By Erick Avila
An inter-set rest period is the recovery time between exercise sets. These rest periods can be active rest periods where you maintain an elevated heart rate by doing some form of physical activity (like jogging in place) between your main exercise set, or passive rest periods where you aren’t physical active while recovering between sets.
One of the most common questions in fitness is, “How much time should I rest between sets?” The answer to this will vary depending on an individual’s fitness level, the type of workout, and personal goals.
In “Foundations of Fitness Programming” by the National Strength & Conditioning Association, the general guidelines for rest periods are:
<= 30 seconds for muscular endurance 
30-90 seconds for hypertrophy (muscle growth) 
2 – 5 minutes for strength or power training 
The basis for these rest period recommendations is rooted in how the body utilizes energy to perform specific tasks. The body uses three main energy systems to fuel our activities, however, the reliance on the systems will vary based on the intensity and duration of the activity. Ultimately, all three of these energy systems work to supply our muscles with ATP (adenine triphosphate), the energy currency of cells.
Breaking Down the Basics: The 3 Energy Systems
ATP-PCr System: Fast Acting Energy
The ATP-PCr (adenine triphosphate – phosphocreatine) system fuels strength and power activities lasting a few seconds like a one rep max lift or a 40-yard dash. This system utilizes ATP to power these high-intensity activities. The ATP that's used to fuel these activities releases energy and gets converted to ADP (adenine diphosphate). Research shows that partial resynthesis of this system takes about 1-2 minutes, but complete resynthesis may take as long as 5-15 minutes. [2,3]
Glycolytic System: Medium Duration Energy
The glycolytic system is the energy system that’s primarily used for activities lasting 30 seconds to 3 minutes, like a high rep drop set or a 400-meter dash. The glycolytic system utilizes glucose from muscle glycogen breakdown and blood glucose as a fast-acting fuel source to generate ATP. This system can be utilized for both aerobic and anaerobic exercises.
The majority of glycogen in our body is stored in our muscles (about 350-700 grams) and our liver (about 100 grams). Although these figures will vary depending on factors like lean body mass and diet. [4,5,6]
Exercise that exceeds our maximal oxygen uptake level (VO2 max) will utilize carbohydrates as the primary fuel source.
Because of this many athletes that do high-intensity exercises will often consume carbohydrates before and after tough workouts to replenish their glycogen stores. Trained athletes take about 2-3 minutes of recovery time for maximum ATP resynthesis following a glycolytically demanding activity.
Oxidative System: Slow and Steady Energy
The oxidative system is the main energy system used for activities ranging from a few minutes to several hours, like an obstacle course race or a triathlon. The oxidative system uses fatty acids from muscles and adipose tissue to generate ATP. The body can generate a significant amount of ATP from fatty acids, but the rate of production is significantly slower than the glycolytic and ATP-PCr systems. Aside from being used during low intensity exercise, the oxidative system is also the energy system used when we’re resting.
Interval training is an exercise method characterized by its stop-and-go nature. Interval training consists of periods of higher intensity movements separated by periods of rest. This style of training normally utilizes aerobic modalities like a treadmill, bike or rowing machine. Although it can also be done with resistance training movements as well.
Some forms of interval training include
HIIT (high intensity interval training) defined as being 70-90% of one’s VO2 Max or 86-95% of one’s peak heart rate.
SIT (sprint interval training) may be as high as 350% of one’s VO2 Max. 
Fartlek training also known as speed play where intervals are mixed into continuous endurance training.
The rest to work ratio for interval training will vary depending on individual levels of physical fitness and the desired intensity of your intervals. A 1:1 work to rest ratio is common for HIIT while SIT training may use work to rest ratios as high as 1:10. In general, the higher the relative intensity, the longer you’ll need to rest.
A sample HIIT circuit workout with a 1:1 work to rest ratio could consist of
Work: 30 seconds
Rest Between Exercises: 30 seconds
Rest Between Circuits: 3 minutes
Medicine Ball Slam
With a circuit workout like this, your ATP-CPr, glycolytic and oxidative systems will all be used.
Train Smarter by Choosing the Right Rest Times
In a 2012 meta-analysis on rest intervals for strength training, the researchers concluded that for individuals training between 50-90% of their 1 rep max, 3-5 minutes of rest between sets allowed for greater increases in absolute strength, power, and reps completed 
In a 2017 systematic review evaluating the impact of rest intervals for muscular strength in trained and untrained individuals, the researchers noted a difference among the groups. While it was possible to make strength gains with rest intervals of 60 seconds or less, greater gains were seen in trained individuals resting for more than 2 minutes. The researchers also noted that for untrained individuals 1-2 minutes of rest was sufficient for making strength gains.
Turbocharge Your Fuel Tank
When it comes to how long should you rest between sets, the answer is it depends on your workout style, goals, and experience levels. Having a higher VO2 max will allow you to recover faster from high intensity power training. One strategy that some athletes have utilized to support muscle recovery and endurance is supplementing with XTEND Elite®. XTEND® Elite features PeakO2® a mushroom blend that has been clinically studied to increase VO2 max and time to exhaustion. It also features CarnoSyn® Beta-Alanine for improved muscular endurance and NO3-T® Citrulline Nitrate for increased blood flow. [13,14]
Turbocharge your fuel tank by adding a scoop of XTEND® Elite to your daily routine, so you can get the most out of every workout.