Day: September 10, 2012

Metabolic Energy Systems 101

At certain points during exercise your body uses the three energy systems (that we know about as of now…there may be more energy systems that we don’t yet understand) APT-Phosphocreatine, Anaerobic Glycolysis and Aerobic. Your body converts carbohydrates, and in fasting situations fatty acids and amino acids, into glucose. Glucose will then be broken down through Glycolysis to make ATP (energy). This can be done anaerobically (without oxygen) and aerobically (with oxygen). When we are working out at a high enough intensity to cause rapid breathing (above 75% max heart rate) we are working anaerobically and challenging our phosphagen system and glycolysis. When we are working out aerobically (under that 75%) our body can breakdown glucose and perform many other aerobic metabolic processes that keep our body fueled with ATP. Glucose is then taken into the cell and converted into a chemical energy molecule called adenosine triphosphate, or ATP.

Your muscle has a small amount of ATP floating around that it can use but not a lot- only enough to last for about the first three seconds of an exercise. To replenish these levels, the body uses a high-energy phosphate compound called creatine phosphate (you may have heard of the supplement creatine-monohydrate…this is what it is used for) to make more ATP. This cycle keeps adding a phosphate to make ATP once it has been used for energy. The ATP and creatine phosphate together are called the phosphagen system. The phosphagen system can supply energy needs to a working muscle for about 10 seconds before needing to go through this conversion cycle again.

Analysis of the Rest Periods

Perhaps you’ve already asked yourself what the benefit is of a rest period, when to use it and why. It is easy to get confused concerning this topic, but the answer is related to goal and intensity level. Rest periods are an amount of time between sets ranging from 30 seconds to 5 minutes. According to American College of Sports Medicine, ACSM, Resources for the Personal Trainer, 3rd edition, rest periods can be categorized using this scale:

  • Very short rest periods- 1 minute or shorter
  • Short rest periods- 1-2 minutes
  • Moderate rest periods- 2-3 minutes
  • Long rest periods- 3-4 minutes
  • Very long rest periods- 5 minutes or longer

According to research, it takes approximately 2.5 to 3 minutes for complete resynthesis of APT stores and 8 minutes for complete creatine phosphagen repletion after an intense exercise (both translate to anaerobic energy). There is increased use of both glycolytic (aerobic and anaerobic breakdown of glucose as energy) and ATP-CP during high intensity. Glycogen stores and blood glucose will lower in addition during high intensity, which equates to multiple metabolic processes (aerobic and anaerobic) being stressed.

According to National Strength and Conditioning Association, NSCA, The Essentials of Strength Training and Conditioning, 3rd edition, phosphagen concentrations during high-intensity training anaerobic exercise can decrease (50-70%) during the first 5-30 seconds of high-intensity and can be depleted to almost eliminated upon complete exhaustion. On the other hand, to improve the body’s bicarbonate, phosphate, blood and muscle buffering systems, less rest is required. So, which yields greater benefits?

Strength athlete/ power= optimal rest period is 3 to 5 minutes.
A strength athlete will train explosive (fast, powerful movements), low repetition activities of short duration. It is also common to see plyometrics (drills that increase speed, agility and quickness) incorporated into the program. A strength athlete (includes power lifters and athletes involved in sports that require high intensity, short bursts) is usually concerned with performance in relation to maximal power that can be produced. This type of routine focuses on strength and not hypertrophy or endurance. This high intensity style training will increase the heart rate (utilizing and depleting all the anaerobic energy within the set) and will increase the release of testosterone to produce maximal muscular output. The recommended rest period for anaerobic activity should be from 3 to 5 minutes.

Muscle growth/ endurance conditioning= optimal rest period is 30 to 60 seconds.
For increased hypertrophy as well as endurance sport conditioning training, the workout should have a slower tempo, 8- 12 repetition range, and the goal is to achieve close to maximal force output by a muscle over a time period. The typical rest period for this type of programming is between 30 to 60 seconds, or a 1:1 ratio of work to rest. The body buffers the effect of increased lactate in the muscles. This type of training increases production of Human Growth Hormone and thus hypertrophy of the muscle.

Circuit/ superset training= optimal rest period is 30 seconds.
Circuit or superset training is designed to combine the effects of strength and aerobic training, so rest periods are minimal from 30 seconds to a 1:1 ratio, and thus limits max output. This type of training can have multiple benefits (sometimes less measurable in strength, but definitely measurable in aerobic capacity), and can be useful in weight loss and toning. According to research, strength gains are limited to only 30-50% the benefit of strength training.

One study done by NSCA in the Journal of Strength and Conditioning Research, Effects of Different Weight Training Exercise/Rest Intervals on Strength, Power, and High Intensity Exercise Endurance, tested if short rest periods between sets enhances high intensity exercise endurance (HIEE). Their findings concluded that sufficient rest between sets are more likely to lead to greater increase in maximum strength and performance; intensity has great importance in relation to performance (especially concerning maximum strength); and short rest periods have less positive effect on HIEE than incorporating additional sets or repetitions.

So, which routine and rest period is best for you? Many certification bodies recommend a systematic approach to periodization generally consisting of a strength base, followed by power, and then a recovery phase. Each of these should have a different intensity and rest period associated with them. Remember your approach to programming should be focused on stimulation and finding challenge in the activity.

For more information, please contact Amber Walz.