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Project
Functional anatomy and biomechanics of brachiating gibbons (Hylobatidae): an example of locomotion in complex environments.
Recent literature on the biomechanics of arboreal locomotion revealed that gibbons are able to brachiate with very low mechanical costs. They do this by making pendular movements, continually exchanging potential and kinetic energy to optimally conserve energy. In addition, they must minimise their collisional energy losses by ensuring that the passage between two movements happens smoothly without abrupt changes in the path of the body centre of mass. Although the animals appear to succeed in doing this in uniform, predictable experimental circumstances, this cannot provide satisfactory detail of the degree of co-ordination and control in more naturalistic complex surroundings with compliant and heterogeneously spaced branches
In this PhD project we used a combination of morphological, kinematical and dynamical analyses to question whether gibbons adjust their movement patterns adequately to the mechanical complexity of support structures.
The first two chapters discuss the functional anatomy of hylobatids in relation to brachiation as their primary locomotion mode. The shoulder flexors, extensors, rotator muscles, elbow flexors and wrist flexors seem shaped to contribute the most to brachiation. Particularly the elbow flexors of gibbons are more powerful compared to those of non-specialised brachiators. In addition, both elbow and wrist flexors stand out in terms of moment of force-generating capacity, compared to non-brachiating species. Siamang forelimb muscles perform at their maximum during brachiation. However, the elbow flexors may be adapted to more demanding movements, given that maximal output is reached at the stronger flexed elbow positions which are reached during brachiation in a more spatially complex setup.
In chapter 3, a kinematical study of continuous contact brachiation in a simplified environment revealed four locomotory transitions that are mainly associated with speed. The results showed that regardless of the transition type, energy recovery is always relatively high and collision fraction relatively low.
Chapter 4 discusses the effect of spatial heterogeneity of available support structures and brachiation speed on brachiation mechanics. Energy recovery was observed to be primarily determined by brachiation speed. Furthermore, the results indicate that collisional losses seem to be avoided during all the experimental setups used in this study. The expected effect of increasing spatial complexity, however, was not found: the energy recovery is kept high in all presented situations, except when brachiating at higher speed.
Finally, chapter 5 examines the effect of a compliant support structure on brachiation. The two individuals that were studied each had a different strategy to cope with the compliant handhold. One animal consistently used continuous contact brachiation and avoided additional lowering of the body centre of mass due to spring elongation by lifting the free, swing arm and lifting the legs. The other animal avoided the compliant handhold regularly by ricocheting over the setup without grabbing the compliant handhold. However, when take-off from the previous rigid handhold was not with the right velocity or timing to ensure successful grabbing of the next rigid handhold, the compliant handhold was shortly used with a low force (and a large variance between sequences). For both strategies, the use of the compliant handhold induced a lower energy recovery an increased collision fraction. However, for both animals, the energy recovery increased and the collision fraction decreased when the body centre of mass followed the spring elongation less.
Although the complexity of the environment seems to determine brachiation mechanics, the effective use of the powerful forelimb muscles can easily adjust the movements during brachiation, assuring contact with the next available support and in addition, keeping energy exchange relatively high and collisional losses relatively low, even in a complex environment.
In this PhD project we used a combination of morphological, kinematical and dynamical analyses to question whether gibbons adjust their movement patterns adequately to the mechanical complexity of support structures.
The first two chapters discuss the functional anatomy of hylobatids in relation to brachiation as their primary locomotion mode. The shoulder flexors, extensors, rotator muscles, elbow flexors and wrist flexors seem shaped to contribute the most to brachiation. Particularly the elbow flexors of gibbons are more powerful compared to those of non-specialised brachiators. In addition, both elbow and wrist flexors stand out in terms of moment of force-generating capacity, compared to non-brachiating species. Siamang forelimb muscles perform at their maximum during brachiation. However, the elbow flexors may be adapted to more demanding movements, given that maximal output is reached at the stronger flexed elbow positions which are reached during brachiation in a more spatially complex setup.
In chapter 3, a kinematical study of continuous contact brachiation in a simplified environment revealed four locomotory transitions that are mainly associated with speed. The results showed that regardless of the transition type, energy recovery is always relatively high and collision fraction relatively low.
Chapter 4 discusses the effect of spatial heterogeneity of available support structures and brachiation speed on brachiation mechanics. Energy recovery was observed to be primarily determined by brachiation speed. Furthermore, the results indicate that collisional losses seem to be avoided during all the experimental setups used in this study. The expected effect of increasing spatial complexity, however, was not found: the energy recovery is kept high in all presented situations, except when brachiating at higher speed.
Finally, chapter 5 examines the effect of a compliant support structure on brachiation. The two individuals that were studied each had a different strategy to cope with the compliant handhold. One animal consistently used continuous contact brachiation and avoided additional lowering of the body centre of mass due to spring elongation by lifting the free, swing arm and lifting the legs. The other animal avoided the compliant handhold regularly by ricocheting over the setup without grabbing the compliant handhold. However, when take-off from the previous rigid handhold was not with the right velocity or timing to ensure successful grabbing of the next rigid handhold, the compliant handhold was shortly used with a low force (and a large variance between sequences). For both strategies, the use of the compliant handhold induced a lower energy recovery an increased collision fraction. However, for both animals, the energy recovery increased and the collision fraction decreased when the body centre of mass followed the spring elongation less.
Although the complexity of the environment seems to determine brachiation mechanics, the effective use of the powerful forelimb muscles can easily adjust the movements during brachiation, assuring contact with the next available support and in addition, keeping energy exchange relatively high and collisional losses relatively low, even in a complex environment.
Date:1 Jul 2008 → 12 Sep 2012
Project type:PhD project