Answer
Energy is expended when a muscle-tendon complex contracts and recovered when it relaxes. The faster pace requires more energy, as it requires the same amount of energy for the motion but less is recovered due to the lack of energy recovery from relaxation in between, making the total energy cost higher.
Work Step by Step
For the longer interval:
$735j/s-159j/s=576j/s $
$576j/s \div 1.85h/s=311j/h$
For the shorter interval:
$716j/s-159j/s=557j/s$
$557j/s \div 0.92h/s=605j/h$
