The following will likely only be of interest to older runners,walkers, cyclists and folks who like to talk about mitochondria.see here for a interesting commentary about muscular efficiency,aging and its effect of various kinds of exercise.
The mainstream current party line regarding the determinants of endurance exercise performance is that the major three factors are:
1Maximum oxygen uptake ( V02Max)there are conflicting data regarding whether regular endurance training over the years lessens that decrease with the older data supporting that idea.More recently Tanaka and others have shown that when expressed as per cent decrease from early adulthood, the rate of decline in VO2Max is not reduced in habitual aerobic exercisers.See page 58 reference no. 1.
2)Lactate threshold (LT).LT as a measure of the exercise intensity at which a person can sustain a high level of the maximal oxygen consumption.It is said to decrease with aging.Although data indicate that the absolute work rate or running speed at the LT decreases as a function of age, the LT does not change when expressed as a percentage of the 02 Max. Tanakia and Seals (ref 1) suggest that the decrease in LT is secondary to decreases in the 02Max.
3)Exercise economy .This is measured as the steady-state 02 consumption while exercising below the LT.A number of cross-sectional studies have shown that exercise economy does not change with aging.Most of the studies were done in runners but now we have a study that demonstrates a decrease in excise efficiency in cyclists with aging.
Alex Hutchson in his Runner's World column,"Sweat Science", discussed several articles that demonstrated that older cyclists became less efficient with age but that deficit compared to the younger cyclists was abolished by a several week period of quadriceps resistance exercises . In one study a 3 week training period increased leg strength by about 18% and cycling efficiency by about 16%. Possibly the old high school coach's comment "you are only as young as your legs might really be "you are only as old as your quads".Aging runners and cyclists can profit by adding quad resistance exercises to their exercise program.
As early as the 1980s there was experimental evidence that resistance exercise could increase mitochondrial bio-genesis and improve oxidative capacity even in a person habitually doing endurance exercise.
1)Tanaka,H and Seals DR, Endurance exercise performance in masters athletes.
J Physio 586 1 (2008) pp 55-63
5/25/16 minor additions made regarding quadriceps exercise.