Researchers found in a study comparing sedentary adults in their 60s and 70s with those in their 20s and 30s, that older men and women had to use much more oxygen to walk at the same speed as their younger counterparts.

But after taking up a six-month exercise program involving walking or jogging, biking and stretching, the seniors reversed their loss of exercise "efficiency."

The term exercise efficiency means how much energy the body expends to perform a given activity.

Dr. Wayne C. Levy of the University of Washington in Seattle, the study's senior author, says at the start of this study, the seniors in the group used 20 percent more oxygen to walk at the same speed as a younger person.

But after six months of regular exercise, 90 minutes, three times a week the older participants' exercise efficiency improved by 30 percent, versus only 2 percent among their younger counterparts.

It is common knowledge that as people age, there is a decline in the exercise or work a person can do before becoming exhausted.

The new findings suggest however that this is not just a product of the aging cardiovascular system being less able to send oxygen to working muscles, but that the older body also needs more oxygen to perform the same work as a younger one i.e. exercise efficiency declines.

But this decline appears to come about mainly through inactivity, and may very well be reversible.

Dr. Levy says the idea that exercise efficiency dips with age is a "relatively new concept," and although younger people in his study were still better at pumping blood and oxygen to their muscles after exercise training, it was only the older exercisers who showed significant gains in exercise efficiency.