Toning

Aerobics: Classic class moves, such as marching on the spot, star jumps and knee lifts, focus on the calves, bottom, hips and thighs. Not so good for the upper body, though, because there's no resistance to work against.
3/5

Aqua-Aerobics: More toning potential because water has 12 times the resistance of air. Unlike gravity, the resistance exerted by water applies in both directions, so each movement works two muscle groups.
4/5

Fat burning

Aerobics: Entails nonstop cardiovascular exercise using the whole body, so it's high on calorie expenditure, although less so in low-impact classes, where one foot is always on the ground.

5/5

Aqua-Aerobics: Once seen as an easy option for the overweight and out of condition, but now believed to be a valid alternative to land-based workouts. Overly gentle aqua classes won't cut the mustard, though.
3/5

Skeleton

Aerobics: Helps to boost bone density, reducing the risk of osteoporosis. Excessive high-impact workouts, or inappropriate footwear, can cause lower leg injuries such as shin splints and stress fractures.
3/5

Aqua-Aerobics: In chest-deep water, your body weight is about 40% of that on land, so it's ideal for those with joint problems. But water's weight-bearing effect means that it won't help preserve bone density.
3/5

Pregnancy

Aerobics: High-impact is not recommended but low-impact classes are fine. A study earlier this year in the Journal of Sports Medicine and Physical Fitness found that aerobics boosted mood and energy levels.
3/5

Aqua-Aerobics: Good for physical and mental wellbeing. US research found that pregnant women who took part reported significantly less physical discomfort, and improved mobility and body image.
5/5

Balance and coordination

Aerobics: The dance-based multi-directional moves hone coordination and agility. Research from Japan found that 12 weeks' aerobic dance exercise enhanced agility and improved single leg balance time.
4/5

Aqua-Aerobics: The simpler moves involved will not improve coordination as much as aerobics. However, the supportive environment of the water is good for those with poor balance.
3/5