Bipedal posture allows quadrupeds to strike downward rather than upward on an opponent.
Bipedality also facilitates striking downward which can impart more than 200% more energy than is possible when striking upward.
Because striking downward requires concentric activity from the retractor muscles of the forelimbs whereas striking upward requires concentric activity from the smaller protractor muscles, quadrupeds may be able to do more work on an opponent when they strike downward.
In summary, humans are capable of striking with greater force and energy from bipedal than quadrupedal posture and can impart much more energy when striking downward than upward.
When striking downward and upward, subjects did 44 and 47% more work respectively when they performed from bipedal than from "quadrupedal" posture (Table 1).
Striking downward may increase the power of the limb because limb retractor muscles have a greater capacity for positive work than limb protractor muscles.
The magnitude of the greater energy imparted in downward directed strikes suggests that the most important reason quadrupeds stand bipedally to fight is that it allows them to strike downward on an opponent.
I used a one-sided test for significance given the hypotheses that bipedal posture would be more effective than quadrupedal posture and that striking downward would result in more powerful recordings than upward strikes.
The results of this study indicate that humans are capable of striking with 40 50% higher force and energy from bipedal than quadrupedal posture and can impart more than 200% greater energy when striking downward than upward.
Although larger size (i.e., body mass) provides an advantage during physical competition, the results of this study suggest that greater height, by itself, is associated with an enhanced capacity to strike downward on an opponent.
