Wrist Torque Research Articles

Dynamic balance of circles with one support point on pommel horse exercise

Double-leg circles on pommel horse exercises require a high degree of dynamic balance. However, theoretical conditions for maintaining dynamic balance are unclear. The purpose of this paper is to propose a simple theoretical model of the dynamic balance of the circles, and to illustrate its qualitative properties. To this end, the body of a gymnast is simply modeled as one rigid body with one support point, and symmetric and constant-velocity circles are assumed in most analyses. The condition that the torques of wrist and shoulder joints are zero is assumed as a dynamic balance condition with minimum strength. A control law is proposed to demonstrate the motion. Various properties of the dynamic balance condition are analyzed as follows. In the symmetric circles, (1) as the period of a circle decrease, the heights and the radius of the toes increase, and (2) the rotation of the body around its longitudinal axis in the double-leg circle has the effect of lifting the toes. (3) The shoulder and wrist torques can change the pose around the dynamic balance condition. In asymmetric circles, (4) the radius of the center of mass (CoM) increases as the angular velocity of the CoM around the support point decreases, and (5) the body angle with respect to the horizontal plane increases as the upward acceleration of the CoM increases. Moreover, mechanical principles of the circles are discussed as follows. (6) The CoM motion during the symmetric circles of the simple model can be related to the conical pendulum. In the simple model, (7) the pommel reaction force should be parallel to the arm segment when the wrist torque and the shoulder torque are equal or zero, and (8) to change the vertical component of the angular momentum of the body around the support point, the wrist torque around the vertical axis is needed. These results provide theoretical and qualitative insights into understanding and improving pommel horse exercise.

Cumulative Spike Train Estimation for Muscle Excitation Assessment From Surface EMG Using Spatial Spike Detection.

Estimating cumulative spike train (CST) of motor units (MUs) from surface electromyography (sEMG) is essential for the effective control of neural interfaces. However, the limited accuracy of existing estimation methods greatly hinders the further development of neural interface. This paper proposes a simple but effective approach for identifying CST based on spatial spike detection from high-density sEMG. Specifically, we use a spatial sliding window to detect spikes according to the spatial propagation characteristics of the motor unit action potential, focusing on the spikes of activated MUs in a local area rather than those of a specific MU. We validated the effectiveness of our proposed method through an experiment involving wrist flexion/extension and pronation/supination, comparing it with a recognized CST estimation method and an MU decomposition based method. The results demonstrated that the proposed method obtained higher accuracy on multi-DoF wrist torque estimation leveraging the estimated CST compared to the other three methods. On average, the correlation coefficient (R) and the normalized root mean square error (nRMSE) between the estimation results and recorded force were 0.96 0.03 and 10.1% 3.7%, respectively. Moreover, there was an extremely high interpretive extent between the CSTs of proposed method and the MU decomposition method. The outcomes reveal the superiority of the proposed method in identifying CSTs and can provide promising driven signals for neural interface.

Wrist position affects muscle fatigue during isometric contractions of wrist flexors: An exploratory study

ObjectiveTo investigate the influence of wrist position and torque level on lower arm flexor muscle fatigue. BackgroundWork-related musculoskeletal health risks at the wrist joint may depend on joint position and torque level, as proposed by ergonomic workplace assessment tools. As empirical data are scarce, muscle fatigue, as proxy of work-related musculoskeletal health risks, can be used to explore this assumption. Method18 healthy participants performed fatiguing isometric wrist flexion contractions in three wrist positions (40° flexion, 0° neutral position, and 40° extension) and torque levels (10, 20, 40% of the maximum voluntary contraction). Electromyographic signs of fatigue were analyzed in the flexor carpi radialis (FCR) and flexor digitorum superficialis (FDS) muscles. ResultsMuscle fatigue was dependent on torque level and wrist position and differed between muscles. Signs of fatigue were more evident at higher torque levels for both muscles. While fatigue signs in FCR were not clearly associated with wrist position, the FDS fatigued more during wrist flexion. An interaction effect between torque level and wrist position was not observed. ConclusionHigher torque levels induce greater signs of local muscle fatigue in wrist flexor muscles, and a 40° wrist flexion triggers fatigue, while 40° wrist extension does not. Our data do not support the assumption of increased risk in greater wrist angles in any direction by prevailing ergonomic risk assessments. Relevance to industryPeople with work-related wrist flexor effort may be at increased risk of musculoskeletal disorders when higher torques are applied and flexed wrist positions are required.

Pathophysiology of sex difference in refractoriness in lateral epicondylitis: Biomechanical study of wrist torque.

Eccentric contractions of the wrist extensors worsen lateral epicondylitis (LE), whose pathophysiology may involve sex differences in wrist torque. This study aimed to investigate sex differences in wrist torque in patients with LE. The wrist extension and flexion torques of 22 patients with LE (11 males and 11 females) were measured. Maximum muscle output over time was measured for 20 s, initial torque was defined as muscle strength, and the degree of eccentric contraction was quantified and defined as the eccentric contraction index (ECI). The affected/unaffected side ratio of the wrist extensor, extensor/flexor ratio of muscle strength, and affected/unaffected side difference of ECI between sexes were statistically analyzed. Furthermore, correlations between wrist extensor torque, ECI, and Visual Analog Scale of pain during the examination were evaluated. Females were found to display lower affected/unaffected side ratios of the wrist extensor and wrist extension/flexion ratios for the affected side, compared with males; however, no differences were found in the wrist extension/flexion ratios for the unaffected side in both sexes. Additionally, females presented with larger differences between the affected and unaffected sides in the ECI. Based on correlations between wrist torques, ECI, and pain, females tended to suppress muscle output to prevent pain from eccentric contraction of wrist extensors more than males, which would induce an imbalance in muscle strength of the wrist extensors and flexors. This imbalance may result in chronic eccentric contraction of the wrist extensors with gripping, exacerbating LE.

Muscle-Driven Joint-Torque Estimation Based on Voltage-Torque Mapping of Electrical Impedance Sensing

This paper offers an impedance sensing method taking advantage of the conductivity changes due to muscle contraction to estimate muscle-driven joint torques through a convolutional neural network (CNN) where the input images are derived from a finite set of boundary voltage measurements. Guided by a physical model combining the forearm biomechanics and the muscle electric field along with the CNN criteria considering the receptive fields, the effects of two image formats (for quasi-static and dynamic states) on the CNN performance are experimentally studied on eight human subjects’ forearms using a prototype impedance sensing system. By comparing the CNN-estimated torques with that measured on a haptic device, the findings verify that the impedance-based method can estimate the joint torques driven by both the deep and superficial muscles within 9% errors of the three degrees-of-freedom wrist torque and 10% error of the gripping torque, and that it is feasible to share data among a similar group to reduce data collection and time when training a CNN for uses on a new subject.

Corticospinal interface to restore voluntary control of joint torque in a paralyzed forearm following spinal cord injury in non-human primates.

The corticospinal tract plays a major role in the control of voluntary limb movements, and its damage impedes voluntary limb control. We investigated the feasibility of closed-loop brain-controlled subdural spinal stimulation through a corticospinal interface for the modulation of wrist torque in the paralyzed forearm of monkeys with spinal cord injury at C4/C5. Subdural spinal stimulation of the preserved cervical enlargement activated multiple muscles on the paralyzed forearm and wrist torque in the range from flexion to ulnar-flexion. The magnitude of the evoked torque could be modulated by changing current intensity. We then employed the corticospinal interface designed to detect the firing rate of an arbitrarily selected "linked neuron" in the forearm territory of the primary motor cortex (M1) and convert it in real time to activity-contingent electrical stimulation of a spinal site caudal to the lesion. Linked neurons showed task-related activity that modulated the magnitude of the evoked torque and the activation of multiple muscles depending on the required torque. Unlinked neurons, which were independent of spinal stimulation and located in the vicinity of the linked neurons, exhibited task-related or -unrelated activity. Thus, monkeys were able to modulate the wrist torque of the paralyzed forearm by modulating the firing rate of M1 neurons including unlinked and linked neurons via the corticospinal interface. These results suggest that the corticospinal interface can replace the function of the corticospinal tract after spinal cord injury.

Sex differences in wrist torque and endurance-Biomechanical factors associated with developing lateral epicondylitis of the humerus.

Since eccentric contractions contribute to the development of tendinopathy, sex differences in wrist torque and endurance may be involved in the pathophysiology of lateral epicondylitis and its refractoriness. Therefore, the present study investigated sex differences in wrist torque and endurance. The wrist extension and flexion torques of the 100 wrists of 25 males and 25 females were measured. The following parameters were assessed: muscle strength at the starting- and end point for the measurement, Δ muscle strength, that is, the amount of a loss over time, and the muscle endurance ratio, that is, the decrease rate over time. Each parameter in males and females was statistically analyzed. In wrist extension, muscle strength at the starting point was 6.1 Nm for males and 3.3 Nm for females (p < 0.001); Δ Muscle strength was -0.052 Nm/sfor males and -0.038 Nm/sfor females (p = 0.036); The muscle endurance ratio was 99.1%/sfor males and 98.8%/sfor females (p = 0.015). In wrist flexion, muscle strength at the starting point and absolute value of Δ muscle strength were significantly larger in males than in females; No significant difference was observed in the muscle endurance ratio in wrist flexion between males and females. These results revealed sex differences in wrist torque and endurance. The muscle endurance ratio of the wrist extensors was lower in females than in males, which suggests that females need to exert more effort to maintain the wrist extension position under resistance. This may predispose the wrist extensor muscles in females to eccentric contractions.

Mapping Individual Motor Unit Activity to Continuous Three-DoF Wrist Torques: Perspectives for Myoelectric Control.

The surface electromyography (EMG) decomposition techniques provide access to motor neuron activities and have been applied to myoelectric control schemes. However, the current decomposition-based myoelectric control mainly focuses on discrete gestures or single-DoF continuous movements. In this study, we aimed to map the motor unit discharges, which were identified from high-density surface EMG, to the three degrees of freedom (DoFs) wrist movements. The 3-DoF wrist torques and high-density surface EMG signals were recorded concurrently from eight non-disabled subjects. The experimental protocol included single-DoF movements and their various combinations. We decoded the motor unit discharges from the EMG signals using a segment-wise decomposition algorithm. Then the neural features were extracted from motor unit discharges and projected to wrist torques with a multiple linear regression model. We compared the performance of two neural features (twitch model and spike counting) and two training schemes (single-DoF and multi-DoF training). On average, 145 ± 33 motor units were identified from each subject, with a pulse-to-noise ratio of 30.8 ± 4.2 dB. Both neural features exhibited high estimation accuracy of 3-DoF wrist torques, with an average [Formula: see text] of 0.76 ± 0.12 and normalized root mean square error of 11.4 ± 3.1%. These results demonstrated the efficiency of the proposed method in continuous estimation of 3-DoF wrist torques, which has the potential to advance dexterous myoelectric control based on neural information.

Tuning of motor outputs produced by spinal stimulation during voluntary control of torque directions in monkeys.

Spinal stimulation is a promising method to restore motor function after impairment of descending pathways. While paresis, a weakness of voluntary movements driven by surviving descending pathways, can benefit from spinal stimulation, the effects of descending commands on motor outputs produced by spinal stimulation are unclear. Here, we show that descending commands amplify and shape the stimulus-induced muscle responses and torque outputs. During the wrist torque tracking task, spinal stimulation, at a current intensity in the range of balanced excitation and inhibition, over the cervical enlargement facilitated and/or suppressed activities of forelimb muscles. Magnitudes of these effects were dependent on directions of voluntarily produced torque and positively correlated with levels of voluntary muscle activity. Furthermore, the directions of evoked wrist torque corresponded to the directions of voluntarily produced torque. These results suggest that spinal stimulation is beneficial in cases of partial lesion of descending pathways by compensating for reduced descending commands through activation of excitatory and inhibitory synaptic connections to motoneurons.

Human Perception of Wrist Flexion and Extension Torque During Upper and Lower Extremity Movement.

Real-world application of haptic feedback from kinesthetic devices is implemented while the user is in motion, but human wrist torque magnitude discrimination has previously only been characterized while users are stationary. In this study, we measured wrist torque discrimination in conditions relevant to activities of daily living, using a previously developed backdrivable wrist exoskeleton capable of applying wrist flexion and extension torque. We implemented a torque comparison test using a two-alternative forced-choice paradigm while participants were both seated and walking on a treadmill, with both a stationary and a moving wrist. Like most kinesthetic haptic devices, the wrist exoskeleton output torque is commanded in an open-loop manner. Thus, the study design was informed by Monte Carlo simulations to verify that the errors in the wrist exoskeleton output torque would not significantly affect the results. Results from ten participants show that although both walking and moving wrist conditions result in higher Weber Fractions (worse perception), participants were able to detect relatively small changes in torque of 12-19% on average in all grouped conditions. The results provide insight regarding the torque magnitudes necessary to make wrist-worn kinesthetic haptic devices noticeable and meaningful to the user in various conditions relevant to activities of daily living.

Manipulator Equipped With Differential Wrist Mechanism to Combine the Torque of Two Motors to Increase Fingertip Force and Wrist Torque

A lightweight and high-output manipulator is introduced in this letter. The manipulator comprises two parts: a robot hand part and a wrist part. The total weight of the robot hand part is approximately 450 g, and its size is almost the same as that of a human hand. Furthermore, a design concept of a differential mechanism is presented in this letter. In contrast to traditional mechanisms, in which the movement of a single motor corresponds to a single module, the proposed differential mechanism can superimpose the output forces of multiple motors and act on the movement of single or multiple modules; consequently, the output force is doubled, the low-power requirement of the motor, which drives the robot hand as the end effector to rotate around the wrist, is met, and the driving force amplification mechanism amplifies the gripping force of the fingers. The proposed differential mechanism is incorporated in the wrist part. The robot hand part is responsible for the fast grasping of objects. The wrist part is responsible for increasing the output force of the fingers to ensure a firm grasp. In addition, it enables the robot hand to rotate around the wrist. It takes 0.32 s for the fingers to transition from moving to touching the object. It takes approximately 0.9 s to grasp the object firmly, and the output force of the fingertips can reach 25.5 N. The robot hand can rotate 135 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> around the wrist, and the rotation speed is 118 deg/s.

Evaluation of a Portable fMRI Compatible Robotic Wrist Interface.

This paper presents evaluation of a portable fMRI compatible haptic interface to study the brain correlates of sensorimotor control during wrist motion. The interface is actuated by a shielded DC motor located more than 2 m away from the 3T MR scanner's bore. The achievable wrist torque of the interface is up to 2 Nm, and the interface provides sufficient bandwidth for human motor control experiments. Ergonomic and fMRI compatibility testing with a 3T MR scanner showed that the interface is MR safe, compatible with a strong static magnetic field and radio frequency emission, and its operation does not affect the quality of the acquired images. Clinical Relevance- We present and evaluate an fMRI compatible robotic interface to study human wrist joint motor function.

A Co-driven Functional Electrical Stimulation Control Strategy by Dynamic Surface Electromyography and Joint Angle.

Functional electrical stimulation (FES) is widely used in neurorehabilitation to improve patients’ motion ability. It has been verified to promote neural remodeling and relearning, during which FES has to produce an accurate movement to obtain a good efficacy. Therefore, many studies have focused on the relationship between FES parameters and the generated movements. However, most of the relationships have been established in static contractions, which leads to an unsatisfactory result when applied to dynamic conditions. Therefore, this study proposed a FES control strategy based on the surface electromyography (sEMG) and kinematic information during dynamic contractions. The pulse width (PW) of FES was determined by a direct transfer function (DTF) with sEMG features and joint angles as the input. The DTF was established by combing the polynomial transfer functions of sEMG and joint torque and the polynomial transfer functions of joint torque and FES. Moreover, the PW of two FES channels was set based on the muscle synergy ratio obtained through sEMG. A total of six healthy right-handed subjects were recruited in this experiment to verify the validity of the strategy. The PW of FES applied to the left arm was evaluated based on the sEMG of the right extensor carpi radialis (ECR) and the right wrist angle. The coefficient of determination (R2) and the normalized root mean square error (NRMSE) of FES-included and voluntary wrist angles and torques were used to verify the performance of the strategy. The result showed that this study achieved a high accuracy (R2 = 0.965 and NRMSE = 0.047) of joint angle and a good accuracy (R2 = 0.701 and NRMSE = 0.241) of joint torque reproduction during dynamic movements. Moreover, the DTF in real-time FES system also had a nice performance of joint angle fitting (R2 = 0.940 and NRMSE = 0.071) and joint torque fitting (R2 = 0.607 and NRMSE = 0.303). It is concluded that the proposed strategy is able to generate proper FES parameters based on sEMG and kinematic information for dynamic movement reproduction and can be used in a real-time FES system combined with bilateral movements for better rehabilitation.

Biomechanical Modeling of Brachialis-to-Wrist Extensor Muscle Transfer Function for Daily Activities in Tetraplegia.

A model of the transferred BRA-ECRB muscle-tendon unit was developed to calculate isometric elbow and wrist joint torque as a function of elbow and wrist angles resulting from different BRA reattachment locations from 50 to 80 mm proximal to the wrist joint crease. Using this model, mathematical optimization predicted the optimal location for BRA reattachment in order to perform each of a number of important upper extremity tasks as well as to calculate a global optimum for performing all of the tasks. Analysis of active joint torque showed that the entire elbow torque-angle curve surface shifted "diagonally" toward elbow flexion and wrist extension as the attachment location approached the wrist joint; peak wrist torque was produced at extended wrist angles. Our model predicted that the optimal attachment location for each different task ranged from 54.3 to 74.6 mm proximal to the wrist joint, which is feasible given the anatomy of the muscle-tendon unit. The attachment location to optimize performing all tasks was calculated as 63.5 mm proximal to the wrist joint. This study clearly demonstrates that the BRA, which is underused as a donor in tetraplegia surgery, is an excellent donor muscle to provide wrist extension. Biomechanical simulation further highlighted the need to consider not only donor-muscle appropriateness but the patient's desired function when planning surgical tendon transfers. Quantitative evaluation of the way that surgery affects daily tasks rather than simply matching muscle properties may be a more appropriate approach for surgeons to use when choosing and tensioning donor muscles.

Kinetic Analysis of the Fingers Under Different Ball Velocities During Overarm Throwing.

The purpose of this study is to examine changes in the kinetic parameters of the fingers caused by differences in ball velocity during overarm throwing. Six baseball players participated in the study, and the kinetics of the wrist and metacarpophalangeal (MP) joint were calculated using an inverse dynamics method. The results of Tukey's multiple comparison tests showed that the torque and work of the wrist increased with increasing ball velocity (p < .05), indicating that wrist torque and work contributed to the adjustment of ball velocity. Peak MP joint torque also increased with ball velocity (p < .05), although the work of the MP joint remained relatively constant. We conclude that MP joint torque and work contribute to the achievement of stable ball release rather than adjusting ball velocity.

Evaluating Viscoelastic Properties of the Wrist Joint During External Perturbations: Influence of Velocity, Grip, and Handedness.

In this study, we designed a robot-based method to compute a mechanical impedance model that could extract the viscoelastic properties of the wrist joint. Thirteen subjects participated in the experiment, testing both dominant and nondominant hands. Specifically, the robotic device delivered position-controlled disturbances in the flexion-extension degree of freedom of the wrist. The external perturbations were characterized by small amplitudes and fast velocities, causing rotation at the wrist joint. The viscoelastic characteristics of the mechanical impedance of the joint were evaluated from the wrist kinematics and corresponding torques. Since the protocol used position inputs to determine changes in mean wrist torque, a detailed analysis of wrist joint dynamics could be made. The scientific question was whether and how these mechanical features changed with various grip demands and perturbation velocities. Nine experimental conditions were tested for each hand, given by the combination of three velocity perturbations (fast, medium, and slow) and three hand grip conditions [self-selected grip, medium and high grip force, as percentage of the maximum voluntary contraction (MVC)]. Throughout the experiments, electromyographic signals of the extensor carpi radialis (ECR) and the flexor carpi radialis (FCR) were recorded. The novelty of this work included a custom-made soft grip sensor, wrapped around the robotic handle, to accurately quantify the grip force exerted by the subjects during experimentation. Damping parameters were in the range of measurements from prior studies and consistent among the different experimental conditions. Stiffness was independent of both direction and velocity of perturbations and increased with increasing grip demand. Both damping and stiffness were not different between the dominant and nondominant hands. These results are crucial to improving our knowledge of the mechanical characteristics of the wrist, and how grip demands influence these properties. This study is the foundation for future work on how mechanical characteristics of the wrist are affected in pathological conditions.

Anthropometrics and electromyography as predictors for maximal voluntary isometric wrist torque: Considerations for ergonomists

The purpose of this study was to evaluate anthropometry and forearm muscle activity as predictors of maximal isometric wrist torque. Thirteen anthropometric measures, forearm electromyography from flexor carpi radialis (FCR) and extensor carpi radialis (ECR), and maximal isometric wrist flexion/extension torque were obtained from 25 male participants. Pearson correlation coefficients assessed relationships between peak isometric torque and: (1) anthropometrics, (2) FCR and ECR activation, (3) FCR/ECR antagonist/agonist coactivation ratios. Based on significant correlations, linear regression equations were developed (SPSS v.25; p < 0.05). Hand thickness, forearm circumference and ECR activation or hand thickness, elbow circumference, FCR activation and body weight were most highly correlated with extension or flexion torque, respectively. Hand thickness, forearm circumference, and ECR activation (R2 = 54.5%; p = 0.001) and hand thickness, elbow circumference, FCR activation (R2 = 68.3%; p < 0.001) explained similar variance in torque regressions as did the addition of body weight to extension (R2 = 58.0%; p = 0.001) and flexion (R2 = 69.9%; p < 0.001) torque regression equations, respectively. Circumference measurements, a pseudo for muscle size, and activation amplitude influenced wrist force output more than limb length or coactivation.

Mismatch between jar opening demands and wrist torque strength of consumers in Iran

This study evaluated the potential mismatch between vacuum-sealed jar opening demands and wrist torque strength of 758 (384 males and 374 females) participants aged 5–74 years in Iran. Wrist ulnar/radial (U/R) torque strength of participants and required torque for opening the existing jars (with 2 different sizes – 65 mm and 85 mm diameter lids) were measured using a digital angle torque adaptor and then compared together to identify any potential mismatch between them. The mismatch percentages were defined as the number of participants whose maximal wrist U/R torque strength were lower than the minimum required torque strength for opening the vacuum-sealed jars. Minimum required torque strength for opening the existing 65 mm and 85 mm vacuum-sealed jars were 4.1 Nm and 6.6 Nm, respectively (range = 4.1 Nm to 10.2 Nm). A considerable mismatch (range = 25%–100%) was found between the required torque strength for opening the existing jars and the wrist U/R torque strength of the study population, particularly for females and those aged 5–9 years. A torque limit of 1.8 Nm was proposed for opening jars for the entire population.

Initial stages of hand osteoarthritis do not affect the extrinsic muscles of the hand: a cross-sectional study

The objective of this study was to verify whether women in the initial stages of hand osteoarthritis (HOA) already have impaired grip strength and flexor and extensor torque of the wrist compared to healthy women. It also aimed to correlate these variables with pain, stiffness, and function of the hand. Twenty-six women were divided into a control group [CG, n = 13; 56 (51–61) years old] and a hand osteoarthritis group [HOAG, n = 13; 58 (53–63) years old]. Grades II and III were included in the HOA group according to the criteria of Kellgren and Lawrence. All volunteers answered an initial assessment form, the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire and the Australian/Canadian Hand Osteoarthritis Index (AUSCAN). The grip strength and isometric wrist flexor and extensor torque were evaluated by a hydraulic dynamometer. Comparisons between groups used Student’s t test for independent samples and the Mann–Whitney test. Spearman's correlation was used to correlate grip strength and flexor and extensor wrist torque to the degree of disease and DASH and AUSCAN scores. There were no differences between the groups in grip strength or flexor and extensor torque values. In terms of the DASH and the AUSCAN, the HOA group had higher scores, indicating worse hand function. A strong negative correlation was found between grip strength and the degree of HOA (r = − 0.70, p = 0.008), and a moderate positive correlation was found between flexor torque and the degree of HOA (r = 0.53, p = 0.05). The pain (r = − 0.61, p = 0.02) and function (r = − 0.66, p = 0.01) sections of the AUSCAN correlated negatively with grip strength. Pain can be an important feature in the HOA rehabilitation process, as it can influence handgrip strength and function. It is important that rehabilitation is implemented as soon as possible to guarantee the maintenance of strength and function since with the severity of the disease, patients tend to have deficits in grip strength and function.

Kinetic analysis of the wrist and fingers during fastball and curveball pitches

This study had two objectives: (a) revealing kinetic parameter differences at the fingers during a fastball and curveball, and (b) examining timing control between the wrist and finger torques. The participants were eight baseball pitchers. The kinetics of the wrist and fingers were calculated using an inverse dynamics method. The peak torque and work of finger adduction during the curveball was significantly larger than that during the fastball. During the fastball pitch, the maximal correlation coefficient between the wrist flexion torque and finger flexion torque was very high (r = 0.94 ± 0.05). The reasons for this result are twofold: (a) the extrinsic finger muscles cross the wrist (biarticular muscle) and (b) the wrist flexion torque during the fastball pitch acts in the direction of acceleration of the ball. During the curveball pitch, we found two typical types of wrist and finger torque control. Furthermore, the two pitchers exerted large wrist extension and radial torque, and finger adduction torque. Although the other six pitchers hardly exerted these torques, they exerted wrist flexion torque predominantly. It was considered that the six pitchers selected wrist flexion torque as the control for the fastball and curveball pitch to confuse the batter.