An adapted sprint interval training protocol involving 2-3 repeated 20-second sprints separated by 2-3 minutes rest (termed reduced exertion high- intensity interval training (REHIIT)) has been developed and has been shown to promote fitness benefits. This data shows how little exercise one may need to improve cardiorespiratory fitness, provided they are willing to work very hard. However, it is unknown whether the benefits of REHIIT are because of the "all-out" nature of the sprint efforts themselves or the pattern of completing sprints with relatively short (i.e., minutes) rest periods within a workout session.

We are inquiring whether performing the same number and style of sprints with prolonged rest (i.e., 1-4 hours of rest in between sprints) is equally effective for improving aerobic fitness when compared to more traditional sprint interval training with 2-3 minutes of rest between sprints. Such information may make the effectiveness of sprint training more accessible and approachable for individuals unwilling or unable to plan a purposeful REHIIT exercise session into their day. If the rest interval could be prolonged then it may be possible to perform a few sprints as "exercise snacks" throughout the day without the need for a structured interval training session.

Inclusion Criteria:

• Physically inactive (2 or less bouts of purposeful exercise per week)

Exclusion Criteria:

• If your doctor has informed you that you have a heart condition and should only do physical activity recommended by a doctor.
• If you feel pain in your chest when you perform any physical activity.
• If in the past the month you have had chest pain when you were not doing any physical activity.
• If you lose your balance or consciousness because of dizziness.
• If you have bone or joint problem (for example, back, knee, or hip) that could be made worse by a change in your physical activity.
• If you are currently pregnant or planning on becoming pregnant in the next 6 weeks.
• You have previously had a heart attack or stroke
• You are currently engaging in high-intensity interval training.
• You are currently physically active (engaging in 3 or more bouts of purposeful exercise per week; a "bout" is defined as structured, planned exercise lasting at least 30 minutes)
• You have severe chest pain or blood pressure over 240/140 during baseline testing.
• You have exercise induced asthma or a history of syncope.

Individual data will be shown in all manuscript figures

Participants will know what exercise group they are assigned to.