1. improved core definition and performance: 

Planks are probably one of the best, most hated abdominal exercises ever. However, they engage all major core muscle groups including the transverse abdominus, the rectus abdominus, the external oblique muscle, and the glutes. The importance of strengthening each muscle group cannot be underestimated either. Once you start to strengthen these muscle groups, you will begin to see:

• Transverse abdominis: increased ability to lift heavier weights.
• Rectus adbominis: improved sports performance, particularly with jumping. This muscle group is also responsible for giving you the renowned six pack look (Yeah!)
• Oblique muscles: improved capacity for stable side-bending and waist-twisting
• Glutes: a supported back and a strong, shapely bum

2. decrease risk of back and spinal injury

Planks allow you to build muscle without putting too much pressure on the spine or hips. Doing them regularly not only significantly reduces back pain, but strengthens your muscles and ensures a strong support system for your entire back – specially around your upper back. (See: Conquering Your Knee Pain)

3. boost your metabolism

Planks burn more calories than doing other traditional ab exercises. The muscles you activate while planking will ensure that you burn more energy even when sedentary. This is important if you are spending the majority of your day sitting in front of a computer. By making this a daily exercise before or after work, you will provide an enhanced metabolic rate, and ensure that it stays high all day long – even while you sleep! (See: 7 Metabolism Myths Busted)

4. significantly improve your posture

This exercise can greatly improve your ability to stand with a straight and stable posture. By strengthening your core you will be able to maintain proper posture at all times. This is because the muscles in your abdomen have a profound effect on the overall condition of your neck, shoulders, chest and back. (See: 6 Reasons You Should Be Wearing Wiivvs)

5. improve overall balance

How often have you stood on one leg, and realized that you couldn't balance for more than a couple seconds? It's not because you're drunk, but rather because your abdominal muscles aren't strong enough. By planking on a daily basis, you will begin to strengthen the muscles required to help keep you up right. Try side-planking and see the difference in every sport you play.

6. increase your flexibility

Ready to increase your flexibility? Planking regularly helps to expand and stretch all of your posterior muscle groups - shoulder blades, shoulders, and collarbone – while also stretching your hamstrings, arches of your feet, and your toes. Add a side plank in the mix and work on your oblique muscles. This will provide you with further benefits when it comes to hyper-extending your toes, a movement that is crucial for supporting your body’s weight.

7. increased mental benefits

Planking has a particular effect on your nerves, making them excellent for improving overall mood. This is because they stretch out all of your muscle groups that contribute to stress and tension in the body. Just think about it, you are sitting in your chair, at home or at work, all day long; your thigh muscles get tight, your legs get heavy due to being bent for several hours, and tension develops in your shoulders due to being forced to slump forward all day. The good news is that planks not only calm your brain, but they can also treat anxiety and symptoms of depression.