Biomechanical and physiological measures of running performance were obtained for 31 subjects running at 3.57 m·sec⁻¹ in order to describe the relationship between mechanical aspects of running style and physiological efficiency. Sub-maximal oxygen consumption while running on a treadmill at the test pace was used to establish the range of variability found among subjects in physiological efficiency. Three-dimensional cinematography techniques were employed to provide measures of the kinematics of overground running which were used in the calculation of mechanical work rates. Additional biomechanical parameters measured for both right and left strides included ground reaction forces and center of pressure patterns, stride lengths, and foot crossover during support. Data were also obtained for maximal oxygen consumption, muscle fiber composition, and the ability to store and re-use elastic energy while performing kneebends for each subject.

Mechanical work rates were calculated using a segmental approach as well as for the center of mass alone. Complete within segment energy transfer was assumed in the segmental approach and four progressively restrictive conditions of between segment energy transfer were derived for use in the determination of positive mechanical work rates. The different metabolic cost of positive and negative work was accounted for by adding one-third of the total negative work rate to the net positive work rate to give a measure designated the metabolic equivalent work rate.

Through comparisons of mechanical work rates with physiological efficiency it was determined that the total cycle mechanical work rate as well as energy transfer among all segments of the body were Important factors affecting physiological efficiency. Runners who had low metabolic equivalent work rates generally showed greater energy transfer and lower submaximal oxygen consumption. The greatest amount of energy transfer occurred during the time period from just before toe-off to just after heel strike. A multiple regression analysis identified several factors, including net positive work rate, that predicted physiological efficiency well.

The metabolic equivalent work rate for complete between segment energy transfer was 532.1 watts. This value was compared to work rate values of 557.8 watts calculated using the tdtal transfer method of Winter (1), 1775.1 watts for the psuedo-work method of Norman (21), and 475.2 watts for the center of mass alone. A mean efficiency ratio for all subjects of 0.59 was calculated. It is argued that physiological or mechanical work rates by themselves are of greater practical importance than the efficiency ratio.

No trends were seen for maximal aerobic capacity, muscle fiber composition, or elastic storage of energy with relation to physiological efficiency. For kneebends, elastic storage and re-use of energy accounted for a mean 24 percent savings in metabolic energy.

Mechanical efficiency, as determined by the metabolic equivalent work rate, was closely related to changes in vertical movement of the center of mass as well as to changes in the velocity of the center of mass. Various other kinetic and kinematic parameters were also found to be significantly related to mechanical efficiency. It is concluded that mechanical work rate is an important factor affecting physiological efficiency and that energy transfer is the most.important parameter affecting mechanical efficiency.