Though the study is interesting and a useful one, here are some comments on whether this study applies to you:
1. Who Does the Study Apply to?
The subjects, as mentioned above, were sedentary (i.e. non-exercising) women between the ages of 60 and 74. Would the study have produced the same results with a group of 20-year-old undergraduate phys ed students? My suspicion is no. Don't get me wrong—we've based our exercise recommendations on studies of undergraduates for far too long, so it's great that this study was performed with older women. But let's not overgeneralize the conclusions. What's "too much" for one group of people is definitely not the same for other groups.
2. Over What Time Period Does the Study Apply?
The study lasted 16 weeks, which is actually pretty good for this type of study. Still, what would have happened had it lasted five years? Would the conclusion that the different regimens produced "almost no difference in fitness gains among the groups" still have applied? Again, I suspect not: two workouts per week might have been ideal for sedentary beginners—but then again, just about ANY fitness routine produces gains in sedentary beginners. It's more difficult—and may require more workouts—to continue to improve after you've taken the low-hanging fruit.
3. Does Time Commitment Matter?
The researchers started the experiment with the hypothesis that six workouts a week would overstress the subjects and leave them fatigued and overtrained. To verify this, they measured stress markers in the blood (cytokines) as well as subjective measures of fatigue and vigor. To their surprise, the six-workout group didn't seem overstressed at all—they had the same values as the other groups. The big difference, the subjects reported, was that the six-day routine was extremely time-consuming. They had to commute to the lab six times a week, and then spend 50 minutes (including the workout plus warming up and so on) for each session. As a result, they felt busy and short on time, and consequently spent less time being active outside the workouts.
This is actually a very important insight. A crucial part of a workout plan's effectiveness is how convenient it is, and how smoothly it fits into your life. Time is valuable, and minor hurdles like having to hop in the car to get to your gym can become major hurdles when you're busy or stressed or simply tired.
All of which is to say that: yes, this study offers an interesting take with great relevance to sedentary older women who want to start exercising. And it has relevant messages for the rest of us too—but that doesn't mean the message is "you should only exercise 2 to 4 times a week to maximize your benefits."
Stay in shape in a fitness class.