Oh Ha-young shows off toned bikini figure — what happens to your body when you swim and play tennis?

Oh Ha-young of the K-pop group Apink has drawn attention after sharing photos of her toned bikini figure. Known for regularly swimming and playing tennis, she has sparked interest in the combined health benefits of pairing two physically distinct sports.

Oh recently posted several photos on her SNS with the caption, "My first and last vacation and swim of the year."

The photos show her enjoying a poolside holiday in a bikini, her lean, well-defined physique drawing considerable attention.

Beyond swimming, Oh is known to stay active through hobbies such as tennis. Both sports engage the whole body, but the physical demands they place on it differ considerably. Swimming builds cardiovascular endurance while minimizing stress on the joints, whereas tennis — with its bursts of sprinting, sudden stops and sharp changes of direction — delivers intense stimulation to the lower body and bones.

Swimming works the entire body against water resistance and can help manage body fat.

Swimming is a quintessential full-body workout, engaging not only the arms and legs but also the core muscles needed to maintain posture.

Because water offers far greater resistance than air, the muscles must work continuously with every stroke and kick. The sustained, repetitive movement also raises the heart rate, providing an aerobic workout at the same time.

Swimming can also help with body composition. A meta-analysis pooling data from 20 aquatic exercise studies involving 565 healthy adults found that participants who exercised in water tended to lose body weight, fat mass and body fat percentage while gaining lean mass and skeletal muscle mass. The effects were most pronounced when moderate-intensity or higher exercise was sustained over a set period.

A large-scale systematic review published in 2024, which analyzed sports and health research covering more than 2.6 million adults, also linked swimming to improvements in body composition and blood lipid levels.

Swimming does not, however, cause fat to disappear from any specific area. Spot reduction — targeting fat loss in a particular zone such as the abdomen or thighs — is not how the body works. Fat loss occurs across the body as a whole through consistent exercise and a balanced diet, and changes in body shape follow from there.

Swimming is easy on the knees, but its effect on bone density may be limited.

One of swimming's greatest advantages is the relatively low impact it places on the joints.

In water, buoyancy supports part of the body's weight, reducing the shock transmitted to the knees and ankles compared with weight-bearing activities such as running or jumping, where the full force of landing travels directly through the joints. This makes swimming a sound choice for people who find weight-bearing exercise difficult or who are returning to exercise after a long break.

Yet that same quality can also be a limitation.

Bones maintain their density by adapting to the stress of bearing weight and absorbing impact. Because the body is relatively shielded from gravity in water, many studies have found that swimming alone does not produce a meaningful increase in bone density.

A study published in 2024 found that competitive swimmers' bone density in the lumbar spine and hip joints was broadly similar to that of sedentary controls. Earlier research has also consistently shown that swimmers tend to have lower bone density than athletes who engage in high-impact activities such as running or jumping.

For those who swim as their primary form of exercise, it is advisable to supplement with weight-bearing land activities — such as strength training, brisk walking or stair climbing — that load the bones.

Tennis fills the gaps swimming leaves behind.

Tennis, which Oh also plays regularly, delivers a very different kind of physical stimulus from swimming.

A tennis match involves constant repetition of short, explosive sprints, sudden stops and rapid changes of direction. These movements engage not only the lower-body muscles — the thighs, glutes and calves — but also the core muscles responsible for balance.

When swinging a racket, power generated in the lower body travels through the rotation of the torso to the shoulder and arm. Tennis is far more than an arm sport; it effectively engages the body's entire kinetic chain.

The weight-bearing nature of tennis and its repeated directional changes also apply mechanical stress to the bones. Studies analyzing tennis players have found that the dominant arm — the one that repeatedly swings the racket — has higher bone mineral content than the non-dominant arm, a result interpreted as the skeleton adapting to long-term, repetitive mechanical loading.

In short, combining swimming — which builds cardiovascular endurance and whole-body muscular endurance with minimal joint stress — with tennis, which demands weight-bearing movement and quick footwork on land, allows the body to receive two distinct types of physical stimulus.

Building a toned physique still requires strength training.

Swimming and tennis alone do not cover every aspect of fitness.

Preserving muscle mass is essential for reducing body fat while maintaining a toned physique. Drastically cutting food intake while doing excessive aerobic exercise can cause the body to lose muscle alongside fat.

Adding lower-body exercises such as squats, lunges and hip bridges, along with upper-body strength work such as rows and push-ups, at least twice a week can compensate for the strength stimulus that swimming and tennis alone may not fully provide.

Adequate protein and carbohydrate intake, along with sufficient recovery time between sessions, are equally important. High training volume without enough food and rest can impair performance and raise the risk of injury.

Tennis carries specific injury risks: the sport's repeated sharp changes of direction can cause acute injuries to the ankles and knees, while the constant repetition of serves and groundstrokes can build chronic strain in the shoulder and elbow. Research on tennis injuries consistently shows that acute injuries tend to occur in the lower body, while overuse injuries from repetitive motion are more common in the upper body.

For those just starting out, it is better to first learn proper footwork and swing mechanics and gradually increase training volume, rather than jumping straight into long matches.

Building a toned body does not require finding a single "best" exercise. Combining low-impact aerobic work like swimming with a weight-bearing, agility-demanding sport like tennis — and rounding it out with strength training — allows the cardiovascular system, muscles and bones to be challenged in complementary ways.