It is conventional wisdom to divide exercise as either strength training or cardio. It is a very simple way to classify exercise. However, this is not ideal. For decades, when most people spoke of exercise, they meant traditional, slow, long-duration exercise. Much of our basic knowledge of exercise comes from studying the physiological effects what many would call 'cardio' on our bodies. This form of exercise gained popularity in the 1970's and 1980's. However, these traditional modes of training are not the most effective, efficient or healthiest ways of developing fitness.
The Difference Between 'Cardio' and Aerobic Exercise
Cardio simply refers to the fact that the heart and lungs are utilized to support the working muscles. Simple as that. Use your muscles intensely or long enough and they will need increased blood flow. It doesn't matter if you are running, digging a ditch or deadlifting a barbell. In fact, after a set of six repetitions of heavy deadlifts ( which took ~0:30), I checked my heart rate. 175 beats per minute! My heart and lungs were utilized to a great extent to assist the working muscles. This is enough to start a physological cascade of events that will enhance my fitness and cardiovascular health.
Will deadlifting help me run better? Maybe. Here is the other side of the coin. Aerobic fitness is very specific to the movement. This is because aerobic exercise is exercise that stresses/ enhances the aerobic energy pathways in the specific muscles and muscle fibers being used during a movement. This is why Lance Armstrong is an elite cyclist, but just a pretty good marathoner (he finished the NYC Marathon in the middle of the pack). So, to answer our question, deadlifting may help your running endurance somewhat (especially if you are not very well trained. Strength training will aid running in other, indirect ways, which I will address later), but ultimately running is the best way to develop your running endurance. Aerobic conditioning is very movement specific with some carry-over to similar movements.
Traditional 'Cardio' is Not Very Efficient, Effective or Healthy
Traditional 'cardio' is extremely popular among the average gym member. In fact, people will wait in line to use one of these pieces of equipment at a typical health club. However, it is not the most efficient way to burn bodyfat, develop the best aerobic metabolic conditioning, or enhance joint function or movement efficiency.
It was thought that you need to perform long-duration (>30 minutes)exercise to enhance these aerobic energy-producing pathways because this duration of exercise derives it's energy almost exclusively from aerobic metabolism. However, more recently, researchers finally listened to coaches and trainers to test other protocols' effectiveness. Sure enough, much more effective and efficient training techniques were identified. These training techniques enhance aerobic metabolism as much or more in a fraction of the time you would spend on conventional 'cardio' exercise. But, techniques like high-intensity interval training and Tabata protocols do require effort and intensity, something that discourages a lot of people.
Running or other traditional cardio exercises come with a lot of 'wear and tear' on the body for their affect on your fitness. This is the ironic thing about cardio. People will simply start running to get in shape, not understanding that they are repetively driving forces two to three times their body weight through their joints. But, think strength training is too hard on their body. This is completely opposite. Strength training, performed correctly, can be done with less force on the joints and much more control. It also enhances the integrity of the joints, ligaments, tendons, and muscles. Repetive use injuries are extremely common among regular cardio exercisers. Most runners are nursing some injury. And their only option is to cut back for a while until their pain goes away.
Many people feel, and they have been told, that they have to do hundreds of minutes of cardio to see an effect on their body composition. But, the reality is long duration 'cardio' has a small effect on body fat. You may lose some body weight, but ultimately, nutrition and elevating your metabolism (with strength training) play the biggest role in fat loss. Additionally, a significant part of the weight loss you may experience with traditional 'cardio' is loss of muscle mass. This is because you create a catabolic, or a 'breakdown' environment with a lot of long-duration 'cardio'. High levels of stress hormones circulate in the body, which causes muscle and bone to be broken down to keep energy levels available. In contrast, a progressive strength training program with adequate recovery, produces an anabolic environment which builds muscles, tendons, ligaments, and bone density. All require energy, which comes from mostly fat. A win-win situation.
Low Intensity 'Cardio' Has Its Place.
Long-duration, low-intensity exercise can provide many health benefits for the body. Exercise, such as walking, can be done regulary and is helpful for 'actively' recovering from higher intensity exercise. The issue is, if this type of exercise is your only mode of exercise then it will be impossible to develop a high level of fitness, strength, and body composition you may desire.
Traditional 'cardio' exercise may provide some health and fitness benefits, but the impact on your strength, aerobic metabolic conditioning, muscle mass, metabolism, joint integrity, and body composition is lesser than alternative methods. High-Intensity strength training and metabolic conditioning are a more time-efficient, effective, and healthy way of training your body and should replace traditional 'cardio' or at least be your primary mode of training.