Can exercise be optimized in any meaningful way for the average, basically healthy individual? Can you dig through the research literature and, based on what you find, be fairly certain that you should exercise for an hour daily rather than half an hour, or run rather than use a rowing machine, or make some other similar adjustment to your schedule of moderate regular exercise? At this point, I think that the answer remains a qualified "no."
Research strongly supports moderate exercise over no exercise. You are absolutely doing yourself harm by being sedentary. After that the data becomes a lot more malleable and less certain. The research community can't say for sure whether athletes are benefiting over the long term from all the additional exercise they do, for example. Professional athletes appear to live modestly longer than the general populace, but there's no convincing demonstration that this is because of what they do versus being the results of a selection effect based on the fact that you have to be unusually robust to succeed as a professional athlete.
For the rest of us, in our considerations of jogging versus exercise bikes, much of the data gathered doesn't reliably support any choice over another once you've made the basic, essential decision to undertake regular aerobic exercise. The waters are muddy, however. In the past few years, large studies have emerged to confirm that time spent sitting appears to raise mortality rates and lower life expectancy regardless of exercise taking place in between those seated periods. See this, for example, although the publicity materials don't make it terribly clear that thought did go into the causality of the effect:
Compared with those who reported sitting four hours or less per day, those who sat for more than four hours per day were significantly more likely to report having a chronic disease such as cancer, diabetes, heart disease and high blood pressure. The reporting of chronic diseases rose as participants indicated they sat more. Those sitting for at least six hours were significantly more likely to report having diabetes.
Researchers said that although most of the current evidence is suggestive of a causal connection, they cannot be certain in this study whether volumes of sitting time led to the development of chronic diseases or whether the chronic diseases influenced sitting time.
Then there is the recent paper below, which might be put into much the same broad context of muddying the waters when it comes to exercise and lifestyle choices.
Minimal Intensity Physical Activity (Standing and Walking) of Longer Duration Improves Insulin Action and Plasma Lipids More than Shorter Periods of Moderate to Vigorous Exercise (Cycling) in Sedentary Subjects When Energy Expenditure Is Comparable
Epidemiological studies suggest that excessive sitting time is associated with increased health risk, independent of the performance of exercise. We hypothesized that a daily bout of exercise cannot compensate the negative effects of inactivity during the rest of the day on insulin sensitivity and plasma lipids.
Conclusions: One hour of daily physical exercise cannot compensate the negative effects of inactivity on insulin level and plasma lipids if the rest of the day is spent sitting. Reducing inactivity by increasing the time spent walking/standing is more effective than one hour of physical exercise, when energy expenditure is kept constant.
It is tempting to leap to the thought that this sort of mechanism is needed to explain how standing versus sitting can have an effect on long-term health, but there is still much work to be done in order to convincingly knit all these statistical studies together with basic mechanisms in that way. So in the meanwhile, it continues to look like the 80/20 path is regular moderate aerobic exercise - and of course some form of calorie restriction. There's no real debate over whether or not these options are beneficial.