When I was in college I worked at the student recreation center, which had a state-of-the-art weight-room. I started working as a cardiovascular and resistance-training specialist (which sounds more prestigious than it actually was). Eventually, I became a personal trainer and quickly began to notice a detrimental pattern. The average “trainee” would do a set of curls (in the squat rack), bench press or crunches with no regard for technique, rest for 5-10 minutes talking with his friends or texting and then repeat another set. Some of these guys would be in the gym for 2-3 hours! As the saying goes, if you’re making friends in the weight-room you’re not making progress.
There’s one training variable that, while not as interesting as sets, reps and tempo, is one of the most important to understand: rest intervals. The amount of rest taken between sets affects the degree and type of energy system and the intensity (% of 1 rep max in a given lift) of the training load.
There is an inverse relationship between reps and rest, therefore the more reps performed per set the shorter the rest period and the fewer reps performed per set the longer the rest period. The relatively lighter loads used when performing multiple reps are more taxing on the muscular system, which recovers faster between sets than when using low reps. The heavier loads used when training for strength taxes the Central Nervous System more, which takes longer to recover between sets than when using high reps.
The body has three primary energy systems: phosphagen system (adenosine tri-phosphate - phospho-creatine), glycolytic and oxidative phosphorylation. The phosphagen and glycolytic systems are anaerobic, which means they do not require oxygen for the production of energy. However, oxidative phosphorylation is aerobic, which means this system does require oxygen for energy production. All of these systems are active concurrently, but the intensity and duration of the activity determines which of the systems is the primary source of energy. The desired training effect must first be considered when deciding how to program rest intervals.
Phosphagen System
The phosphagen and glycolysis systems are of primary importance for football. The phosphagen system provides energy for maximal and super-maximal activities that last up to 20 seconds. Developing this energy system is extremely important for continuous maximal effort, such as a lineman coming off the line. As covered in the previous article we know that this 20-second time frame also corresponds to the optimal length of time for muscles to be loaded when training to increase strength levels.
Much has been written about rest intervals and strength training in physiology journals. The general concept is that when training for strength the work to rest ratio should be 1:5, which means how ever long it took to complete the set it would take 5 times as long to recover. While it is true that the energy stores may have recovered with a work to rest ratio of 1:5, the Central Nervous System has not fully recovered, which means the nervous system is incapable of activating the powerful Type IIx muscle fibers and if these fibers are not stimulated they will not grow stronger.
In his book “The Poliquin Principles” strength coach Charles Poliquin writes about legendary speed coach Charlie Francis using a work to rest ratio of 1:20-30 with his athletes. This longer rest interval ensures that the energy stores are completely restored and the Central Nervous System is once again capable of activating the Type IIx fibers.
For example, take an athlete who is training with 90% of their 1 rep max in the full squat for 2 reps taking 5 seconds to lower the weight, no pause at the bottom and 1 second to raise the weight. The athlete is spending 12 seconds of time under tension and when the 1:20-30 work to rest ratio is applied means this athlete will need between 4-6 minutes of rest between sets, or complete recovery, in order to handle that load for subsequent sets. When using heavy loads to increase strength levels using a work to rest ratio of 1:20-30 is more effective at improving strength levels than a 1:5 ratio.
Glycolytic System
The phosphagen system begins to diminish after about 10 seconds and the glycolytic system then becomes the primary energy system. The glycolytic system continues to be the primary source of energy for activities lasting up to two minutes. This system breaks down stored muscle and liver glycogen (i.e. glucose), the stored form of sugar in the body. Using shorter rest intervals, as compared to training for strength, trains the glycolytic system to become more efficient at processing pyruvate and lactate: the byproducts of glucose being used as a fuel source.
There is a favorable hormonal response when using short rest intervals and multiple reps per set to increase muscular size. Research has shown that when the number of reps per set is between 8-12 and the work to rest ratio is 1:1-2 there is an increase in the release of growth hormone. For example, if an athlete is training to increase muscular size and is performing incline dumbbell presses for 12 reps taking 3 seconds to lower the weight, pauses for 1 second at the bottom position and then takes 1 second to raise the weight. The time under tension for this set is 60 seconds, which means this athlete should take 1-2 minutes of rest between sets.
If the athlete is performing only incline presses 2 minutes of rest is sufficient. However, if they are pairing antagonistic muscle groups a rest interval of only 1 minute is ideal. Pairing antagonistic muscle groups means the athlete would perform a set for a specific muscle group, rest the allotted time then perform a set for the opposing muscle group. In this example the athlete could perform a set of incline dumbbell presses for the prescribed number of reps at the appropriate tempo, rest 1 minute, then perform a set of chin-ups. The athlete would then rest another minute before returning to the incline dumbbell press and repeat this order until all of the prescribed sets are complete and moving on to the next exercise or grouping of exercises.
When training to increase muscular size pairing antagonistic muscle groups is an extremely effective and efficient way to train because it allows for a greater volume of training in a relatively short amount of time. Again, this method is ideal for increasing muscular size because of the hormonal response. An added benefit of this training method is that it also indirectly improves the conditioning level of the athlete because it effectively trains the body to become more efficient at processing the by products of glucose being used as an energy source: pyruvate and lactate.
Using multiple sets of high reps and short rest intervals is a much better method of training athletes involved in strength and power sports than aerobic activity, or “cardio”. Research has shown that an aerobic base is not a factor for athletes involved in these sports and introducing aerobic activity to these athletes corresponds to a drop in strength levels.
In conclusion, the rest interval should be a function of the overall training goal. While the science of rest intervals is not as exciting as other training variables, such as reps, sets and tempo, it is equally as important. Understanding the logic behind when and how to program rest intervals is important for maximizing strength development, muscular size and conditioning. Program appropriate rest intervals to the phases of a strength-training program and start making gains in the weight-room not friends.
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Dynamic Athletics provides one-on-one and small group strength training, consultations on program design, weight-room design, nutritional and supplement. Contact me at cdellasega@darisports.com.
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