Strength versus Endurance

Continuing on with our journey into understanding the exercise science of weight training, we want to direct our attention toward building and sustaining muscle through strength and endurance training.  First let’s review the definitions of muscular strength and endurance.  Muscular strength is the ability of the muscle to generate maximum force over a short period of time.  Training for muscular strength usually requires high weight and a low number of reps.  Muscular endurance is the ability of the muscle to generate force over a period of time.  The opposite occurs if you are endurance training; the weight is low and the numbers of reps are high.  We all agree that we need both strength and endurance in our daily lives in order to function effectively and efficiently.  Muscle tissue consists of fibers that generate contractions for motion, posture and heat production.  Muscle tissue is classified into three categories:

1)  cardiac - which are the involuntary heart muscles;
2)  smooth - which are located in the internal structures like the blood vessels, stomach and bladder;
3) skeletal - which are attached to the bones and creates movement.  These skeletal muscles vary with respect to metabolic processes they use to generate adenosine triphosphate (ATP).

Our anaerobic exercise training focuses mainly on the skeletal muscles.   Skeletal muscle fibers can be classified as either slow twitch or fast twitch.  Before we get into the different specific ways to overload the muscle, we want to explore the impact of fast twitch and slow twitch on exercise.  Most of us are born with about 50% of each type of fiber.  In extreme cases like an Olympic sprinter or international marathoner, there is a definite genetic predisposition toward having more of one or the other.  Science has shown us that we cannot significantly increase or decrease the numbers of specific muscle fiber types but that they can be anaerobically trained, especially the fast twitch fibers to increase muscle conditioning. 

Slow twitch or slow oxidative fibers contain myoglobin (an oxygen binding protein found in skeletal muscles), many mitochondria (powerhouses of the cell) and many blood capillaries. These fibers are red, split ATP at a slow rate and have a slow contraction speed.  They are as also very resistant to fatigue.  There are a lot of these fibers found in the postural muscles.  Athletes that have a higher proportion of slow twitch fibers will excel more easily in endurance events such as marathons and cycling in events like the Tour de France.

The fast twitch or fast oxidative fibers can deliver more powerful and faster burst of energy. However they fatigue faster than the slow twitch fibers.  They contain very large amounts of myoglobin, very many mitochondria and very many blood capillaries.  These fibers are white and have a high capacity to generate ATP by oxidative metabolic processes.  These fast twitch fibers split ATP at a rapid rate and contract fast.  Most skeletal muscles contain both but their proportion varies depending on the usual action of the muscle.  Strength type of activities like weight lifting and sprinting place a demand on the fast twitch fibers and require immediate and fast contractions.  Runners like Michael Johnson and Usain Bolt probably have a greater proportion of fast twitch fibers compared to slow twitch.  Fast twitch fibers have a great capacity for improvement through appropriate training.

Since we are focusing our conversation on strength and endurance training we will be recruiting all the muscle fibers with an emphasis on one or the other depending on high weight and low reps or low weight and high reps. 

Obviously, success in anaerobic conditioning endeavors is a combination of correct training procedures while in the gym; correct diet or food fueling; and proper support from non-food fueling or supplementation.  If you do not recognize the importance of all three of these areas, get ready to accept failure.