Trey's family has been walking together for 20 minutes at least three days per week for the past four weeks. they already have so much more energy, and they want to continue to improve. how could trey's family apply the fitt principles to make their walking routine more effective?

add push-ups to their routine
replace one walk with a bike ride
add an extra day of walking each week
wear new shoes to walk faster

According the FIIT principles, in order to make their routine more effective they need to increase the frequency, intensity, time and type of exercise that they are doing. In the particular example cited here, they might add one extra day of walking in the following week to up the frequency of their exercise. Once they become used to more exercise, they might then add alternative forms of physical fitness into their routine.

Bis the right answer