If the frigid temperatures and a large workload have deterred you from making a daily or weekly pilgrimage to the KSC, there is a quick, but not necessarily painless way to keep up with fitness and strength.
For 20 seconds, do as many crunches as you can, and follow this with 10 seconds of rest. Then, do as many pushups as you can for 20 seconds, followed by a 10 second rest. During the 10 second rest, stand up and get ready for the next exercise. Next, do as many jump-squats as you can in 20 seconds, and follow this with 10 seconds of rest. Then, get back on the ground during the rest and plank for 20 seconds.
Repeat this sequence four times, and you will see that not much time has passed, but your body will feel like it has done a moderately intense strength workout. If you do this once or twice a day every day for a week, you will notice that you will sleep more deeply and be more energized for class. Of course, try to go to the gym several times per week for a quality cardio workout, but when that is not possible or convenient, try the 8-minute ab blast once or twice per day.