Open water swimming

Shapely legs: Breaststroke - often favoured by open-water swimmers - means the lower-body muscles do the lion's share of the work, giving the leg muscles a challenging workout. 4 stars

Weight loss: Not as good as you may think, possibly because it increases appetite: research found that swimmers gained an average of 2.2kg (5lb) when put on a three-month exercise programme for weight loss. 2 stars

Cardiorespiratory fitness: Professional swimmers use 50% less oxygen - so they're better at conserving their breath - to achieve the same speed in front crawl as untrained swimmers. 5 stars

Upper-body strength: Around 80% of the work in front crawl is performed by the back, shoulders and arms. The upper body is taxed less in breaststroke, but the muscles still work continuously. 5 stars

Convenience: An accessible sport, but not something you should do on your own - it's important to check that the water is safe before you take the plunge. Hypothermia is also a risk. 2 stars

Scuba diving

Shapely legs: Swimming with fins (flippers) is like water-based weight-training - firming the front of the thighs as you kick down and the back of the thighs as you kick up. 4 stars

Weight loss: Surprisingly good for burning energy. Someone weighing approximately 70kg (11st) burns 13 calories a minute while scuba diving, so a 45-minute dive would use 585 calories. 3 stars

Cardiorespiratory fitness: According to the British Thoracic Society, scuba divers tend to have larger-than-average lungs and an increased vital capacity (the maximum volume of air exhaled after inhalation). 4 stars

Upper-body strength: The back, shoulders and arms get a certain amount of work lugging around equipment, but once in the water, the upper body gets off lightly. Arms are usually folded across the chest or kept by the sides. 2 stars

Convenience: Even if you decide to dive in the UK, it's still an equipment-heavy, location-specific, expensive sport that requires a licence, and therefore tuition. 1 star