-peak values of electromyography of the rectus femoris, biceps femoris, rectus abdominis, erector spinae, external oblique, vastus lateralis, ground reaction forces, and joint kinematics and kinetics of the hip, knee, and ankle. The flexible bar elicited significant increases in peak joint kinetics (Hip Moment: 229 ± 54 Nm vs. 209 ± 52 Nm; Hip Power: 494 ± 151 W vs. 382 ± 134 W; Knee Power: 305 ± 108 W vs. 241 ± 63 W), peak vertical ground reaction forces (1195 ± 209 N vs. 1120 ± 203 N), and muscle activity (Vastus Lateralis: 75.7 vs. 66.5%, Rectus Abdominis: 190 vs. 115%, Rectus Femoris: 69.8 vs. 59.9%, External Oblique: 115 vs. 69.0%). Greater vertical ground reaction forces, hip moment, hip power, knee power, and muscle activity of the vastus lateralis, rectus abdominis, rectus femoris, and external oblique suggest the FB provides biomechanical and physiological mechanisms for training gains over the SB for 30% of 1-repetition maximum loads.

Ground reaction forces of overground galloping in ridden Thoroughbred racehorses.

The horse has evolved to gallop economically at high speed. Limb force increases with speed but direct measures of limb ground reaction forces (GRFs) at gallop are sparse. This study reports GRFs for multiple limbs, using force plates, across seven Thoroughbred racehorses during ridden galloping. The results show peak vertical GRF values of 13.6 N kg-1 (non-lead hindlimb), 12.3 N kg-1 (lead hindlimb), 14.0 N kg-1 (non-lead forelimb) and 13.6 N kg-1 (lead forelimb) at 11.4 m s-1 and recorded values are consistent with those predicted from duty factor. The distribution of body weight between the forelimbs and hindlimbs is approximated to 50:50, and is variable with speed, unlike the 60:40 commonly stated for cursorial quadrupeds in the literature. An even distribution of load on all limbs may help minimise accumulation of fatigue and assist in injury avoidance. Cranio-caudal force data concur with the observation that horses apply a net accelerative impulse with the hindlimbs and a net decelerative impulse with the forelimbs. Capturing GRFs enhances our knowledge on the mechanics of galloping in fast-moving species and provides insight into injury risk and factors limiting athletic performance.

Unanticipated jump-landing after anterior cruciate ligament reconstruction: Does unanticipated jump-landing testing deliver additional return to sport information to traditional jump performance tests?

BackgroundWe aimed to delineate if unanticipated jump-landing assessments delivers complementary information to those of commonly used hop and jump tests after anterior cruciate ligament reconstruction. MethodsEleven participants (5 males) performed a series of unanticipated jump-landings and traditional hop and jump performance tests (single leg hops for distance, triple crossover hops for distance and drop jumps). The number of mistrials, time to stabilization and peak ground reaction force (pGRF) at landing and jump/hop distance were measured. Pearson correlations to find potential associations between the unanticipated jump-landing-values and the traditional jump/hop performance tests were calculated twice: once for the affected and once for the unaffected legs. t-Tests for dependent samples were used to detect differences between affected and unaffected leg within each test condition. FindingsThe pGRF at unanticipated landing significantly correlated to the pGRF at drop jump landing (r = 0.68) and the hopping distance after the triple crossover hops (r = 0.71, each p < .05). No other significant correlation occurred (p > .05). Hopping distance after single leg hops (mean: 110.2 cm vs. 95.5 cm) and triple crossover hops for distance (mean: 315.3 cm vs. 294.2 cm) showed significant differences between the unaffected and the reconstructed leg (p < .05). Other parameters showed no significant between-legs differences (p > .05). InterpretationBoth, the reconstructed and the contralateral leg seems to be affected. Unanticipated jump landing tasks deliver information beyond those of commonly used jump and hop tests, the thereby assessed abilities may thus be a complementary aspect of dynamic knee function than those assessed with classic tests.

Kinetic Contributions of The Upper Limbs During Counter-Movement Verical Jumps With and Without Arm Swing.

Mosier, EM, Fry, AC, and Lane, MT. Kinetic contributions of the upper limbs during countermovement. J Strength Cond Res 33(8): 2066-2073, 2019-This study examined the kinetic contributions of the upper extremities during countermovement vertical jumps (CMVJs) while using arm swing (AS) or no arm swing (NAS) conditions. Fourteen healthy men ((Equation is included in full-text article.)± SD; age = 24.1 ± 3.9 years) volunteered for this investigation. Subjects performed in random order a total of 6 jumps consisting of 3 AS and 3 NAS CMVJs. A motion capture system was used to analyze the kinetic data. Paired samples t-tests were used to examine the subjects' mean differences in the AS and NAS CMVJ trials (p<0.05). Results for all subjects were determined for each jump subjects were determined for each jump performed, with statistical analyses performed on mean values for all 3 jumps per subject. The AS significantly increased the vertical jump height (VJH) by an average of 0.07 ± 0.03 m (3.0 ± 1.3 inches). Dual-energy X-ray absorptiometry scans determined that the upper limbs were 12.0% of the total body mass. Movement of the upper limbs during the AS CMVJ produced 32.2 ± 7.0% of the total mean ground reaction force (GRF), and 11.3 ± 2.2% during the NAS CMVJ. The enhancement of performance when jumping using an AS resulted in a 13.6% increase in VJH. The contribution of the upper limbs during the AS CMVJ averaged 31.5% of the peak GRF, which occurred immediately before takeoff. The upper extremities can greatly influence vertical jump performances and the accompanying kinetics. When analyzing jump GRFs, one must be aware of how much the upper limbs contribute to these forces. In addition, proper AS mechanics must be emphasized when instructing correct jump technique.

The relationship between leg stiffness, forces and neural control of the leg musculature during the stretch-shortening cycle is dependent on the anticipation of drop height.

This study aimed at investigating how prior knowledge of drop heights affects proactive and reactive motor control in drop jumps (DJ). In 22 subjects, the effect of knowledge of three different drop heights (20, 30, 40cm) during DJs was evaluated in seven conditions: three different drop heights were either known, unknown or cheated (announced 40cm, but actual drop height was 20cm). Peak ground reaction force (Fmax) to body weight (BW) ratio (Fmax/BW) and electromyographic (EMG) activities of three shank and five thigh muscles were assessed 150ms before and during ground contact (GC). Ankle, knee and hip joint kinematics were recorded in the sagittal plane. Leg stiffness, proactive and reactive EMG activity of the leg muscles diminished in unknown and cheat conditions for all drop heights (7-33% and 2-26%, respectively). Antagonistic co-activation increased in unknown (3-37%). At touchdown, increased flexion in knee (~ 5.3° ± 1.9°) and hip extension (~ 2° ± 0.6°) were observed in unknown, followed by an increased angular excursion in hip (~ 2.3° ± 0.2°) and knee joints (~ 5.6° ± 0.2°) during GC (p < 0.05). Correlations between changes in activation intensities, joint kinematics, leg stiffness and Fmax/BW (p < 0.05) indicate that anticipation changes the neuromechanical coupling of DJs. No dropouts were recorded. These findings underline that anticipation influences timing and adjustment of motor responses. It is argued that proactive and reactive modulations associated with diminished activation intensities in leg extensors are functionally relevant in explaining changes in leg stiffness and subsequent decline in performance.

Vertical Ground Reaction Force During a Water-Based Exercise Performed by Elderly Women: Equipment Use Effects

ABSTRACTPurpose: The present study aimed to compare the vertical ground reaction force responses during the performance of the stationary running water-based exercise with and without equipment at different cadences by elderly women. Method: Nineteen elderly women (age: 68.6 ± 5.0 years; body mass: 69.0 ± 9.5 kg; height: 154.9 ± 5.6 cm) completed one session consisting of the performance of the water-based stationary running with elbow flexion and extension immersed to the xiphoid process depth. The exercise was performed in three conditions, without equipment, with water-floating and with water-resistance equipment, at three cadences (80 b·min−1, 100 b·min−1 and maximal) in a randomized order. Peak and impulse of vertical ground reaction force were collected during the exercise using an underwater force plate. Repeated measures two-way ANOVA was used (α = 0.05). Results: Peak vertical ground reaction force (p < .001) and impulse (p ≤ 0.002) resulted in lower values for the water-floating use (0.42–0.48 BW and 0.07–0.13 N.s/BW) in comparison to the water-resistance equipment use (0.46–0.60 BW and 0.09–0.16 N.s/BW) and to the non-use of equipment (0.45–0.60 BW and 0.07–0.17 N.s/BW), except for the impulse at the maximal cadence. In addition, peak vertical ground reaction force at 80 b·min−1 (p = .002) and impulse at the maximal cadence (p < .001) showed lower values compared to the other cadences. Conclusion: The use of water-floating equipment minimizes the vertical ground reaction force during the stationary running water-based exercise performed by elderly women regardless of the cadence.

Percentage Contribution of Lower Limb Moments to Vertical Ground Reaction Force in Normal Gait

ObjectiveThe purpose of this study was to investigate how the hip, knee, and ankle moments in the sagittal plane contribute to the vertical ground reaction force (GRF) in healthy participants during normal speed of walking. MethodsForty healthy male individuals volunteered to participate in this study. They were filmed using 6 high-speed (120 Hz) Pro-Reflex infrared cameras (Qualisys) while walking on an Advanced Mechanical Technology Incorporation force platform. The data collected were the percentage contribution of the moments of the hip, knee, and ankle joints in the sagittal plane at the instant of occurrence of the first peak, second peak, and trough of the vertical GRF. ResultsThe results revealed that at the first peak of the GRF (loading response), the highest contribution was generated from the knee extension moment followed by the hip extension moment. Knee flexion and ankle plantar flexion moments produced a high contribution to the trough of the GRF (midstance) with approximately equal values. The second peak of the GRF was mainly produced by the ankle plantar flexion moment. ConclusionThe role of hip extension moment is secondary to knee extension moment in the first peak of GRF. Knee flexion moment is secondary to ankle plantar flexion moment in the second peak of GRF. Both knee flexion and ankle plantar flexion moments have equal contribution during midstance.

Effects of Shock Pad and Synthetic Turf on Ankle Biomechanics in a 90° Cutting Movement

Shock pad (PAD) is a popular choice underlayment installed under a synthetic turf (TURF) field. The effects of PAD on impact attenuation and injury risks of human movements are still relatively unknown. PURPOSE: To examine impact attenuation related ankle biomechanical characteristics of a 90° cutting movement on synthetic turf with shock pad compared to synthetic turf only. METHODS: Twelve recreational football and soccer players performed five successful trials of 90° cutting movement in each of two approaching speed conditions: 3.0±0.3 (SLOW) and 4.0±0.4 (FAST) m/s on each of TURF and PAD surface conditions. Three-dimensional kinematic and ground reaction force (GRF) data were collected simultaneously. A 2” monofilament synthetic turf with 1/2” stitch gauge was used in TURF and PAD conditions. A foam-based shock pad was used in PAD condition. RESULTS: No significant surface main effect or surface by speed interactions were found for any ankle kinematic and kinetic variables and peak GRFs (p > 0.05). Increased peak ankle eversion moment (0.65 vs. 0.84 Nm/kg, p<0.001) and inversion loading range of motion (ROM, 13.7 vs. 18.6 deg, p=0.001) were seen in FAST compared to SLOW. Increases for peak ankle sagittal-plane concentric pushoff power, and frontal-plane eccentric and concentric power were also observed in FAST compared to SLOW. Peak vertical (2.04 vs. 2.31 BW, p=0.023) and medial loading (0.79 vs. 1.11 BW, p=0.002) GRFs were higher in FAST than SLOW. Additionally, peak pushoff medial GRFs were increased from SLOW to FAST (0.91 vs. 1.20 BW, p=0.025), but pushoff vertical GRFs were decreased slightly (2.24 vs. 2.11 BW, p=0.011). CONCLUSIONS: The lack of significant differences between TURF and PAD and their interactions for examined ankle and GRF variables suggest that adding a form-based shock pad does not impede cutting performance. These results also seem to indicate there is a neuromuscular accommodation in cutting mechanics on PAD surface, which cannot be reflected loading variables using inverse dynamics. As cutting speed increased, greater increases in medial peak GRFs, and frontal-plane peak ankle moment and ROM were observed compared to those in sagittal-plane, suggesting increased mediolateral loading to ankle complex in fast cut movement. Supported in part by Brock International.

Manipulating Initial Peak vGRF During Walking Affects Loading Throughout Stance in Individuals with ACL Reconstruction

Gait alterations may be associated with osteoarthritis development following anterior cruciate ligament reconstruction (ACLR). Novel gait retraining paradigms are being developed to optimize peak vertical limb loading in the first half of stance; yet the effect of changing this single discrete variable on loading characteristics across the entire stance phase remain unknown. PURPOSE: Determine the effect of increasing and decreasing the first peak of the vertical ground reaction force (vGRF) by 5% during walking using real-time biofeedback (RTBF) of vGRF throughout stance. METHODS: 30 ACLR participants (21 females, 20.4±2.9 yrs, 172.7±10.8 cm, 73.2±16.1 kg, 47.8±4.2 months post-ACLR) completed one 20-minute control condition and two experimental conditions (high- and low-loading). For high- and low-load conditions, participants walked for 20 minutes on a force-measuring treadmill with RTBF displayed on a screen cuing a 5% increase (high) or decrease (low) in the first peak of the vGRF relative to vGRF collected in the control condition. VGRFs were collected at 1000 Hz throughout the 19th minute. Two functional analyses of variance were conducted to evaluate VGRF magnitude throughout stance. RESULTS: Figures 1A and 1C depict mean vGRF, normalized to body weight (BW), throughout the stance phase. Figures 1B and 1D depict pairwise comparison functions (solid black lines) and associated 95% confidence intervals (gray bands), indicating mean differences between the two conditions. Significant between-condition differences existed in the high-loading condition between 42 and 74% of stance, and in the low-loading condition (between 38 and 70%, and 76 and 97% of stance. CONCLUSION: RTBF, used to cue changes in the first vGRF peak, results in loading alterations throughout stance. Specifically, high loading results in lesser vGRF at midstance but a similar propulsive peak. Conversely, low loading increases vGRF during midstance and decreases vGRF during toe-off.

Cognition Matters: Brain Function May Explain Deficiencies In Unanticipated Single-leg Landing Quality

It has been speculated that cognitive performance may play a role in injury risk during sports-related movements such as jump landings. However, there is a paucity of research concerning this hypothesis. PURPOSE: The present study aimed to elucidate the potential association between brain function and biomechanical stability as well as decision-making success in an unanticipated jump-landing task. METHODS: Twenty healthy male participants (27±4 years) performed 70 counter-movement jumps with single-leg landings (n=35 anticipated/ unanticipated each) on a pressure plate. In the anticipated condition, the required landing leg was indicated already before take-off. For the unanticipated jumps, this information was presented only during the flight phase. Biomechanical landing quality was estimated from vertical peak ground reaction force (pGRF), time to stabilization (TTS), center of pressure path way (COP), and standing errors (i.e. falls, touching the ground with the free leg). Decision-making accuracy was assessed as the amount of landing errors (wrong/both feet). Differences between conditions as well as their associations with several measures of cognitive function were analyzed controlling for relevant covariates. RESULTS: Unanticipated landings resulted in higher COP values (588 vs. 516mm, p<.001, d=.65) and more standing errors (n=2.1 vs. 0.3, p<.001; d=1.1) than anticipated trials. While the biomechanical deficit was not related to cognitive function (p>.05), there was an unexpected correlation between the increase in standing errors and higher cognitive flexibility (r=-.481, p=.037) as well as better working memory capacity (r=.502, p=.028). An opposite pattern was found for the landing errors occurring in the unanticipated condition: poor decision-making was associated with deficits in cognitive flexibility (r=.609; p<.001) and working memory (r=-.500; p< .05). CONCLUSIONS: Cognitive function may be an important but understudied moderator of unanticipated jump landing safety. Further research should be dedicated to the development of specific training methods aiming to improve movement-related decision-making under time constraints.