NEW YORK (Reuters Health) - Women who did a high-intensity aquatic workout for six months increased their strength and suffered fewer falls, in a new study that suggests bone- and muscle-building resistance can be achieved with the right kinds of water exercises.
"What we did was to test the model for muscle training in the gyms and put it inside the pools," said lead author Linda Moreira, a researcher at the Universidade Federal de São Paulo.
The study should encourage postmenopausal women at risk for osteoporotic bone-thinning that pool-based exercise can increase muscle and bone strength, according to Moreira's team.
Aquatic aerobics became popular in the 1990s as a way for older people to exercise without straining their joints or being injured in falls.
However, aquatic exercise fell out of favor, experts said, because of concerns that the bone and muscle-building benefits of resisting gravity in standard exercises were diminished when someone is buoyant in water.
To test a water workout Moreira's group designed to increase resistance and build strength, they recruited just over 100 inactive women in their 50s and 60s.
All the women took 1,000 international units of vitamin D3 and 500 milligrams of calcium daily - both vitamins known to help build bone and muscle - during the six-month study.
Half the women were also assigned to an aquatic exercise program, which Moreira's group created to combat osteoporosis by preventing falls, and named HydrOS.
Instead of the more typical high-repetition, low-impact aqua-aerobics, the HydrOS interval training included bursts of intense activity between 10 to 30 seconds at up to 90 percent of maximum heart rate. The water created the resistance that weights would provide on land, Moreira said.
Seven months later, the number of falls among aquatic exercisers had dropped 86 percent, and the number of women who suffered falls dropped 44 percent. In the sedentary group, the number of falls remained unchanged, according to results published in the journal Menopause.
The researchers also found that flexibility plus hand, back, hip and knee strength increased in the aquatic exercisers. The women in the sedentary group showed mild increases in balance and strength as well, but the researchers attributed those improvements to the calcium and vitamin D supplements.
As people age, they lose muscles used for quick movements that stimulate bone health. But, according to Moreira, typical aquatic aerobics work muscles used for slower day-to-day movement.
"Physical instructors were training the wrong muscle type," she said.
About a quarter of the study participants had osteoporosis, half were at the beginning stage of the bone disease and the remaining quarter had normal bones.
"There's this bias in the osteoporosis community against doing any water-based exercise," said Andrea LaCroix, a researcher at Fred Hutchinson Cancer Research Center, who studies health in older women. LaCroix was not involved in the current study.
"This study goes in the face of that," LaCroix told Reuters Health. "If they show changes in bone density, that would be quite amazing and novel and will be a paradigm changer in terms of osteoporosis prevention."
Moreira told Reuters Health that another soon-to-be-published paper will show that over the six months of the study, the aquatic exercise group maintained bone mineral density in their femur leg bones while the sedentary women lost 1.2 percent of bone density.
Very little is known about how water exercise can improve health in older adults, said Wendy Kohrt, professor of medicine at the University of Colorado School of Medicine. Kohrt was not involved in the current study.
"Without knowing what the benefits are, it's difficult to recommend water exercise; (the study) fills a gap in knowledge that is a pretty big gap," Kohrt added.
"Improvements tended to be small (with the aquatic approach). It's a little difficult to judge just how effective this type of exercise program is," Kohrt told Reuters Health.
Kohrt noted that one serious limitation of the study was that researchers didn't use equipment that could maximize muscle resistance.
"There are ways to use devices in water to make it a more effective strength training approach," Korht said, such as moving a milk jug or webbed object through the water.
"The next step is to find out whether water exercise can be as effective as more traditional land-based types of exercises," Kohrt said.