The first conclusion that can be drawn from this study is that the LifeModeler™ default model was not adequate to solve the forward dynamics simulations forany of the anthropometric cases. In order to solve this the following adjustments were made to the default model: 1) an increase in the pCSA of the three default elbow flexor muscles, 2) manipulate the muscle origins and insertions and 3) decrease the joint stiffness in the forwards dynamics simulations.
Muscle tension depends on several factors including neural activation, pCSA, muscle architecture and muscle length (Durall, 2004). The pCSA of the BBL, BBS and B muscles had to be increased for all three anthropometric cases by 50% (Table IX). Due to differences in measurement methodology anatomical cross-sectional areas (aCSA) are smaller than pCSAs (Akagi et al., 2009).
Despite this difference, the adjustments resulted in significantly larger pCSAs when compared to elbow flexor muscle anatomical cross-sectional area (aCSA) measurements by magnetic resonance imaging (MRI) in young males and females of 182 mm2 and 103 mm2 respectively (Akagi et al., 2009). These adjustments however were necessary in order to solve the forward dynamics simulations. It is interesting to note that the pCSA area for the 50th percentile male was larger than that of the 95th percentile male for both muscle groups. The apparent reasoning for this discrepancy according to the manufacturers of the software has to do with the proportionality of the volume differences between the two cases. The 95th percentile male is 146mm taller but the increase in body mass was only 6kg therefore there was approximately a 9% increase in height with only a 9% increase in volume. To keep proportionality, volume should increase three times more than stature. Thus, caution should be employed when using the default model to not assume that a matching anthropometry will result in reliable muscle strength capabilities; this is further complicated by the significant variance in muscular strength between subjects of similar anthropometry due to differences in conditioning levels.
A 3D musculoskeletal full body model was created using LifeModeler™ software and incorporated into a multibody dynamics model of the abdominal crunch machine modelled in MSC ADAMS (Figure 1). The LifeModeler™ software runs as a plug-in on the MSC ADAMS software. LifeModelerTM software has previously been used in studies in the fields of sport, exercise and medicine (Schillings et al., 1996; Rietdyk and Patla., 1999; Hofmann et al., 2006; Agnesina et al., 2006; De Jongh, 2007; Olesen et al., 2009). It was decided to evaluate a default model as generated through the software. This model consists of 19 segments including a base set of joints for each body region. Specifically, the spine does not consist of individual vertebrae but rather of various segments that represent different regions of the vertebral column with joints between these segments. The default model has a full body set of 118 muscle elements attached to the bones at anatomical landmarks, which includes most of the major muscle groups in the body. Closed loop simple muscles were modelled. Closed loop muscles contain proportional-integral-differential (PID) controllers. The PID controller algorithm uses a target length-time curve to generate the muscle activation and the muscles follow this curve. Because of this approach, an inverse dynamics simulation using passive recording muscles is required prior to simulation with closed loop muscles. Simple muscles fire with no constraints except for the physiological cross-sectional area (pCSA), which designates the maximum force a muscle can exert. The graphs of simple muscle activation curves will generally peak at a flat force ceiling value (Biomechanics research group, 2006).
CHAPTER 1: GENERAL INTRODUCTION
1.1 THREE DIMENSIONAL MUSCULOSKELETAL MODELLING
1.2 PROBLEM FORMULATION
1.3 GOALS AND OBJECTIVES
1.5 RESEARCH APPROACH
1.6 STRUCTURE OF THE THESIS
CHAPTER 2: OVERVIEW (RESISTANCE TRAINING)
2.1 EXERCISE AND EXERCISE EQUIPMENT
2.2 RESISTANCE TRAINING
CHAPTER 3: THREE DIMENSIONAL MUSCULOSKELETAL MODELLING OF THE SEATED BICEPS CURL RESISTANCE TRAINING EXERCISE FOCUSING ON THE BIOMECHANICAL AND ANTHROPOMENTRIC CONSIDERATIONS OF THE END-USER
CHAPTER 4: THREE DIMENSIONAL MUSCULOSKELETAL MODELLING OF THE ABDOMINAL CRUNCH RESISTANCE TRAINING EXERCISE FOCUSING ON THE BIOMECHANICAL AND ANTHROPOMETRIC CONSIDERATIONS OF THE END-USER
CHAPTER 5: THREE DIMENSIONAL MUSCULOSKELETAL MODELLING OF THE SEATED ROW RESISTANCE TRAINING EXERCISE FOCUSING ON THE BIOMECHANICAL AND ANTHROPOMETRIC CONSIDERATIONS OF THE END-USER
CHAPTER 6: THREE DIMENSIONAL MUSCULOSKELETAL MODELLING OF THE CHEST PRESS RESISTANCE TRAINING EXERCISE FOCUSING ON THE BIOMECHANICAL AND ANTHROPOMETRIC CONSIDERATIONS OF THE END-USER
CHAPTER 7: SUMMARY, GENERAL CONCLUSIONS AND RECOMMENDATIONS
7.2 GENERAL CONCLUSION