Available response time for female pitchers in youth through collegiate fastpitch softball.

The purpose of this study was to quantify the relationship between age and available response time in fastpitch softball for pitchers, which is necessary to evaluate the efficacy of interventions designed to decrease player response times and determine if player protective equipment are necessary. High speed video was used to measure ball impact location relative to home plate, swing speed, and ball exit velocity of 588 swings taken by 87 female fastpitch softball players 9 to 24 years old. Available response time considered age-appropriate ball aerodynamics, field dimensions, ball impact location, and pitcher advancement during pitch delivery.

Effect of Subject-Specific Vertebral Position and Head and Neck Size on Calculation of Spine Musculoskeletal Moments.

Spine musculoskeletal models used to estimate loads and displacements require many simplifying assumptions. We examined how assumptions about subject size and vertebral positions can affect the model outcomes. Head and neck models were developed to represent 30 subjects (15 males and 15 females) in neutral posture and in forward head postures adopted while using tablet computers.

Gravitational demand on the neck musculature during tablet computer use.

Tablet computer use requires substantial head and neck flexion, which is a risk factor for neck pain. The goal of this study was to evaluate the biomechanics of the head-neck system during seated tablet computer use under a variety of conditions. A physiologically relevant variable, gravitational demand (the ratio of gravitational moment due to the weight of the head to maximal muscle moment capacity), was estimated using a musculoskeletal model incorporating subject-specific size and intervertebral postures from radiographs.

Inter-individual variation in vertebral kinematics affects predictions of neck musculoskeletal models.

Experimental studies have found significant variation in cervical intervertebral kinematics (IVK) among healthy subjects, but the effect of this variation on biomechanical properties, such as neck strength, has not been explored. The goal of this study was to quantify variation in model predictions of extension strength, flexion strength and gravitational demand (the ratio of gravitational load from the weight of the head to neck muscle extension strength), due to inter-subject variation in IVK. IVK were measured from sagittal radiographs of 24 subjects (14F, 10M) in five postures: maximal extension, mid-extension, neutral, mid-flexion, and maximal flexion.