Rest Intervals 101

When you are about to hit the gym, you generally have a plan of what you’re going to do: “What muscle group am I working? Will I try to hit a new max? How many sets will I do?” But the question of “how long should I rest for?” often is overlooked. Resting between sets is important because the chemical processes in your body that happen while putting in effort could cause fatigue. 
 
The best amount of time to rest between sets varies based on what goal you are training for. You could be missing out on strength gains if you are working too hard, or you could be missing out on muscle growth if you take too long of a rest. 
 
Intervals for Training for Strength or Power
 
To get stronger faster, an ideal rest period between sets is 3-5 minutes. Why? It takes your body around 3 minutes to replenish phosphagen stores. Your body needs to get energy to consume during training, and that comes from the Adenosine Triphosphate Phosphocreatine system (ATP-PC). Your body only has a small reserve of phosphagen, lasting about 15 seconds. 
 
Hence, by letting your ATP-PC system rest and recharge for around 3-5 minutes, you will be able to lift more weight, resulting in faster gains in strength. Any longer than 5 minutes though, your body will cool down considerably, which could increase the chance of an injury. 
 
Intervals for Training Muscle Growth
 
Now, when focusing your workouts with the goal of building mass and getting bigger quickly, the ideal rest period is 1-2 minutes between sets. While hypertrophy training still uses your ATP-PC system, your glycolytic system (which gets most of its energy from consumed carbs) and aerobic metabolism are used as well. However, the glycolytic system takes a load off the ATP-PC system and your body does not need to rest as long as it does when you are training for strength. 
 
Obviously one of the factors in how much muscles grow is the amount of anabolics in your body, or that your body produces. A shorter rest period of 1-2 minutes can cause a greater release of these hormones as opposed to a longer rest of 3-5 minutes. Another way short rest periods can help build muscle are the increased lactate production and blood flow. Increased blood flow does help protein reach your targeted muscles quicker.
 
Intervals for Endurance Training
 
While doing endurance training (light/moderate weight with higher reps), the ideal range for a rest period between sets is 45 seconds to 2 minutes. Endurance training uses a lot of its energy from aerobic metabolism or breaking down carbs and fats in the presence of oxygen. 
 
The main goal for endurance training is to make your muscles more resistant to fatigue. Considering that lactic acid build up is a major cause of fatigue, it should be noted that lifting weights regularly in the 15-20 rep range can make your body better at clearing lactic acid from the targeted muscles. It does this by boosting your body’s vascular and hormonal systems.
 
A guide to better work out the ideal range for you is to follow a 1:1 or 1:2 work/rest interval. Doing so will increase your body’s lactate threshold. Typically, a set of 15-20 reps should take you around 45 seconds to 1 minute to finish, therefore the rest period works out to be between 45 seconds and 2 minutes. 
 
Final Thoughts
 
Different guidelines apply to other forms of exercise like circuit training or complexes, but a general rule of thumb for your training goals (strength, muscle, or endurance) is that the heavier the weight you are lifting, the longer your rest period should be (generally). Other factors such as technical nature of the lift, your training progress, fatigue levels, and more can affect how much rest you may need during any type of workout. Rest periods or intervals should not be overlooked. Your rest periods need to reflect your training goals.