NASA says (emphasis mine)
Current exercise countermeasures on the International Space Station (ISS) are insufficient to prevent muscle atrophy, cardiovascular deconditioning and bone loss associated with long-duration space flight. Despite crew allocation of approximately 2.5 hours per day to exercise, decrements in fitness are observed following flights averaging 180 days in duration. Muscle strength is decreased 11% to 17%, muscular endurance approximately 10% and bone mineral density 2% to 7%.
It is thus that NASA commissioned Sprint also linked in the article above
Integrated Resistance and Aerobic Training Study (Sprint) evaluates the use of high intensity, low volume exercise training to minimize loss of muscle, bone, and cardiovascular function in ISS crewmembers during long-duration missions.
What is the regimen under the Sprint program?