larger primates are too heavy to exploit food resources on the ends of branches, gibbons can remain suspended for a significant period and use their long arms to reach food in terminal branches more easily. Another theory postulates that brachiation is a quieter and less obvious mode of locomotion than quadrupedal jumping and climbing thereby more successfully avoiding predators. Types of brachiation Continuous contact This form of brachiation occurs when the primate is moving at slower speeds and is characterized by the animal maintaining constant contact with a handhold, such as a tree branch. This gait type utilizes the passive exchange between two types of energy, gravitational potential and translational kinetic, to propel the animal forward at a low mechanical cost. This mode of brachiation has been compared to the movement patterns of bipedal walking in humans. Ricochetal This type of brachiation is used by primates to move at faster speeds and is characterized by a flight phase between each contact with a handhold. Ricochetal brachiation uses an exchange of translational and rotational kinetic energy to move forward, and is compared to a "whip-like" motion. Due to its aerial phase, ricochetal brachiation is similar to bipedal running in humans. Models of brachiation Pendulum movement Continuous contact brachiation has often been compared to the movement of a simple pendulum. This is due to the out-of-phase fluctuation of energy that occurs while the moving primate is swinging between each tree appendage as the energy transfers from potential to kinetic, and vice versa. The use of gravitational acceleration to effect movement can be found in both the brachiating primate and the moving ball in a pendulum model. A brachiator can make use of this momentum in several different ways: during the downswing the primate can maximize its change in kinetic energy, during the upswing it can minimize loss of kinetic energy or it can avoid moving laterally during its upward swing. Brachiating primates have adapted these three strategies for maximizing forward movement by adjusting its posture during each swing. The amount of energy transferred from potential to kinetic during pendulum-like movement is known as energy recovery. Maintaining a higher energy recovery during brachiation costs less energy and allows the animal to move to its destination quickly, however, this type of movement is also harder to control. Therefore, since the risk of missing a handhold can result in injury or death, the benefit of