Hand-Wrist Torque MVC Estimation in a Sample of Mexican Students.
This study presents the estimation of maximum volunteer contraction (MVC) of hand-wrist torque during forearm pronation and supination in three different forearm positions: maximum pronation, neutral position and maximum supination. Jobs involving manual application of hand wrist torque represent a high risk of injuries at wrist level. Hand tools need to be adjusted to users, considering user’s capability in order to obtain a better performance during the task and prevent injuries. Our aim was to create tolerances parameters that can be useful in the design of hand tools, tasks and products that involve the application of this effort. Physical measures of MVC were registered during forearm maximum pronation (Pmax), neutral position (N), and maximum supination (Smax) in a sample of healthy Mexican students from a local university; height and weight, and anthropometric measurements of the dominant upper extremity were also obtained; electrical muscle activity from the biceps brachii was recorded using surface electromyography; an inclinometer was used to measure forearm range of motion. Results showed that men obtained higher values than women during the application of MVC. The highest MVC was registered during supination with forearm starting at maximum pronation (Pmax-S) in which men could exert 9.02 ± 2.25 Nm and women 4.30 ± 1.65 Nm. Significant differences between MVC applied during the different forearm positions. Additionally, biceps brachii registered the highest electrical activity when applying supination MVC starting at maximum supination (Smax-S). It is suggested that for manual work requiring application of supination MVC hand-wrist torque, it should be carried out starting with forearm at maximum supination position, and should not exceed 2.70 Nm for men, and 1.29 Nm for women, in order to avoid the presence of musculoskeletal fatigue and consequently pain or discomfort at upper limb level.