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

During very difficult workouts, you work hard and breathe heavily.
What should the words in italics be replaced with to make this sentence more precise?
High frequency
Low intensity
High intensity
Low frequency