Recovery is commonly overlooked as an important aspect of training. Whether the goal is performance related, aesthetics, weight loss, or overall health; recovery allows the body to adapt in order to improve efficiency in function and performance. Allotting the proper amount of time for muscle recovery between workouts is crucial in preventing overtraining and injury; but what about recovery  _during_ a workout?  Intra-workout recovery, or ‘rest time’ is often neglected as an important part of training. Oftentimes people will socialize or scroll through their phone between sets, without having any true concept of how rest intervals contribute to their goals. Goal specific workouts require different rest intervals; just as they require different sets and repetitions. The following are general guidelines for rest times, according to their goals:[¹](https://www.acsm.org/docs/default-source/publications-files/intro-to-exsci-3_sample-chapter-3.pdf?sfvrsn=2c9320fb_8#:~:text=A%20systems%20approach%20to%20the%20study%20of%20exercise%20science%20allows,and%20chronic%20stimuli%20and%20conditions.) [²](https://www.nsca.com/store/product-detail/INV/9781492501626/9781492501626) [³](https://journals.lww.com/nsca-scj/fulltext/2019/10000/energy_system_development_in_the_weight_room_.7.aspx) * Strength and Power: 3 - 5 minutes * Strength being the lower end of rest time as opposed to power  * Hypertrophy (muscle growth): 30 - 90 seconds * Muscular Endurance: 30 seconds or less * Commonly used for weight loss programs The rest periods above are based on the body’s energy systems used during each workout. While all three systems generally contribute to energy production in a single workout; specific goals, intensity, and duration determine the necessary time interval to recover depleted ATP levels -- a major goal of intra-workout recovery. **Energy Systems** _Phosphagen (ATP - PC) System_  The ATP (adenosine triphosphate) - PC (phosphocreatine) system is the body’s immediate energy system. Immediately available ATP (energy) supplies are used to product movements with a high force and explosive power. Most prevalent in the initiation of a movement, this system produces the most energy for a period of time lasting from 10-15 seconds before total exhaustion. According to  _ACSM_, the phosphagen system provides energy during the initiation of a movement and during high intensity exercise.[¹](https://www.acsm.org/docs/default-source/publications-files/intro-to-exsci-3_sample-chapter-3.pdf?sfvrsn=2c9320fb_8#:~:text=A%20systems%20approach%20to%20the%20study%20of%20exercise%20science%20allows,and%20chronic%20stimuli%20and%20conditions.) When training for strength and power, it is important to allow complete ATP resynthesis; occurring over 3 - 5 minutes of rest. Regardless of the natural reduction in strength and power as you progress through a workout, the idea is to restore immediate ATP levels that the muscles needs to perform at its peak during the following set.  Training for strength and power is crucial for any athlete with a need for quick acceleration and explosive power. Some examples are Olympic lifters, powerlifters, sprinters, gymnasts, and football linemen. Adjusting rest time to support this type of training may help improve the ability to withstand longer durations at this intensity.  _Glycolytic System_  The glycolytic (anaerobic) system provides energy for activity at medium to high intensity lasting anywhere from 10 - 120 seconds. This system breaks down glycogen (stored glucose) in the muscles and liver, or glucose in the blood, to produce ATP for energy. [¹](https://www.acsm.org/docs/default-source/publications-files/intro-to-exsci-3_sample-chapter-3.pdf?sfvrsn=2c9320fb_8#:~:text=A%20systems%20approach%20to%20the%20study%20of%20exercise%20science%20allows,and%20chronic%20stimuli%20and%20conditions.) [²](https://www.nsca.com/store/product-detail/INV/9781492501626/9781492501626) Training a moderate-high intensity, followed by moderate rest, helps stimulate muscle growth. That being said, resistance training in an 8-12 repetition range, at a moderately high intensity, exhausts the glycolytic system. A rest range of 30 - 90 seconds will give the body time to replenish energy levels, trigger adaptation, and stimulate muscle growth.  Combat sports, baseball, soccer, basketball, and skill players in football will heavily rely on this system.  In addition, bodybuilders will focus on this rest interval because they will train for hypertrophy in the optimal 8-12 rep range.  Athletes may want to train this system to improve energy production for this intensity and reduce lactic acid buildup.  _Oxidative System_  The oxidative (aerobic) system provides energy for activities lasting more than 2 minutes. After 2-3 minutes using the ATP - PC and glycolytic systems, the oxidative system will kick in by breaking down carbohydrates, fats, and proteins for energy. Although the slowest, it is the most utilized of all the energy systems. It operates during rest and at low intensities, taking much longer to exhaust. As a result, rest periods remain under 30 seconds for adaptation to increase training time at a sustained intensity. [¹](https://www.acsm.org/docs/default-source/publications-files/intro-to-exsci-3_sample-chapter-3.pdf?sfvrsn=2c9320fb_8#:~:text=A%20systems%20approach%20to%20the%20study%20of%20exercise%20science%20allows,and%20chronic%20stimuli%20and%20conditions.) [²](https://www.nsca.com/store/product-detail/INV/9781492501626/9781492501626) Cardiovascular and muscular endurance training often utilize the aerobic system which need shorter rest times to recover. Athletes training for endurance such as marathon runners, crew, and long distance swimmers are aerobic activities that require rest only as needed; therefore rest periods will also be shorter in any muscular endurance weight training. Aerobic training allows the body to better utilize oxygen and sustain prolonged, higher intensity activity.  **What Does This Mean?** Each energy system is designed to handle levels of intensity for different periods of time. As previously explained, a greater intensity will lead to quicker exhaustion because the energy systems involved can only sustain activity up to 2 minutes. The phosphagen system provides fast, large bursts of energy for a short duration whereas the oxidative system provides a slow, sustained energy for a long duration.   To help further explain this concept, think of a sports car as the phosphagen system and a hybrid, economy car as the oxidative system. If both cars take off down the highway for a predetermined distance, the sports car would take off with the most speed and power. Assuming the two vehicles had the same size gas tank, the slower hybrid car would undoubtedly finish the distance with more gas in the tank due to its higher mpg. While fueling up (restoring ATP levels) for the next round, the hybrid would require less time to fill the tank than for the sports car. Therefore, the hybrid is built for energy efficiency and endurance; whereas the sports car is built for speed, power, and performance.    Ultimately, the goal of intra workout recovery is to restore/sustain energy (ATP) levels for peak performance. Rest, dependent on training intent, will aid in adaptation and progression for the future.[⁴](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4424454/) [⁵](https://pubmed.ncbi.nlm.nih.gov/28753624/) Shorter rest intervals help elevate heart rate, endurance, calorie burn, and weight loss. On the other hand, longer intervals typically aid in muscle growth and optimal performance. So before you get caught up on your phone or start conversing between sets, don’t forget to keep a close eye on the clock so you know when it's time to get back to work!