Our muscles give us the ability to move. We use them from the moment we wake up in the morning to the time we go to bed at night (and even in between). Throughout the day we find ourselves lifting, lowering, pushing and pulling loads as we carry out our day to day lives. Rarely do we do these movements just once or twice a day. Repetitive movements are a part of very day life and requires muscular endurance (the ability of a muscle or group of muscles to sustain repeated contractions against a resistance over a period of time).
There are generally two types of muscular endurance:
- Dynamic Endurance – a muscle’s ability to contract and relax repeatedly
- Static Endurance – a muscle’s ability to remain contracted for a long period of time
The goal of a muscular endurance program is to improve the body’s ability to contract the muscles repeatedly over an extended period of time. The body should be able to use energy more effectively while exerting force time and time again.
Although we challenge the endurance of our muscles on a regular basis (i.e. carrying a briefcase, shoveling the sidewalk, scrubbing the bathtub or raking leaves) workout programs tend to focus on developing muscle size and strength. The likely cause of this is a lack of knowledge and understanding as to how muscles work and how they adapt to different types of weight training programs.
Understanding Muscle Fiber Type
The human body is made up of 430 muscles. Skeletal muscle is made up of two types of muscle fibers:
- Slow twitch muscle fibers (Type I)
- Fast twitch muscle fibers (Type IIa, IIb)
On average, humans have about 50% slow twitch and 50% fast twitch fibers in most of the muscles used for movement. This is determined at birth and, no matter how much we exercise, we can’t change the amount of slow or fast twitch fibers in our muscles.
The smaller, slow twitch fibers are better suited for continuous, extended muscle contractions that go for a long period of time. These fibers fire more slowly than fast twitch fibers and can go for an extended period of time before they fatigue. This is because they are more efficient using oxygen (and fat stores) to generate fuel to feed the working muscles. Activities like hiking in the mountains or cycling for hours on a trail use slow twitch fibers that contract thousands of times in a matter of hours.
The larger, fast twitch fibers produce quick, powerful burst of strength or speed. These fibers use glycogen, stored in the muscle, as their primary source of fuel. Because of the limited fuel supply, fast twitch fibers fatigue very quickly (in less than four minutes). Type IIb fibers are more explosive and fatigue quicker than Type IIa fibers. Track and field events, like the 100 meter sprint or high jump, use fast twitch fibers that contract hundreds of times in a matter of seconds.
Regardless of type, muscle fibers produce the same amount of force in a single contraction. The difference between slow twitch and fast twitch fibers is how quickly they contract and how long they can last.
Training to Increase Muscular Endurance
Because repetitive muscular work is a function of our daily lives, everyone can benefit from a muscular endurance training program. The activities included in a muscular endurance training program are functional and beneficial to a better quality of life. Weight training programs that include moderate loads and a high volume of work have been proven to effectively improve muscular endurance. Guidelines for developing an effective muscle endurance workout include:
- Loads: 50 – 65% of 1RM
- Reps: 15 – 20 repetitions
- Sets: 2 – 4 sets
- Rest: 1 – 2 minutes (in between multiple sets)
- Speed: Slow to moderate
- Frequency: 2 – 4 times/week
Final Thoughts …
Regardless of whether you are a marathon runner, football player or someone who just likes “watching” sports muscular endurance is essential to a good quality of life. Muscular endurance is the foundation for all weight training programs (including more advanced programs for muscle growth, strength and power). With good muscular endurance we can be more effective in our day to day lives and beyond!