Core
The core is one of the most unappreciated but important parts of the body to exercise. It is composed of your abs, your hips and your back. A strong core may increase your speed.
The core controls the functions of walking, running, bending down, and sitting up in the morning. Your core goes hand-in-hand with your cardio; a long distance runner needs a strong core to sustain a two-mile run. When you first start working out your core, you will notice an immediate difference in the way you breathe; short breaths will do you no good. You will learn to expand the lungs in order to take in more oxygen.
Here is what Elizabeth Quinn from About.com has to say about core programs:
"The best core exercises may surprise you. It's not enough to just do ab crunches and sit ups. To build a strong core you need to exercise a variety of muscles from your hips to your shoulders. Most people think of the core as a nice six-pack, or strong, toned abs, but the truth is that the abdominal muscles are a very small part of the core. The abs have very limited and specific action, and what experts refer to as the "core" actually consists of many different muscles that stabilize the spine and pelvis, and run the entire length of the torso. When these muscles contract, they stabilize the spine, pelvis and shoulder girdle and create a solid base of support. When this happens, we are able to generate powerful movements of the extremities.
The core muscles also make it possible to stand upright and move on two feet. These muscles help control movements, transfer energy, shift body weight and move in any direction. A strong core distributes the stresses of weight-bearing and protects the back. Core conditioning exercise programs need to target all these muscle groups to be effective."
Cardio
If you have not included some kind of cardio in your workouts, you are not working out successfully. Cardio increases the heart rate and works out the heart, the strongest muscle in the body.
Cardio is a full body exercise unlike some weight exercises that just target specific areas. Cardio works out your legs, arms, heart, lungs and many more things. Cardio breaks down the bad sugars and fats in the body and turns them into lean muscle. Cardio is essential whether you're trying to lose weight, gain weight, or tone muscles.
Here is what Jeremey DuVall from Muscle & Fitness has to say about cardio:
"Cardio often comes up as a buzzword in the fitness industry, demonized by anyone looking to gain muscle. Doing aerobic work is seen as a step backwards as opposed to adding in another lifting session. In reality, some sort of cardio training is necessary in any program. However, the duration and intensity of the sessions should be dictated by training goals and aspirations. Someone looking to increase their powerlifting total has far different demands than the weekend warrior looking to attempt their first marathon. No matter the goal, there are smarter and more efficient ways to work your cardiovascular system without compromising your entire weekend.
Many guys in the gym lack specificity within their cardio program. When it comes to lifting weights, they have detailed notes of sets, reps, personal records, and arm growth progressions. For cardio, they slough off the numbers and progressions in favor of 20-30 minutes at a moderate intensity. Your cardio training should be approached with the same precision and details as a well-executed weight training program. By paying closer attention to intensity levels and duration, gym-goers can reap the benefits of an intense session without wasting away their day slogging miles on the treadmill."