Lower extremity control and dynamics during backward angular impulse generation in forward translating tasks

Observation of complex whole body movements suggests that the nervous system coordinates multiple operational subsystems using some type of hierarchical control. When comparing two forward translating tasks performed with and without backward angular impulse, we have learned that both trunk-leg coordination and reaction force-time characteristics are significantly different between tasks. This led us to hypothesize that differences in trunk-leg coordination and reaction force generation would induce between-task differences in the control of the lower extremity joints during impulse generation phase of the tasks. Eight highly skilled performers executed a series of forward jumps with and without backward rotation (reverse somersault and reverse timer, respectively). Sagittal plane kinematics, reaction forces, and electromyograms of lower extremity muscles were acquired during the take-off phase of both tasks. Lower extremity joint kinetics were calculated using inverse dynamics. The results demonstrated between-task differences in the relative angles between the lower extremity segments and the net joint forces/reaction force and the joint angular velocity profiles. Significantly less knee extensor net joint moments and net joint moment work and greater hip extensor net joint moments and net joint moment work were observed during the push interval of the reverse somersault as compared to the reverse timer. Between-task differences in lower extremity joint kinetics were regulated by selectively activating the bi-articular muscles crossing the knee and hip. These results indicate that between-task differences in the control of the center of mass relative to the reaction force alters control and dynamics of the multijoint lower extremity subsystem.     

The effect of falling height on muscle activity and foot motion during landings

The aims of this study were: (a) to examine the effect of falling height on the kinematics of the tibiotalar, talonavicular and calcaneocuboid joints and (b) to study the influence of falling height on the muscle activity of the leg during landings. Six female gymnasts (height: 1.63±0.04 m, weight: 58.21±3.46 kg) participated in this study. All six gymnasts carried out barefoot landings, falling from 1.0, 1.5 and 2.0 m height onto a mat. Three genlocked digital high speed video cameras (250 Hz) captured the motion of the left shank and foot. Surface electromyography (EMG) was used to measure muscle activity (1000 Hz) from five muscles (gastrocnemius medialis, tibialis anterior, peroneus longus, vastus lateralis and hamstrings) of the left leg. The kinematics of the tibiotalar, talonavicular and calcaneocuboid joints were studied. The lower-leg and the foot were modelled by means of a multi-body system, comprising seven rigid bodies. The falling height does not show any influence on the kinematics neither of the tibiotalar nor of the talonavicular joints during landing. The eversion at the calcaneocuboid joint increases with increasing falling height. When augmenting falling height, the myoelectric activity of the muscles of the lower limb increases as well during the pre-activation phase as during the landing itself. The muscles of the lower extremities are capable of stabilizing the tibiotalar and the talonavicular joints actively, restricting their maximal motion by means of a higher activation before and after touchdown. Maximal eversion at the calcaneocuboid joint increases about 52% when landing from 2.0 m.     

A subsequent movement alters lower extremity muscle activity and kinetics in drop jumps vs. drop landings

Drop landings and drop jumps are common training exercises and injury research model tasks. Drop landings have a single landing, whereas drop jumps include a subsequent jump after initial landing. With the expected ground impact, instant and landing surface suggested to modulate landing neuromechanics, muscle activity, and kinetics should be the same in both tasks when landing from the same height onto the same surface. Although previous researchers have noted some differences between these tasks across separate studies, little research has compared these tasks in the same study. Thus, we examined whether a subsequent movement after initial landing alters muscle activity and kinetics between drop landings and jumps. Fifteen women performed 10 drop landings and drop jumps each from 45 cm. Muscle onsets and integrated muscle activation amplitudes 150 milliseconds before (preactivity) and after landing (postactivity) in the medial and lateral quadriceps, hamstrings, and lateral gastrocnemius and peak and time-to-peak vertical ground reaction forces were examined across tasks (p ≤ 0.05). When performing drop jumps, subjects demonstrated later (p = 0.02) gastrocnemius and lesser lateral gastrocnemius (p = 0.002) and medial quadriceps (p = 0.02) preactivity followed by increased postactivity in all muscles (p = 0.006), with higher peak vertical ground reaction forces (p = 0.04) but no differences in times to these peaks (p = 0.60) than drop landings. The later gastrocnemius activation, higher gastrocnemius and quadriceps postlanding amplitudes, and higher ground reaction forces in drop jumps may allow subjects to propel the body vertically after the initial landing vs. simply absorbing impact in drop landings. Our results indicate that in addition to landing surface and height, anticipation of a subsequent task changes landing neuromechanics. Generalizations of results from landing-only studies should not be made with landing followed-by-subsequent-activity studies. Landing exercises should be incorporated based on sport-specific demands.     

Lower extremity joint kinetic responses to external resistance variations

The purpose of this investigation was to determine if increases in external resistance during a squat movement would be controlled by proportionally scaling the net joint moment work or average net joint moment (NJM) at the hip, knee, and ankle. Eighteen experienced subjects performed 3 sets of 3 repetitions each of a squat movement using resistances of 25, 50, 75, and 100% of their 3-repetition maximum, while instrumented for biomechanical analyses. Standard inverse dynamics techniques and numerical integration were used to calculate the NJM work and average NJM of each joint. A combination of single-subject and group mean statistical analyses indicated that the neither the NJM work nor average NJM increased proportionately in response to increases in external loading. Results suggest a complex control strategy in which the hip was the dominant contributor, increased linearly with the external load, and had low variability. The knee and ankle contributions were neither as great nor as linear, and were highly variable, suggesting that they were influenced by more than just the external load. The disproportionate response of each joint to varying external resistances suggests that controlling the force output of multijoint chains requires further study and modifications to existing motor control theories.     

Coordination of lower extremity multi-joint control strategies during the golf swing

This study aimed to understand how players coordinate the multi-joint control strategies of the rear and target legs to satisfy the lower extremity and whole-body mechanical objectives during the golf swing when hitting shots with different clubs. Highly skilled golf players (n = 10) performed golf swings with a 6-iron and a driver. Joint kinetics were calculated using ground reaction forces and segment kinematics to determine net joint moments (NJMs) during the interval of interest within the downswing. Between club difference in NJMs and 3D support moments were compared across the group and within a player. Although player-specific multi-joint control strategies arose, players generally increased target leg ankle, knee, and hip NJMs when hitting with the driver while maintaining the relative contribution to the 3D support moment. Multi-joint control strategies used to control the target and rear legs were found to be different, yet the majority of the 3D support moment was produced by NJMs about an axis perpendicular to the leg planes. These results emphasize the importance of recognizing how an individual player coordinates multi-joint control from each leg, and highlights the need to design interventions that are player and leg specific to aid in improving player performance.     

The effects of single-leg landing technique on ACL loading

Anterior Cruciate Ligament (ACL) injury is one of the most serious and costly injuries of the lower extremity, occurring more frequently in females than males. Injury prevention training programs have reported the ability to reduce non-contact ACL injury occurrence. These programs have also been shown to alter an athletes' lower extremity position at initial contact with the ground and throughout the deceleration phase of landing. The purpose of this study was to determine the influence of single-leg landing technique on ACL loading in recreationally active females. Participants were asked to perform "soft" and "stiff" drop landings. A series of musculoskeletal models were then used to estimate muscle, joint, and ACL forces. Dependent t-tests were conducted to investigate differences between the two landing techniques (p<0.05). Instructing participants to land 'softly' resulted in a significant decrease in peak ACL force (p=0.05), and a significant increase in hip and knee flexion both at initial contact (IC) and the time of peak ACL force (F(PACL)). These findings suggest that altering landing technique using simple verbal instruction may result in lower extremity alignment that decreases the resultant load on the ACL. Along with supporting the findings of reduced ACL force with alterations in sagittal plane landing mechanics in the current literature, the results of this study suggest that simple verbal instruction may reduce the ACL force experienced by athletes when landing.     

Modification of landing conditions at contact via flight

Weight-bearing tasks performed by humans consist of a series of phases with multiple objectives. Analysis of the relationship between control and dynamics during successive phases of the tasks is essential for improving performance without sustaining injury. Experimental evidence regarding foot landings suggests that the distribution of momentum among segments at contact influences stability during interaction with the landing surface. In this study, we hypothesized that modification of control in one subsystem, in our case shoulder torque, during the flight phase of an aerial task would enable the performer to maintain behavior of other subsystems (e.g.lower extremity kinematics) and initiate contact with momentum conditions consistent with successful task performance. To test this hypothesis, an experimentally validated multilink dynamic model that incorporated modifications in shoulder torque was used to simulate the flight phase dynamics of overrotated landings. The simulation results indicate that modification in shoulder torque during the flight phase enables gymnasts to maintain lower extremity kinematics and initiate contact with trunk angular velocities consistent with those observed during successful landings. These results suggest that modifications in the control logic of one subsystem may be sufficient for achieving both global and local task objectives of landing.     

Landing from different heights: Biomechanical and neuromuscular strategies in trained gymnasts and untrained prepubescent girls

The purpose of this study was to examine the biomechanics of the lower limb, during landing in female prepubertal gymnasts and prepubertal untrained girls, aged 9–12 years. Ten healthy participants were included in each group and performed five landings from 20, 40, and 60 cm. Kinematics, ground reaction forces (GRF) and electromyogram (EMG) from the lateral gastrocnemius, tibialis anterior, and vastus lateralis are presented. Gymnasts had higher vertical GRF and shorter braking phase during landing. Compared to untrained girls, gymnasts exhibited for all examined drop heights more knee flexion before and at ground contact, but less knee flexion at maximum knee flexion position. Especially when increasing drop heights the gymnasts activated their examined muscles earlier, and generally they had higher pre- and post landing EMG amplitudes normalized to the peak EMG at 60 cm drop height. Furthermore, gymnasts had lower antagonist EMG for the tibialis anterior compared to untrained girls, especially when landing from higher heights. It is concluded that the landing strategy preferred by gymnasts is influenced by long-term and specialized training and induces a stiffer landing pattern. This could have implications in injury prevention, which requires further investigation.     

LANDING QUALITY IN ARTISTIC GYMNASTICS IS RELATED TO LANDING SYMMETRY

In gymnastics every exercise finishes with a landing. The quality of landing depends on subjective (e.g. biomechanical) and objective (e.g. mechanical characteristics of landing area) factors. The aim of our research was to determine which biomechanical (temporal, kinematic and dynamic) characteristics of landing best predict the quality of landing. Twelve male gymnasts performed a stretched forward and backward salto; also with 1/2, 1/1 and 3/2 turns. Stepwise multiple regression extracted five predictors which explained 51.5% of landing quality variance. All predictors were defining asymmetries between legs (velocities, angles). To avoid asymmetric landings, gymnasts need to develop enough height; they need higher angular momentum around the transverse and longitudinal axis and they need to better control angular velocity in the longitudinal axis.     

The mechanical consequences of dynamic frontal plane limb alignment for non-contact ACL injury

This study investigated the mechanical consequences of differences in dynamic frontal plane alignment of the support limb and the influence of anticipatory muscle activation at the hip and ankle on reducing the potential for non-contact ACL injury during single-limb landing. A frontal plane, three-link passive dynamic model was used to estimate an ACL non-contact injury threshold. This threshold was defined as the maximum axial force that the knee could sustain before the joint opened 8 degrees either medially or laterally, which was deemed sufficient to cause injury. The limb alignment and hip and ankle muscle contractions were varied to determine their effects on the ACL injury threshold. Valgus or varus alignment reduced the injury threshold compared to neutral alignment, but increasing the anticipatory contraction of hip abduction and adduction muscle groups increased the injury threshold. Increasing anticipatory ankle inversion/eversion muscle contraction had no effect. This study provides a mechanical rationale for the conclusion that a neutral limb alignment (compared to valgus or varus) during landing and increasing hip muscle contraction (abductors/adductors) prior to landing can reduce the possibility of ACL rupture through a valgus or varus opening mechanism.     

Effect of fatigue on single-leg hop landing biomechanics

The objective of this study was to measure adaptations in landing strategy during single-leg hops following thigh muscle fatigue. Kinetic, kinematic, and electromyographic data were recorded as thirteen healthy male subjects performed a single-leg hop in both the unfatigued and fatigued states. To sufficiently fatigue the thigh muscles, subjects performed at least two sets of 50 step-ups. Fatigue was assessed by measuring horizontal hopping ability following the protocol. Joint motion and loading, as well as muscle activation patterns, were compared between fatigued and unfatigued conditions. Fatigue significantly increased knee motion (p = 0.012) and shifted the ankle into a more dorsiflexed position (p = 0.029). Hip flexion was also reduced following fatigue (p = 0.042). Peak extension moment tended to decrease at the knee and increase at the ankle and hip (p = 0.014). Ankle plantar flexion moment at the time of peak total support moment increased from 0.8 (N x m)/kg (SD, 0.6 [N x m]/kg) to 1.5 (N x m)/kg (SD, 0.8 [N x m]/kg) (p = 0.006). Decreased knee moment and increased knee flexion during landings following fatigue indicated that the control of knee motion was compromised despite increased activation of the vastus medialis, vastus lateralis, and rectus femoris (p = 0.014, p = 0.014, and p = 0.017, respectively). Performance at the ankle increased to compensate for weakness in the knee musculature and to maintain lower extremity stability during landing. Investigating the biomechanical adaptations that occur in healthy subjects as a result of muscle fatigue may give insight into the compensatory mechanisms and loading patterns occurring in patients with knee pathology. Changes in single-leg hop landing performance could be used to demonstrate functional improvement in patients due to training or physical therapy.     

The influence of simulation model complexity on the estimation of internal loading in gymnastics landings

Evaluating landing technique using a computer simulation model of a gymnast and landing mat could be a useful tool when attempting to assess injury risk. The aims of this study were: (1) to investigate whether a subject-specific torque-driven or a subject-specific muscle-driven model of a gymnast is better at matching experimental ground reaction forces and kinematics during gymnastics landings, (2) to calculate their respective simulation run times and (3) to determine what level of model complexity is required to assess injury risk. A subject-specific planar seven-link wobbling mass model of a gymnast and a multi-layer model of a landing mat were developed for this study. Subject-specific strength parameters were determined which defined the maximum voluntary torque/angle/angular velocity relationship about each joint. This relationship was also used to produce subject-specific 'lumped' muscle models for each joint. Kinetic and kinematic data were obtained during landings from backward and forward rotating gymnastics vaults. Both torque-driven and muscle-driven models were capable of producing simulated landings that matched the actual performances (with overall percentage differences between 10.1% and 18.2%). The torque-driven model underestimated the internal loading on joints and bones, resulting in joint reaction forces that were less than 50% of those calculated using the muscle-driven model. Simulation time increased from approximately 3 min (torque driven) to more than 10 min (muscle driven) as model complexity increased. The selection of a simulation model for assessing injury risk must consider the need for determining realistic internal forces as the priority despite increases in simulation run time.     

Lower extremity function in terms of shock absorption when landing with unsynchronized feet

The purpose of this study was to clarify the lower extremity function in terms of the shock absorption during unsynchronized-foot landings. The characteristics of the supination and pronation in the ankle joint at landing were investigated, assuming that the measurements of the impact force on the body could be demonstrated by the changes that occurred during 3 different landing motions: -unsynchronized-foot landings, synchronized-foot landings, and one-foot landings. Subjects jumped to the floor from 10-cm footstools 3 times for each type of landing. For the synchronized-foot landing, the rear foot angle was 92.2 degrees at the start of landing and did not change significantly from landing start to 100 msec. For the one-foot landing, rear foot angle was 95.1 degrees at the start of landing and decreased rapidly to 87.1 degrees by 75 msec, and then increased rapidly to 90.8 degrees by 140 msec. For the unsynchronized-foot landing, the rear foot angle was 93.8 degrees at the start of the landing, decreased rapidly to 88.0 degrees by 75 msec, and then increased rapidly to 89.9 degrees by 115 msec.It was clarified that the lower extremity function for the shock attenuation during landing with the unsynchronized-foot was similar to that with one-foot landings, and the lower extremity function for supporting the body after another foot landing was similar to that after the synchronized-foot landings in this study.     

Gender comparisons between unilateral and bilateral landings

The increased number of women participating in sports has led to a higher knee injury rate in women compared with men. Among these injuries, those occurring to the ACL are commonly observed during landing maneuvers. The purpose of this study was to determine gender differences in landing strategies during unilateral and bilateral landings. Sixteen male and 17 female recreational athletes were recruited to perform unilateral and bilateral landings from a raised platform, scaled to match their individual jumping abilities. Three-dimensional kinematics and kinetics of the dominant leg were calculated during the landing phase and reported as initial ground contact angle, ranges of motion (ROM) and peak moments. Lower extremity energy absorption was also calculated for the duration of the landing phase. Results showed that gender differences were only observed in sagittal plane hip and knee ROM, potentially due to the use of a relative drop height versus the commonly used absolute drop height. Unilateral landings were characterized by significant differences in hip and knee kinematics that have been linked to increased injury risk and would best be classified as "stiff" landings. The ankle musculature was used more for impact absorption during unilateral landing, which required increased joint extension at touchdown and may increase injury risk during an unbalanced landing. In addition, there was only an 11% increase in total energy absorption during unilateral landings, suggesting that there was a substantial amount of passive energy transfer during unilateral landings.     

The effects of floor incline on lower extremity biomechanics during unilateral landing from a jump in dancers

Retrospective studies have suggested that dancers performing on inclined ("raked") stages have increased injury risk. One study suggests that biomechanical differences exist between flat and inclined surfaces during bilateral landings; however, no studies have examined whether such differences exist during unilateral landings. In addition, little is known regarding potential gender differences in landing mechanics of dancers. Professional dancers (N = 41; 14 male, 27 female) performed unilateral drop jumps from a 30 cm platform onto flat and inclined surfaces while extremity joint angles and moments were identified and analyzed. There were significant joint angle and moment effects due to the inclined flooring. Women had significantly decreased peak ankle dorsiflexion and hip adduction moment compared with men. Findings of the current study suggest that unilateral landings on inclined stages create measurable changes in lower extremity biomechanical variables. These findings provide a preliminary biomechanical rationale for differences in injury rates found in observational studies of raked stages.     

Coordinate activity of the quadratus lumborum posterior layer,lumbar multifidus,erector spinae,and gluteus medius during single-leg forward landing

This study aimed to clarify the differences in electromyographic activity between the quadratus lumborum anterior (QL-a) and posterior layers (QL-p), and the relationship among trunk muscles and gluteus medius (GMed) activities during forward landing. Thirteen healthy men performed double-leg and single-leg (ipsilateral or contralateral sides as the electromyography measurement of trunk muscles) forward landings from a 30 cm-height-box. The onset of electromyographic activity in pre-landing and the electromyographic amplitude of the unilateral QL-a, QL-p, abdominal muscles, lumbar multifidus (LMF), erector spinae (LES), and bilateral GMed were recorded. Two-way ANOVA was used to compare the onset of electromyographic activity (3 landing leg conditions × 10 muscles) and electromyographic amplitude among (3 landing leg conditions × 2 phases). The onset of QL-p was significantly earlier in contralateral-leg landing than in the double-leg and ipsilateral-leg landings. The onset of LMF and LES was significantly earlier than that of the abdominal muscles in contralateral-leg landing. QL-p activity and GMed activity on the contralateral leg side in the pre-landing were significantly higher in contralateral-leg landing than in the other leg landings. To prepare for pelvic and trunk movements after ground contact, LMF, LES, QL-p on non-support leg side, and GMed on support leg side showed early or high feedforward activation before ground contact during single-leg forward landing.     

Reducing ground reaction forces in gymnastics’ landings may increase internal loading

The aim of this study was to use a subject-specific seven-link wobbling mass model of a gymnast, and a multi-layer model of a landing mat, to determine landing strategies that minimise ground reaction forces (GRF) and internal forces. Subject-specific strength parameters were determined that defined the maximum voluntary torque/angle/angular velocity relationship at each joint. These relationships were used to produce subject-specific ‘lumped’ linear muscle models for each joint. Muscle activation histories were optimised using a Simplex algorithm to minimise GRF or bone bending moments for forward and backward rotating vault landings. Optimising the landing strategy to minimise each of the GRF reduced the peak vertical and horizontal GRF by 9% for the backward rotating vault and by 8% and 48% for the forward rotating vault, compared to a matching simulation. However, most internal loading measures (bone bending moments, joint reaction forces and muscle forces) increased compared to the matching simulation. Optimising the landing strategy to minimise the peak bone bending moments resulted in reduced internal loading measures, and in most cases reduced GRF. Bone bending moments were reduced by 27% during the forward rotating vault and by 2% during the backward rotating vault landings when compared to the matching simulations. It is possible for a gymnast to modify their landing strategy in order to minimise internal forces and lower GRF. However, using a reduction in GRF, due to a change in landing strategy, as a basis for a reduction in injury potential in vaulting movements may not be appropriate since internal loading can increase.     

The Roles of Monoarticular and Biarticular Muscles of the Lower Limbs in Terrestrial Locomotion

Specific features of the functioning of mono- and biarticular muscles were studied using a multijoint movement (a high jump) as an example. The powers of the knee and ankle joint extensors are insufficient for a strong and quick movement such as a high jump. Biarticular muscles (m. rectus femoris) transfer forces/powers from one joint to another, thereby compensating for the physiological shortcoming of monoarticular muscles, that is, a decrease in the tractive force with increasing contraction rate. In a high jump, a power of 300 W may be transferred from the hip to the knee joint via the m. rectus femoris; 230 W, from the knee to the hip joint via the hamstring muscle; 210 W, from the knee joint to the ankle via the m. gastrocnemius; and 15 W, from the metatarsophalangeal joint to the ankle via the mm. flexors.     

Effects of various midsole densities of basketball shoes on impact attenuation during landing activities

The purpose of this study was to examine effects of shoe midsole densities and mechanical demands (landing heights) on impact shock attenuation and lower extremity biomechanics during a landing activity. Nine healthy male college athletes performed 5 trials of step-off landing in each of 9 test conditions, i.e., a combination of landings in shoes of 3 midsole densities (soft, normal, hard) from each of 3 landing potential energy (PE) levels (low, median, high). Ground reaction forces (GRF), accelerations (ACC) of the tibia and forehead, and sagittal kinematic data were sampled simultaneously. A 3 x 3 two-way (surface x height) repeated-measures analysis of variance (ANOVA) was performed on selected kinematic, ACC, and GRF variables; a 3 x 3 x 3 three-way (surface x height x joint) ANOVA was performed on variables related to eccentric muscular work. The GRF results showed that the forefoot peak GRF in the normal and hard midsoles was significantly greater than the soft midsole at the low and median PEs. Rearfoot peak GRF was significantly greater for the hard midsole than for the soft and normal midsoles at the median and high PEs, respectively. The peak head and tibia peak ACC were also attenuated in similar fashion. Kinematic variables did not vary significantly across different midsoles, nor did energy absorbed through lower extremity extensors in response to the increased shoe stiffness. Knee joint extensors were shown to be dominant in attenuating the forefoot impact force across the landing heights. The results showed limited evidence of impact-attenuating benefits of the soft midsole in the basketball shoes.     

Lower extremity extension force and electromyography properties as a function of knee angle and their relation to joint torques: implications for strength diagnostics

The purpose of this study was to evaluate whether and how isometric multijoint leg extension strength can be used to assess athletes' muscular capability within the scope of strength diagnosis. External reaction forces (Fext) and kinematics were measured (n = 18) during maximal isometric contractions in a seated leg press at 8 distinct joint angle configurations ranging from 30 to 100° knee flexion. In addition, muscle activation of rectus femoris, vastus medialis, biceps femoris c.l., gastrocnemius medialis, and tibialis anterior was obtained using surface electromyography (EMG). Joint torques for hip, knee, and ankle joints were computed by inverse dynamics. The results showed that unilateral Fext decreased significantly from 3,369 ± 575 N at 30° knee flexion to 1,015 ± 152 N at 100° knee flexion. Despite maximum voluntary effort, excitation of all muscles as measured by EMG root mean square changed with knee flexion angles. Moreover, correlations showed that above-average Fext at low knee flexion is not necessarily associated with above-average Fext at great knee flexion and vice versa. Similarly, it is not possible to deduce high joint torques from high Fext just as above-average joint torques in 1 joint do not signify above-average torques in another joint. From these findings, it is concluded that an evaluation of muscular capability by means of Fext as measured for multijoint leg extension is strongly limited. As practical recommendation, we suggest analyzing multijoint leg extension strength at 3 distinct knee flexion angles or at discipline-specific joint angles. In addition, a careful evaluation of muscular capacity based on measured Fext can be done for knee flexion angles ≥ 80°. For further and detailed analysis of single muscle groups, the use of inverse dynamic modeling is recommended.