An interesting study suggests you don't have to spend hours at the gym to see significant benefits (Gillen JB, et.al., 2016).
The study compared traditional moderate-intensity continuous training, which involved 50 minutes of continuous exercise, with sprint interval training, which took just 10 minutes per session. The participants used a stationary bike.
The all-out cycle sprints involved 3, 20 second sprints with 2 minutes recovery in between with very slow cycling. Both groups exercised 3 times a week.
After 12 weeks, both groups showed a 19% improvement in peak oxygen uptake and similar gains in insulin sensitivity. Interestingly, the sprint interval training group achieved these results with five times less exercise volume and time commitment. So, even a quick, intense workout can be effective for better health.
Jenna B Gillen 1, Brian J Martin 1, Martin J MacInnis 1, Lauren E Skelly 1, Mark A Tarnopolsky 1 2, Martin J Gibala 1. Twelve Weeks of Sprint Interval Training Improves Indices of Cardiometabolic Health Similar to Traditional Endurance Training despite a Five-Fold Lower Exercise Volume and Time Commitment. PLoS One. 2016 Apr 26;11(4):e0154075.