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

[120 total points] (public health) in one of the largest human experiments ever conducted, in 1954 a randomized controlled trial was run to see whether a vaccine developed by a doctor named jonas salk was effective in preventing paralytic polio. a total of 401,974 children (ages 6–9), chosen to be representative of those who might be susceptible to the disease, were randomized to two groups: 200,745 children (the control group c) were injected with a harmless saline solution (a placebo) and the other 201,229 children (the treatment group t) were injected with salk’s vaccine. what was the point of giving saline solution to the children who didn’t get the vaccine? explain briefly.