Running and tennis are both sports that depend heavily on use of the feet, but the way the feet are used in each sport is significantly different. Having appropriate footwear specific to each sport is critical.
The American Orthopaedic Foot & Ankle Society suggests buying your athletic footwear at a specialty store at the end of the day when your feet have swollen to their largest. Bring a pair of socks you would normally wear with your running or tennis shoes. Once you try on a pair, walk around the store for 10 minutes or so.
Comfy Cushion and Support
The design of running shoes supports, stabilizes and cushions your feet. When you run, you tend to go in one direction, forward. Running shoes are designed to help the body cope with the rigors of running.
Running shoes have cushioned toe and heel areas to reduce impact from heel-to-toe strikes on the ground. While there is some lateral stability built into running shoes, it is usually very little because side-to-side motions are uncommon in running.
Cushioned shoes are also called "neutral" shoes according to American Academy of Orthopaedic Surgeons. They're fashioned for people with high arches. Stability running shoes are for those people whose arches may collapse. Heavier people and people with flat feet should choose motion control running shoes.
Lateral Support and Stability
Tennis shoes are specifically designed for use on the tennis court. Whereas the running shoe places emphasis on cushioning, tennis shoes focus on lateral support and stability. Lateral support and stability is crucial to tennis players, as many of the quick movements executed on the tennis court are side-to-side cuts, rather than heel-to-toe running.
While cushioning is important to the tennis player, it is less important than lateral stability and a low to the ground feel. The lower a player's foot is to the court, the more stable it will feel laterally. Because of this necessity for lateral stability, cushioning in tennis shoes is less than running shoes.
Every Ounce Counts
Excess weight on a runner's feet make her slower. Every ounce of weight counts when it comes to running. Tennis shoes also strive to be lightweight, but not at the expense of durability and support.
Light, cushioned, flexible running shoes tend to weigh less and be more comfortable than durable, supportive, stiff tennis shoes. While many people wear running shoes casually because of their comfortable feel, it is unusual to see people wearing tennis shoes casually.
Sole and Durability
Tennis and running shoe soles differ considerably. Running shoes are often discarded when they lose their cushioning or spring, but rarely because of holes in the shoe. The American Heart Association suggests replacing your runners when the tread is worn down; and that's typically after 350 to 500 miles of running.
Tennis shoes are usually discarded when the player wears through the outsole or grinds down the sole until it is smooth and offers little traction. Tennis shoe soles are made to be considerably more durable than running shoes. The constant stopping, starting and sliding of tennis puts substantial strain on the durability of the sole.