These features allow the flexed toe tips to be locked into the plantar aspect of the metatarsophalangeal joints and then the locked digits to be rolled into the sole (the double-locking mechanism) when orangutans grip the small-diameter supports (Schultz, 1963 Gomberg, 1981). As exhibited by analogous bones of the hand, the foot of orangutans possesses relatively elongated and curved metatarsal and phalangeal bones and a flexion set of the toe joints, resulting in the hook-like appearance of the foot (Schultz, 1963 Tuttle, 1970, 1972 Gomberg, 1981 Rose, 1988 Griffin & Richmond, 2010 Marchi, 2010). The morphology of the bones and joints enable the orangutan foot to function as a suspensory supporting organ, whereas chimpanzees have a plantigrade foot. These differences in foot muscle dimensions of the two species suggest that the orangutan is more specialized for hook-like digital gripping without involvement of the rudimentary hallux, while the chimpanzee is adapted to hallux-assisted power gripping in arboreal locomotion. The mass and PCSA ratios of the hallucal muscles were larger in chimpanzees. Moreover, the medial components of the intrinsic muscles exhibited relatively larger mass and PCSA ratios in orangutans. The results indicate that the pedal interosseous and the intrinsic pedal digital extensor muscles in the orangutans probably have higher capacity for force production due to their relatively larger PCSAs than in chimpanzees. Muscle mass and PCSA were divided by the total mass and total PCSA of the entire foot muscles for normalization. On the other hand, chimps and other nonhuman primitives have only a working version.The hindlimbs of two orangutans and four chimpanzees were dissected, and muscle parameters (mass, fascicle length, and physiological cross-sectional area: PCSA) were determined to explore possible interspecies variation in muscle dimensions. Humans with two working versions of the gene are basically overrepresented among the elite sprinters while the nonworking versions are overrepresented among the endurance runners. Most people have lost another muscleвЂ“related gene called ACTN3. In people, MYH16 has actually been deactivated.

In recent studies, genetics have identified loci to be the cause of some of the anatomicalВ differences.ДЇor example, one gene called the MYH16 contributed to the growth and development of very huge jaw muscles in apes. The chimpanzeeвЂ™s skeletal structure has longer fibers compared to that of the human and can therefore generate double the total work output. Human GeneticsДЄ chimp on four legs can easily outrun a world-class human sprinter. They also use their upper bodies for walking. That is because they live in an environment that involves climbing lots of trees and swinging from tree to tree. In fact, their grip is especially strong. Upper Body StrengthД¬himpanzees have very strong upper bodies. On the other hand, chimps do not need two legs to run so this muscle is weak. The reason we have strong gluteal muscles is because these muscles are used to pull the leg back at the hip while running. A human being has a very strong bottom muscle which does not exist in a chimpanzee. In some ways, humans are actually stronger that chimps. Over the years, each species will adapt so that the traits that suit them best to their environments become stronger. Lower Body StrengthДЄll types of species have different strengths that help them adapt to their environment. They have discovered the difference in muscle architecture between chimps and humans. Researchers believe that the chimpanzee is about four to five times stronger compared to humans.

Chimpanzee hand anatomy