Peak GRF Research Articles

The Injury Risk Prediction of Firefighters with Biomechanical Parameters during Single- and Double-Leg Jumps

The incidence of knee injuries during firefighter training is high, but there is a lack of research on predictive factors and risk assessment for such injuries. Biomechanical assessments can provide a better understanding of how the body’s load changes during exercise, which may alter the risk of injury. Ten firefighters were recruited for our study. Each participant completed the FMS test and the single- and double-leg jump tasks. Motion information was collected and musculoskeletal models of the participants were constructed using OpenSim 4.4 to obtain the joint angle and joint moment. The peak GRF and CoM-CoP angle were also calculated. The findings showed a significantly larger PKFM (p = 0.0195), VAFM (p = 0.0039), and peak AP GRF (p = 0.0039) during the single-leg jump. The opposite performance was observed for KFA (p = 0.0098) and MPA (p = 0.0273). A stepwise multiple linear regression analysis was used to explore the relationship between these parameters and both the FMS score and the times of injuries. The risk of injury is higher in the single-leg jump compared to the double-leg jump. The biomechanical parameters of these two jumps can be used to assess sports injuries and to provide methods and references for injury risk monitoring during firefighter occupational training.

Differences in Physical Characteristics of the Lower Extremity and Running Biomechanics Between Different Age Groups.

(1) Background: The objective of this study was to determine physical and biomechanical changes in age groups upon running. (2) Method: 75 male adults (20–80s) participated in the study. Bone mineral density and lower extremity joint strength were measured according to age-increase targeting. Based on age, correlations among running characteristics, impulse, impact force, maximum vertical ground reaction force, loading rate, lower extremity joint 3D range of motion, joint moment, and power upon running motion were calculated. (3) Result: Older runners tended to show lower bone mineral density, extremity maximum strength, stride time, and stride distance, with smaller RoM and joint power of ankle and knee joints in the sagittal plane, compared with younger subjects. However, there were no significant correlations between age and impact variables (i.e., impulse, impact force, peak GRF, and loading rate) during running. (4) Conclusion: Older runners tend to show weaker physical strength characteristics, such as bone mineral density and muscle strength and lower joint functionality of ankle and knee joints during running, compared with younger runners. Therefore, strengthening the lower extremity muscle and improving dynamic joint function, especially for ankle joints, can be helpful for injury prevention during running.

Maximal Strength in Relation to Force and Velocity Patterns During Countermovement Jumps.

To investigate the associations between maximal strength and GRF and COM velocity patterns during CMJ. Nineteen female college lacrosse players performed 3 maximal-effort CMJs and isometric midthigh pull. GRF and COM velocity time series data from the CMJ were time normalized and used as inputs to principal-components analyses. Associations between isometric midthigh pull peak force and CMJ principal-component scores were investigated with a correlational analysis. Isometric midthigh pull peak force was associated with several GRF and COM velocity patterns. Correlations indicated that stronger players exhibited a GRF pattern characterized by greater eccentric-phase rate of force development, greater peak GRF, and a unimodal GRF profile (P = .016). Furthermore, stronger athletes exhibited a COM velocity pattern characterized by higher velocities during the concentric phase (P = .004). Maximal strength is correlated to specific GRF and COM velocity patterns during CMJ in female college lacrosse athletes. Since maximal strength was not correlated with discrete CMJ variables, the patterns extracted via principal-components analyses may provide information that is more beneficial for performance coaches and researchers.

Is There An Optimal Vertical Ground Reaction Force Profile For Maximizing Jump Height In A Countermovement Jump?

PURPOSE: The vertical ground reaction force (VGRF) during a countermovement jump (CMJ) is classically described with a single peak force occurring at the low position of the countermovement. However, in practice, jumpers display a variety of CMJ VGRF profiles, including single and double peaks, and jumps where the peak force occurs at, or after, low position. The purpose of this study was to identify the optimal CMJ VGRF profile for maximizing jump height. METHODS: The top 100 CMJs (based on jump height) from a database of over 2000 jumps, from 211 division one college athletes were analyzed. The 100 athletes (21±3 yr, 96 men) were from several different sports teams (hockey n=33, lacrosse n=25, soccer n=14, basketball n=14, other n=14). All jumps were performed with the hands on the hips. Jumps were categorized as having a single or a double peak in VGRF and whether the peak GRF occurred at, after, or before low position. Jump heights were categorized as above average (1SD>mean), average (within 1SD of mean), or below average (1SD<mean). The association between jump metrics and VGRF profiles was examined using chi square analyses and independent t-tests. RESULTS: Of the 100 CMJs 22 had a single peak VGRF, of which 14 occurred at low position and 8 occurred after low position. Of the 78 CMJs with a double peak, the 1st peak was higher in 47 jumps (30 at low position, 13 after low position, 4 before low position), the peaks were equal in 20 jumps (10 at low position, 10 after low position), and the 2nd peak was higher in 11 (all after low position). Peak GRF occurred at the low point of the countermovement for 82% (14 of 17) of the above average jumps versus 52% (33 of 64) of the average jumps and only 37% (7 of 19) of the below average jumps (P=0.007). For the 78 jumps with two distinct VGRF peaks the 1st peak was greater than the 2nd for 77% (10 of 13) of above average jumps, 61% (30 of 49) of average jumps and only 44% (7 of 16) of below average jumps (P=0.033). CONCLUSIONS: The optimal VGRF profile appeared to be peak force occurring at low position regardless of whether there was a single or double peak. The worst VGRF profile appeared to be jumps with two peaks where the 2nd peak was greater than the 1stpeak, or the 1st and 2nd peaks were equal, but the 1st peak occurred after low position. In conclusion, achieving peak VGRF at the low position of a CMJ appears to be optimal.

Effect of shoe wearing time and midsole hardness on ground reaction forces, ankle stability and perceived comfort in basketball landing

ABSTRACT This study examined the effect of wearing time on comfort perception and landing biomechanics of basketball shoes with different midsole hardness. Fifteen basketball players performed drop landing and layup first step while wearing shoes of different wearing time (new, 2-, 4-, 6- and 8-week) and hardness (soft, medium and hard). Two-way ANOVA with repeated measures was performed on GRF, ankle kinematic and comfort perception variables. Increased wearing time was associated with poorer force attenuation and comfort perception during landing activities (p < 0.05). The new shoes had significantly smaller forefoot (2- and 4-week) and rearfoot peak GRF impacts (all time conditions) in drop landing and smaller rearfoot peak GRF impact (6- and 8-week) in layup; shoes with 4-week of wearing time had significantly better perceptions of forefoot cushioning, forefoot stability, rearfoot cushioning, rearfoot stability and overall comfort than the new shoes (p < 0.05). Compared with hard shoes, the soft shoes had better rearfoot cushioning but poorer forefoot cushioning (p < 0.05). Shoe hardness and wearing time would play an influential role in GRF and comfort perception, but not in ankle kinematics. Although shoe cushioning performance would decrease even after a short wearing period, the best comfort perception was found at 4-week wearing time.

Cadence impact on cardiopulmonary, metabolic and biomechanical loading during downhill running

BackgroundDistance runners can approach long descents with slow cadence and long steps, or a fast cadence with shorter steps. These approaches differentially affect mechanical loading and energy demand. Research questionThis study determined the cadence range in which biomechanical loads, caloric unit cost and energy cost were simultaneously minimized during downhill running (DR). MethodsTrained runners (N = 40; 25.6 ± 7.2 yr; 42.5% female) participated in this experimental study. Participants ran on an instrumented treadmill while wearing a portable gas analyzer during six conditions: control normal level running (LR) at 0 deg inclination (CON-0); control DR -6 deg inclinaton (CON-6); DR at cadences +/-5% and +/-10% different from CON-6. A motion analysis system was used to capture running motion, and an instrumented treadmill captured force data. Cardiopulmonary measures, rating of perceived exertion (RPE), and biomechanical measures (temporal spatial parameters, peak ground reaction forces [GRF], vertical average loading rate [VALR], impulses) were calculated. Caloric unit cost and energy costs were standardized per unit distance. ResultsRunning at -10% cadence increased HR by 10 bpm compared to CON-6 (p < 0.0001). Vertical excursion of the center of mass and step length were greatest in the cadence -10% and least in the cadence +10% conditions (both p < 0.0001). RPEs were higher among all cadence conditions compared to CON-0 (p < 0.0001). Caloric unit costs were lowest in CON-6, and +/5% cadence conditions compared to the CON-0 and +/-10% conditions (-2.1% to -12.3%, respectively; p < 0.05). Peak GRF and VALR were not different among conditions; vertical impulses were greatest in the -10% condition compared to CON-0, CON-6 and +5% and +10% by 11.3–14.5% (p < .001). SignificanceChanging cadence across level and downhill stretches is likely not necessary and may actually increase perceived effort of running. Running downhill at cadences that range +/-5% of preferred simultaneously minimize caloric unit cost and impulse loading.

Increased knee loading in stair ambulation in patients dissatisfied with their total knee replacement

BackgroundTotal knee replacement patients have shown reductions in knee flexion range of motion, knee extensor moments, and gait speed during stair ascent and stair descent. However, it is unknown how patients dissatisfied with their total knee replacement differ from those who are satisfied during more difficult activities such as stair negotiation. Therefore, the purpose of this study was to compare knee biomechanics of patients who are dissatisfied with their joint replacement to those who are satisfied and healthy participants during stair negotiation. MethodsNine dissatisfied, fifteen satisfied patients and fifteen healthy participants participated, completing stair ascent and descent trials on an instrumented staircase. A 2 × 3 ANOVA was used to analyze biomechanical differences between groups and limbs during both activities. FindingsThe dissatisfied group showed reduced 2nd peak vertical GRF (P ≤ 0.0040) and loading-response knee extension moments (P ≤ 0.0041) in their operated limb compared to their non-operated limb and to satisfied and healthy groups during stair ascent. First peak vertical GRF (P < 0.0088) and both loading-response (P < 0.0117) and push-off abduction moments (P < 0.0028) showed reduced values in operated limbs compared to non-operated limbs for all groups. During stair descent, the dissatisfied group showed reduced loading-response and push-off knee extension moments (P ≤ 0.006) in their operated limb compared to their non-operated limb and the healthy group. The loading-response knee extension (P < 0.0379) and abduction moments (P ≤ 0.0048) were also reduced in the dissatisfied group compared to the satisfied group. InterpretationPatients who were dissatisfied showed asymmetrical loading of the knees in conjunction, which may have contributed to their dissatisfaction.

Validation of a wireless shoe insole for ground reaction force measurement

ABSTRACTGround reaction force measurements are a fundamental element of kinetic analyses of locomotion, yet they are traditionally constrained to laboratory settings or stationary frames. This study assessed the validity and reliability of a new wireless in-shoe system (Novel Loadsol/Pedoped) for field-based ground reaction force measurement in hopping, walking, and running. Twenty participants bilaterally hopped on a force plate and walked (5 km/hr) and ran (10 km/hr) on an instrumented treadmill on two separate days while wearing the insoles. GRFs were recorded simultaneously on each respective system. Peak GRF in hopping and peak GRF, contact time (CT), and impulse (IMP) in walking and running were compared on a per-hop and step-by-step basis. In hopping, the insoles demonstrated excellent agreement with the force plate (ICC: 0.96). In walking and running, the insoles demonstrated good-to-excellent agreement with the treadmill across all measures (ICCs: 0.88–0.96) and were reliable across sessions (ICCs within 0.00–0.03). A separate verification study with ten participants was conducted to assess a correction algorithm for further agreement improvement but demonstrated little meaningful change in systemic agreements. These results indicated that the Novel Loadsol system is a valid and reliable tool for wireless ground reaction force measurement in hopping, walking, and running.

Understanding the impact loading characteristics of a badminton lunge among badminton players.

BackgroundThe rapid and repetitive badminton lunges would produce strenuous impact loading on the lower extremities of players and these loading are thought to be the contributing factors of chronic knee injuries. This study examined the impact loading characteristics in various groups of badminton athletes performing extreme lunges.MethodsFifty-two participants classified into male skilled, female skilled, male unskilled, and female unskilled groups performed badminton lunge with their maximum-effort. Shoe-ground kinematics, ground reaction forces, and knee moments were measured by using synchronised force platform and motion analysis system. A 2 (gender) x 2 (skill-level) factorial ANOVA was performed to determine the effects of different gender and different playing levels, as well as the interaction of two factors on all variables.ResultsMale athletes had faster approaching speed (male 3.87 and female 1.08 m/s), longer maximum lunge distance (male 1.47 and female 1.16 m), larger maximum (male 215.7 and female 121.65 BW/s) and mean loading rate (male 178.43 and female 81.77 BW/s) and larger peak knee flexion moment (male 0.75 and female 0.69) compared with female athletes (P < 0.001). Unskilled athletes exhibited smaller footstrike angle (skilled 45.78 and unskilled 32.35°), longer contact time (skilled 0.69 and unskilled 0.75 s), larger peak horizontal GRF (skilled 1.61 and unskilled 2.40 BW), smaller mean loading rate (skilled 150.15 and unskilled 110.05 BW/s) and larger peak knee flexion moment (P < .05; skilled 0.69 and unskilled 0.75 Nm/BW) than the skilled athletes. In addition, the interaction indicated greater peak GRF impact in female unskilled athletes compared with female skilled athletes (P < 0.001; female skilled 2.01 and female unskilled 2.95 BW), while there was no difference between male participants (P > 0.05; male skilled 2.19 and male unskilled 2.49 BW).ConclusionsThese data suggested that male athletes and/or unskilled athletes experience greater impact loading rates and peak knee flexion moment during lunge compared with female and skilled athletes, respectively. This may expose them to higher risk of overuse injuries. Furthermore, female unskilled athletes seemed to be more vulnerable to lower extremity injuries.

The effect of leg dominance and landing height on ACL loading among female athletes

Female athletes are more prone to anterior cruciate ligament (ACL) injury. A neuromuscular imbalance called leg dominance may provide a biomechanical explanation. Therefore, the purpose of this study was to compare the side-to-side lower limb differences in movement patterns, muscle forces and ACL forces during a single-leg drop-landing task from two different heights. We hypothesized that there will be significant differences in lower limb movement patterns (kinematics), muscle forces and ACL loading between the dominant and non-dominant limbs. Further, we hypothesized that significant differences between limbs will be present when participants land from a greater drop-landing height. Eight recreational female participants performed dominant and non-dominant single-leg drop landings from 30 to 60cm. OpenSim software was used to develop participant-specific musculoskeletal models and to calculate muscle forces. We also predicted ACL loading using our previously established method. There were no significant differences between dominant and non-dominant leg landing except in ankle dorsiflexion and GMED muscle forces at peak GRF. Landing from a greater height resulted in significant differences among most kinetics and kinematics variables and ACL forces. Minimal differences in lower-limb muscle forces and ACL loading between the dominant and non-dominant legs during single-leg landing may suggest similar risk of injury across limbs in this cohort. Further research is required to confirm whether limb dominance may play an important role in the higher incidence of ACL injury in female athletes with larger and sport-specific cohorts.

Validation Of Smartphone-based Assessment Of Sit-to-stand Power

Modern smartphones are inexpensive, portable, user friendly, and contain sensitive gyroscopes. Apps can be used to sample, store, and wirelessly transmit data. Although easy to conduct, field tests of sit-to-stand (STS) power provide only a relatively crude (timed or counted) outcome measure of global performance. Expensive lab-based biomechanics equipment is required to obtain measures of leg power (LP) for individual repetitions during brief 5x STS tasks. PURPOSE: To determine the ability of the iPod to detect movement speed for each rep during a 5x STS test, and make comparisons with an electrogoniometer (eGONI) and force platform. METHODS: Young adults (22.9 ± 2.9yrs, 21 men, 21 women) performed a 5x STS task as rapidly as possible with strict form. Three trials were performed. A 5th generation iPod Touch was firmly attached (Velcro) to a strap around the lower thigh. An eGONI (Biometrics) was placed laterally across the knee joint. The feet were on a force platform (AMTI Accusway) in front of the chair. Concurrently, iPod gyroscope data (rad), knee joint angle (rad), and ground reaction force (GRF, N) were sampled at 100Hz. The peak slope (0.1s time constant) of the iPod pitch signal, eGONI signal, and GRF was calculated for the rising phase of each rep. The peak GRF was also measured. The instantaneous slope was normalized to body mass to provide an index of power for each rep. For each device, the mean power of 5 reps and the maximal single rep value was calculated for the three trials. Correlations were computed between the devices across all subjects. RESULTS: The mean (R2=0.85) and max (R2=0.86) iPod peak slope were highly correlated with the corresponding eGONI value. The mean (R2=0.47) and max (R2=0.44) iPod peak slope were moderately correlated with the corresponding GRF value. The mean and max values were highly correlated with each other for the iPod (R2=0.99), eGONI (R2=0.99), and GRF (R2=0.98). The greater rising power for men vs. women was detected similarly by the iPod (32.5%), eGONI (29.5%), and peak GRF (30.9%). CONCLUSION: As measured with the iPod, mean rising power from the 5x STS is very reflective of a single maximal rep. The iPod is sufficiently sensitive to detect differences in chair rising power between sexes and can replace an electronic goniometer for assessing chair rising power.

Effects of Athletic Floor Surfaces on Cutting and Jumping Ground Reaction Forces in Female Athletes

PURPOSE: To assess ground reaction forces in female athletes performing sport-specific movements (drop vertical jump and cut) on two athletic flooring surfaces: Smartcells® [SM] and Sport Court® [SP], as compared with a control [CO] surface. METHODS: After providing informed consent, sixteen NCAA female athletes (age 20±1.3 yrs; height 175.8±7.3 cm; weight 71.5±7.1 kg) were instrumented with a standard lower extremity plug-in-gait marker set, after which ground reaction forces were assessed during performance of two movement types (drop vertical jump and 45 degree cut) on each surface using a 6 camera MOCAP system (Vicon, Denver, CO, USA) and two force platforms (AMTI, Watertown, MA, USA). Test order was randomized. Subjects performed 3 successful trials for each movement on each surface. Data were normalized by participant weight before comparison via paired t tests (p<0.05) between conditions for right-side peak and mean medial/lateral [ML], anterior/posterior [AP], and vertical [VERT] ground reaction forces [GRF]. RESULTS: During cutting, peak ML GRF for SM (42.62±15.31 N.kg-1) and SP (41.11±12.32 N.kg-1) were reduced as compared with CO (51.99±13.25 N.kg-1) (p=0.039 and p=0.002, respectively). Mean ML GRF for SM (4.14±4.28 N.kg-1) and SP (3.81±3.76 N.kg-1) were also reduced as compared with CO (6.58±5.18 N.kg-1) during cutting movements (p=0.009 and p=0.004, respectively). During drop vertical jump performance, mean AP GRF for both SM (-1.88±0.90 N.kg-1) and SP (-1.13±0.52 N.kg-1) were reduced as compared with CO (-4.02±1.33 N.kg-1) (p<0.0001 & p<0.0001, respectively). Peak ML GRF for SM (25.09±4.43 N.kg-1) was less than both CO (32.70±8.45 N.kg-1) (p=0.0009) and SP (29.67±5.36 N.kg-1) (p=0.0008). Mean ML GRF for SM (1.71±.33 N.kg-1) was less than CO (2.04±0.40 N.kg-1) (p=0.0012). Mean AP GRF for SP (-1.13±0.52) was reduced compared to SM (-1.88±0.90) (p=0.0011). A trend for peak VERT GRF between SM (151.99±5.28 N.kg-1) and both CO (156.91±10.71 N.kg-1) and SP (156.52±8.53 N.kg-1) during drop vertical jump was noted. CONCLUSION: SP and SM athletic flooring may reduce selected peak and mean GRF. SM mitigated GRF to a greater extent. Data trends also demonstrated reductions in VERT GRF during drop vertical jump for SM that may be further elucidated with a greater sample size in future efforts.

드롭 착지와 착지 후 점프 시 동적 자세 안정성 분석

This research aims to evaluate causes of injuries that could occur in the landing process, using the dynamic postural stability index (DPSI), by examining drop jumps and countermovement jumps in the experimental condition, thus exploring ways for injury prevention. For this research, a total of 22 male collage students (age: 23.1 ± 1.7 yrs, height: 177.0 ± 5.7 cm, weight: 69.2 ± 5.7 kg) joined the experiment. Items for the measurement included the front and rear, the left and right and vertical ground reaction forces using a force platform (2000 Hz). With measuring the above items, the study evaluated anterior-posterior stability index, mediolateral stability index, vertical stability index and dynamic postural stability index. The result showed that the peak anterior GRF and peak medial GRF, APSI, and %APSI were high in the drop jump, with the time for the peak vertical ground reaction force being delayed. In the case of countermovement jump, which is a sequence of actions, it showed that the peak posterior GRF, loading rate, VSI, DPSI and %VSI were high.

Scoliosis: lower limb asymmetries during the gait cycle.

BackgroundSeveral studies indicate that the gait pattern of subjects suffering from scoliosis differs from the norm. However, there is conflicting evidence regarding the source of this discrepancy.ObjectiveTo evaluate lower limb asymmetries in selected gait variables.Study designA case–control study on lower limb asymmetries during gait which can be related to scoliosis.Methods31 subjects with scoliosis (Study Group - SG) and an equal comparative control sample (Control Group – CG) of subjects underwent objective gait analysis with the Vicon® motion caption system whilst walking at a comfortable speed along the gait laboratory walkway. Analysis was performed at three levels: (1) Asymmetry in the SG against asymmetry in the CG, (2) Difference in magnitude of asymmetry between the SG and CG, and (3) Global mean values in the SG vs. CG. The Paired Student T-Test was used for intra-group analysis whilst the Independent Student T-Test was used for inter-group analysis of the selected parameters, which include temporal parameters (stride length, stride time, step length, individual step speed, speed of gait, cadence, swing-to-stance ratio), ground reaction force (peak GRF values during Loading and Propulsion phases, vertical component only) and electromyography (peak EMG values and their time of onset, as a percentage of the gait cycle) of two lower limb muscles (Gastronemius and Vastus Medialis).ResultsNo intra-group variation was found to be significant. However, the speed of gait was found to be significantly slower (p = 0.03) in scoliotic subjects when compared to the norm, as a result of the shorter stride length (p = 0.002 and longer stride time (p = 0.001) in the SG. Furthermore, there was statistical significance in the time of onset of EMG peaks for the Lateral Gastrocnemius (p = 0.02) with regards to inter-group difference in magnitude of lower limb asymmetry and global mean values.ConclusionsScoliosis is a tri-planar deformity which has some impact on the gait pattern. This research study concludes that scoliotic subjects have a slower speed of gait due to a shorter stride length and a longer stride time, together with variations in the timing of muscle activation.

Muscle optimization techniques impact the magnitude of calculated hip joint contact forces.

In musculoskeletal modelling, several optimization techniques are used to calculate muscle forces, which strongly influence resultant hip contact forces (HCF). The goal of this study was to calculate muscle forces using four different optimization techniques, i.e., two different static optimization techniques, computed muscle control (CMC) and the physiological inverse approach (PIA). We investigated their subsequent effects on HCFs during gait and sit to stand and found that at the first peak in gait at 15-20% of the gait cycle, CMC calculated the highest HCFs (median 3.9 times peak GRF (pGRF)). When comparing calculated HCFs to experimental HCFs reported in literature, the former were up to 238% larger. Both static optimization techniques produced lower HCFs (median 3.0 and 3.1 pGRF), while PIA included muscle dynamics without an excessive increase in HCF (median 3.2 pGRF). The increased HCFs in CMC were potentially caused by higher muscle forces resulting from co-contraction of agonists and antagonists around the hip. Alternatively, these higher HCFs may be caused by the slightly poorer tracking of the net joint moment by the muscle moments calculated by CMC. We conclude that the use of different optimization techniques affects calculated HCFs, and static optimization approached experimental values best.

The effects of functional activities on osteogenesis in the elderly

Objective To evaluate the osteogenic potential of selected exercises and determine which one has the greatest value for the elderly.Methods Twenty healthy old subjects were recruited in the study.Each subject performed the following four exercises in random order:stepping onto a 4-in riser (STEP),sit-to-stand (STS),jumping (JUMP) and marching (MARCH).The subjects performed successively each of the 4 exercises for 1 minute,with an interval of 3 minutes between each.The Vicon action capture system was used to record the peak ground reaction of the subjects during their exercises.The osteogenic index (OI) was calculated by the formula:OI=peak GRF/ (body weight×9.8) × In (number of loading cycles±1).Results JUMP and MARCH had superior OI value (7.52 ±2.06,6.51 ±1.59) than STEP (5.22 ±0.63) among the4 exercises (P＜0.05).STS was found to have the lowest OI (2.23 ± 0.42) in the elderly.There was no significant correlation between the height and OI in JUMP and MARCH (P ＞0.05).Conclusion STEP and MARCH had the higher OI value and could be deemed as the better ways to induce positive effects on bone health in the elderly population. Key words: Osteoporosis; Bone density; Loading exercise; Osteogenic index; The elderly

Contributions of the Soleus and Gastrocnemius muscles to the anterior cruciate ligament loading during single-leg landing

The aim of this study was to identify the contribution of the Soleus and Gastrocnemius (Gastroc) muscles' forces to anterior cruciate ligament (ACL) loading during single-leg landing. Although Quadriceps (Quads) and Hamstrings (Hams) muscles were recognized as the main contributors to the ACL loading, less is known regarding the role of ankle joint plantarflexors during landing. Eight healthy subjects performed single-landing tasks from 30 and 60cm heights. Scaled generic musculoskeletal models were developed in OpenSim to calculate lower limb muscle forces. The model consisted of 10 segments with 23 degrees of freedom and 92 lower body muscle-tendon units. Knee joint reaction forces were calculated based on the estimated muscle forces and used to predict ACL forces. We hypothesized that Soleus and Gastrocs muscle forces have opposite effects on tibial loading in the anterior/posterior directions. In situations where greater landing height would lead to an increase in GRF and risk of ACL injury, we further hypothesized that posterior forces of the Soleus and Hams would increase correspondingly to help protect the ACL during a safe landing maneuver. Our results demonstrated the antagonistic and agonistic roles of Gastrocs and Soleus respectively in ACL loading. The posterior force of Soleus reached 28–32% of Ham's posterior force for both landing heights at peak GRF while the posterior force of Gastrocs on femur was negligible. ACL injury risk during single-leg landing is not only dependent on knee musculature but also influenced by muscles that do not span the knee joint, such as the Soleus. In conclusion, the role of the ankle plantarflexors should be considered when developing training strategies for ACL injury prevention.

Leg stiffness can be maintained during reactive hopping despite modified acceleration conditions

AimThe aim of the present study was to evaluate reactive hops under systematically modified acceleration conditions. It was hypothesized that a high preactivity of the leg extensors and phase-specific adjustments of the leg muscle activation would compensate the alterations caused by the various acceleration levels in order to maintain a high leg stiffness, thus enabling the jumper to perform truly reactive jumps with short ground contact times despite the unaccustomed acceleration conditions. MethodsGround reaction forces (GRF), kinematic and electromyographic data of 20 healthy subjects were recorded during reactive hopping in a special sledge jump system for seven different acceleration levels: three acceleration levels with lower than normal gravity (0.7g, 0.8g, 0.9g), one with gravitational acceleration (1g) and three with higher acceleration (1.1g, 1.2g, 1.3g). ResultsThe increase of the acceleration from 0.7g to 1.3g had no significant effect on the preactivity of the leg extensors, the leg stiffness and the rate of force development. However, it resulted in increased peak GRF (+15%), longer ground contact time (+10%) and increased angular excursion at the ankle and knee joints (+3°). DiscussionThroughout a wide acceleration range, the subjects were able to maintain a high leg stiffness and perform reactive hops by keeping the preactivity constantly high and adjusting the muscle activity in the later phases. In consequence, it can be concluded that the neuromuscular system can cope with different acceleration levels, at least in the acceleration range used in this study.

착지의 높이와 거리가 무릎 부상 메카니즘에 미치는 영향

Various jumping and landing motions are shown during sports event. But most previous studies have not considered landing height and distance simultaneously. The purpose of this study was to identify the effects of landing height and distance on knee injury mechanism. Fourteen male(age: <TEX>$28.86{\pm}1.99$</TEX> yrs, height: <TEX>$177.00{\pm}4.69$</TEX> cm, weight: <TEX>$76.50{\pm}6.41$</TEX> kg) participated in this study. The subjects attempted drop landing task onto the ground from 30 cm to 45 cm heights and to 20 cm to 40 cm distances. The results were as follows. First, higher drop landing height and longer distance showed greater degree of maximal knee flexion and valgus. Second, higher drop landing height and longer distance showed greater maximal knee extension moment and varus moment. Third, higher drop landing height and longer distance showed larger maximal knee absorption power. Lastly, higher drop landing height showed increased Peak GRF. Landing height was more related to the cause of injury, which was indicated by increased maximal knee extension moment, peak GRF and maximal knee absorption power. Landing distance was also associated with increased knee valgus moment and absorption power during landing. These results suggest that landing height and distance may be the cause of injury.

Plantar Pressure During Running in Subjects With Chronic Ankle Instability

It has been suggested that dynamic foot and ankle mechanics predispose individuals with CAI to repetitive episodes of the ankle ``giving way.'' Plantar pressure variations during a walking gait have been detected in those with CAI, but more dynamic conditions for analysis are needed. The purpose of this study was to evaluate plantar pressure distributions during a running gait in individuals with CAI, individuals who suffered a lateral ankle sprain, but did not develop CAI (AS), and subjects with no history of a lateral ankle sprain (CON). Forty-five subjects [15 in each group, healthy males (18) and females (27), age 18 to 45] were recruited from University communities to participate in this study. Plantar pressure distributions were analyzed on a Tekscan© plantar pressure mat at 66 frames per second during a running gait at a controlled speed. The following variables were obtained: rearfoot medial/lateral (M/L) pressure ratio at foot strike (FS) and center-of-pressure (COP) trajectory during the initial loading response (heel strike to initial peak GRF). Separate one-way ANOVA with Tukey's post-hoc were used to test for group differences. The significance level was defined as p < 0.05. The CAI group had a significantly more lateral ratio (0.97 ± 0.12) at FS when compared to the CON (1.01 ± 0.13) and AS (1.11 ± 0.13) groups. The CAI subjects had a lateral COP trajectory during the loading phase (7.97 degrees ± 11.02), while both the AS (-3.68 degrees ± 10.24) and CON groups (-6.27 degrees ± 9.86) had medial trajectories. The difference was significant between the CAI group and both the AS and CON groups (all significant {\it p} values were less than 0.05). Our results confirm that CAI subjects have a more lateral foot positioning and loading pattern during a barefoot running gait when compared to both the CON and LAS groups. Clinicians treating patients with CAI should consider providing interventions to decrease the amount of rearfoot inversion at FS and during loading in order to create a more medial COP trajectory upon impact.