Joint Torque and Mechanical Power of Lower Extremity and Its Relevance to Hamstring Strain during Sprint Running

The effect of motor experience on knee stability and inter-joint coordination when cutting at different angles

BACKGROUND

Most studies on cutting have focused on the biomechanics of the knee and lower-limb muscle activation characteristics, with less consideration given to the influence of motor experience on control strategies at the joint level. This study aimed to investigate the differences in knee stability and inter-joint coordination between high- and low-level athletes when cutting at different angles.

METHODS

A Vicon motion capture system and a Kistler force table were used to obtain kinematic and ground reaction force data during cutting. Joint dynamic stiffness and vector coding were used to assess knee stability and inter-joint coordination. Uncontrolled manifold analysis was used to clarify whether there was synergy among lower-limb joints to maintain postural stability during cutting.

RESULTS

During the load acceptance phase, skilled subjects had the smallest joint stiffness at 90° compared with novice subjects (P < 0.05). Compared with novice subjects, skilled subjects had smaller knee-hip ellipse areas at 90° and 135° (P < 0.05), but larger knee-ankle ellipse areas at 135° (P < 0.05). The synergy index in load acceptance was significantly higher (P < 0.05) for skilled subjects at 90° and 135°.

CONCLUSIONS

Advanced subjects can adjust joint control strategies to adapt to the demands of large-angle cutting on the change of direction. Advanced subjects can reduce knee stability for greater flexibility during cutting compared with novice subjects. By increasing the degree of synergy among the lower-limb joints, advanced athletes can maintain high postural stability.

Ankle and Plantar Flexor Muscle-Tendon Unit Function in Sprinters: A Narrative Review

Maximal sprinting in humans requires the contribution of various muscle-tendon units (MTUs) and joints to maximize performance. The plantar flexor MTU and ankle joint are of particular importance due to their role in applying force to the ground. This narrative review examines the contribution of the ankle joint and plantar flexor MTUs across the phases of sprinting (start, acceleration, and maximum velocity), alongside the musculotendinous properties that contribute to improved plantar flexor MTU performance. For the sprint start, the rear leg ankle joint appears to be a particularly important contributor to sprint start performance, alongside the stretch-shortening cycle (SSC) action of the plantar flexor MTU. Comparing elite and sub-elite sprinters revealed that elite sprinters had a higher rate of force development (RFD) and normalized average horizontal block power, which was transferred via the ankle joint to the block. For the acceleration phase, the ankle joint and plantar flexor MTU appear to be the most critical of the major lower limb joints/MTUs. The contribution of the ankle joint to power generation and positive work is minimal during the first stance, but an increased contribution is observed during the second stance, mid-acceleration, and late-acceleration. In terms of muscular contributions, the gastrocnemius and soleus have distinct roles. The soleus acts mainly as a supporter, generating large portions of the upward impulse, whereas the gastrocnemius acts as both an accelerator and a supporter, contributing significantly to propulsive and upward impulses. During maximum velocity sprinting the ankle joint is a net dissipater of energy, potentially due to the greater vertical loading placed on the plantar flexors. However, the ankle joint is critical for energy transfer from proximal joints to ground force application to maintain velocity. In terms of the contribution of musculoskeletal factors to ankle joint and plantar flexor performance, an optimal plantar flexor MTU profile potentially exists, which is possibly a combination of several musculoskeletal factors, alongside factors such as footwear and technique.

Ankle Muscle Activations during Different Foot-Strike Patterns in Running

This study analysed the landing performance and muscle activity of athletes in forefoot strike (FFS) and rearfoot strike (RFS) patterns. Ten male college participants were asked to perform two foot strikes patterns, each at a running speed of 6 km/h. Three inertial sensors and five EMG sensors as well as one 24 G accelerometer were synchronised to acquire joint kinematics parameters as well as muscle activation, respectively. In both the FFS and RFS patterns, according to the intraclass correlation coefficient, excellent reliability was found for landing performance and muscle activation. Paired t tests indicated significantly higher ankle plantar flexion in the FFS pattern. Moreover, biceps femoris (BF) and gastrocnemius medialis (GM) activation increased in the pre-stance phase of the FFS compared with that of RFS. The FFS pattern had significantly decreased tibialis anterior (TA) muscle activity compared with the RFS pattern during the pre-stance phase. The results demonstrated that the ankle strategy focused on controlling the foot strike pattern. The influence of the FFS pattern on muscle activity likely indicates that an athlete can increase both BF and GM muscles activity. Altered landing strategy in cases of FFS pattern may contribute both to the running efficiency and muscle activation of the lower extremity. Therefore, neuromuscular training and education are required to enable activation in dynamic running tasks.

Effects of Short-Term Limitation of Movement of the First Metatarsophalangeal Joint on the Biomechanics of the Ipsilateral Hip, Knee, and Ankle Joints During Walking

BACKGROUND We analyzed the effect of limitation of movement of the first metatarsophalangeal joint (FMJ) on the biomechanics of the lower limbs during walking. MATERIAL AND METHODS Eight healthy college students completed walking under barefoot (BF) and FMJ constraint (FMJC) conditions. We synchronously collected kinematics and dynamics data, and calculated the torque, power, and work of hip, knee, and ankle joints. RESULTS Compared with normal conditions, when the FMJ is restricted from walking, the maximum ankle dorsiflexion angle is significantly increased (P<0.001), the maximum plantar flexion angle is significantly reduced (P<0.001), the maximum plantar flexion torque (P<0.001) and the maximum dorsiflexion torque (P<0.05) increased significantly, the maximum power increased significantly (P<0.001), the minimum power decreased significantly (P<0.001), and the negative work increased significantly (P<0.001). The torque of hip and knee joints increased significantly (P<0.05). CONCLUSIONS After the movement of the FMJ is restricted, the human body mainly compensates and transfers compensation by increasing the angle of dorsiflexion, increasing work and the activity level of surrounding muscles through the ankle joint, thereby increasing the torque load of the knee and hip joints to maintain the dynamic balance of kinematics. FMJC condition increases the energy consumption of the human ankle, knee, and hip joints during walking. The load is compensated by the gradual attenuation of the ankle, knee, and hip. Long-term limitation may cause damage to the posterior calf muscles and increase the incidence of knee arthritis.

Human Lower Limb Joint Biomechanics in Daily Life Activities: A Literature Based Requirement Analysis for Anthropomorphic Robot Design

Daily human activity is characterized by a broad variety of movement tasks. This work summarizes the sagittal hip, knee, and ankle joint biomechanics for a broad range of daily movements, based on previously published literature, to identify requirements for robotic design. Maximum joint power, moment, angular velocity, and angular acceleration, as well as the movement-related range of motion and the mean absolute power were extracted, compared, and analyzed for essential and sportive movement tasks. We found that the full human range of motion is required to mimic human like performance and versatility. In general, sportive movements were found to exhibit the highest joint requirements in angular velocity, angular acceleration, moment, power, and mean absolute power. However, at the hip, essential movements, such as recovery, had comparable or even higher requirements. Further, we found that the moment and power demands were generally higher in stance, while the angular velocity and angular acceleration were mostly higher or equal in swing compared to stance for locomotion tasks. The extracted requirements provide a novel comprehensive overview that can help with the dimensioning of actuators enabling tailored assistance or rehabilitation for wearable lower limb robots, and to achieve essential, sportive or augmented performances that exceed natural human capabilities with humanoid robots.

Acute effects of wearable thigh and shank loading on spatiotemporal and kinematic variables during maximum velocity sprinting

Light wearable resistance is used in sprint training but the scientific evidence to guide its implementation is limited. This study investigated thigh and shank loading protocols which were matched based on the average increase in moment of inertia about the hip over a stride cycle. Seven university-level sprinters completed three counterbalanced conditions (unloaded, shank-loaded, thigh-loaded), and kinematic variables were measured between 30 and 40 m. Both thigh and shank loading led to small reductions in step velocity (mean change = -1.4% and -1.2%, respectively). This was due to small reductions in step frequency (-1.8%; -1.7%) because of small increases in contact time (+2.7%; +1.5%) in both conditions and a small increase in flight time (+2.0%) in the shank-loaded condition. Both conditions led to moderate increases in hip extension at toe-off (+2.7°; +1.4°), whilst thigh loading led to a small reduction in peak hip flexion angle during swing (-2.5°) and shank loading led to a small increase in peak biceps femoris muscle-tendon unit length (+0.4%). Thigh and shank loading can both be used to provide small reductions in sprint velocity, and each has specific overload effects which must be considered in the rationale for their implementation.

Integrated System for Monitoring Muscular States during Elbow Flexor Resistance Training in Bedridden Patients

To improve or maintain the physical function of bedridden patients, appropriate and effective exercises are required during the patient's bed rest. Resistance training (RT) is an effective exercise for improving the physical function of bedridden patients, and the improvement of the physical function is caused by mechanical stimuli associated with RT. Currently, the measured mechanical stimuli are external variables which represent the synthetic effect of multiple muscles and body movements. Important features of stimuli experienced by muscles are of crucial importance in explaining muscular strength and power adaptation. This study describes an integrated system for assessing muscular states during elbow flexor resistance training in bedridden patients, and some experiments were carried out to test and evaluate this system. The integrated system incorporates an elbow joint angle estimation model (EJAEM), a musculoskeletal model (MSM), and a muscle-tendon model. The EJAEM enables real-time interaction between patient and MSM. The MSM is a three-dimensional model of the upper extremity, including major muscles that make up the elbow flexor and extensor, and was built based on public data. One set of concentric and eccentric contraction was performed by a healthy subject, and the results of the calculations were analyzed to show important features of mechanical stimuli experienced by muscles during the training. The integrated system provides a considerable method to monitor the body-level and muscle-level mechanical stimuli during elbow flexor resistance training in bedridden patients.