Lateral lunges help to improve single-leg strength and stability, as well as ankle mobility. Exercises that involve moving to the side while lunging down - like the lateral lunge requires coordinating the muscle activity as you lunge and step to the side. Lateral lunges move the legs in the side-to-side direction, also called the frontal plane. The lunge movement moves the legs in the front-to-back plane, also called the sagittal plane. A movement that involves more than one joint and moving in more than one plane is considered to be more functional because they are more like everyday activities. 

It seems like the majority of leg exercises involve moving the legs forward and backward. It is true that the muscles on the front and back of the legs are much larger than the muscles on the inside and outsides of the legs. And, we do spend more of our day moving in the front-to-back (sagittal) plane of motion. But, it is important to understand that the leg muscles have to work together in coordination to stabilize the pelvis, hip, knee, and ankle joints during all upright activity. In order to be able to do this, the muscles need to be balanced. Strengthening the muscles on the front and back of the legs and not doing anything for the muscles on the inside and outside can create imbalances. The muscles that are worked more, will be too much stronger than the ones that are not. For example, doing quadriceps exercises all the time and never including exercises to strengthen the hip abductors. This could result in the knee collapsing inward when you do forward lunges. The muscles on the side of the hip need to be strong enough to hold the thigh in good alignment in standing and when the knee bends. A well-designed exercise program includes addressing all of the muscle groups. This way the muscles will be more evenly strengthened, and they will be able to work together in coordination, each group capable of doing its job. 

With age, the joints of the hips and ankles get stiff and the leg muscles get weaker. The two things, joint stiffness and muscle weakness feed off of each other. When a joint is stiff, the muscles will not get used as much, when the muscles are not used as much, they get weaker and don’t move the joint as much, and the joint will get stiffer. And the reverse can also happen, the muscles get weak, the ankle does not move enough so it gets stiff, and the stiff joint leads to less muscle activity and weakness. This leads to a slowly progressive loss of function. Joint stiffness and leg weakness change the way we move. This can be seen when you watch older people move. They tend to walk slower, flat-footed, and with shorter steps. When they get out of a chair, they tend to lean their weight forward and push up with their hands. Over time, the leg muscles get weaker and the ankle, knee, and hip joints get stiffer. The trend continues, eventually leading to aches and pains in the back, hips, knees, and ankles, and declining function. The good news is that this process can be slowed down with exercises like lateral lunges. The lateral lunge bends the ankle more than forward lunges and uses muscles on the inside and outside of the entire leg, including the ones that cross the ankle which are very important for balance, and stability.