Three dimensional musculoskeletal modelling of the abdominal crunch resistance training exercise.

The aim of this study was to evaluate the benefits and limitations of using three dimensional (3D) musculoskeletal modelling (LifeModeler) in assessing the safety and efficacy of exercising on an abdominal crunch resistance training machine. Three anthropometric cases were studied, representing a 5th percentile female, and 50th percentile and 95th percentile male. Results indicated that the LifeModeler default model was capable of solving the forward dynamics simulations without adjustments. The modelling was able to indicate high risk for back injury when performing the abdominal crunch exercise as a result of the unacceptable intervertebral joint loading that occurs during the exercise. Individuals with small anthropometric dimensions such as some females and children cannot be accommodated suitably on the abdominal crunch machine which negatively impacts exercise posture and technique. Hip flexor muscle contribution in the execution of the exercise for the 5th percentile female was substantial thus reducing the efficacy of the exercise in isolating the abdominal muscles.