Whether muscles grow more on rest days or training days is a common debate among fitness enthusiasts and athletes. The answer depends on understanding the muscle building and recovery process. When we strength train, we create small tears in the muscle fibers. The body then repairs these tears by fusing the fibers together, making them larger and stronger. This is how muscles grow. However, this repair process requires adequate rest between training sessions. So while the actual muscle growth may occur more during rest days, both training and rest are essential for hypertrophy (muscle growth).
Do muscles actively grow during rest days?
Yes, muscles undergo the most active repair and growth during rest days. Here’s why:
- Lifting weights causes microscopic tears in the muscle fibers. The body repairs these tears by fusing old and new muscle proteins together, resulting in larger and stronger fibers.
- This repair process is energetically demanding and requires various cellular and hormonal mechanisms.
- During training, the priority is performing the exercise with proper form and intensity. There is less energy available for repair.
- On rest days, the body directs its resources specifically towards repairing and rebuilding the muscle tissue.
- Rest days allow levels of muscle protein synthesis (MPS) to exceed muscle protein breakdown (MPB). This stimulates growth.
- Adequate rest, nutrition and sleep on off days optimize the environment for muscle protein synthesis.
Therefore, the actual muscle fiber growth occurs more rapidly during rest days as the body directs its energy towards recovery. However, exercise provides the stimulus for this growth process.
Why are rest days important for muscle growth?
Rest days are crucial for muscle hypertrophy for several reasons:
Prevent overtraining
Overtraining can occur when the body is not given adequate time to recover between intensive exercise sessions. This leads to impaired muscle repair and growth. Rest days help prevent overtraining symptoms like fatigue, decreased performance, insomnia, and muscle loss.
Allow complete muscle recovery
Muscle fibers need 24-48 hours to fully recover after strength training. Insufficient rest between sessions can cause residual fatigue and suboptimal muscle repair and growth.
Restore energy stores
Weight training depletes muscle glycogen stores needed for energy production. Rest days allow the body to replenish these glycogen stores so muscles have ample energy for the next bout of exercise.
Increase anabolic hormones
Growth hormone and testosterone are anabolic hormones that stimulate protein synthesis and muscle growth. Rest days allow these hormones to return to baseline levels for maximal adaptation.
Enhance muscle repair mechanisms
Satellite cells help fuse muscle fibers for repair and growth. Rest enhances satellite cell activity and allows inflammation from training to subside so they can do their work.
Rate of muscle protein synthesis over time
Muscle protein synthesis (MPS) remains elevated for 24-48 hours after strength training before returning to baseline levels. Here is an overview of the MPS response:
- MPS increases rapidly after training, peaking around 24 hours.
- It remains elevated above baseline for up to 48 hours post-workout.
- By 72 hours, MPS returns to normal as muscles have fully recovered.
- Muscle protein breakdown follows the opposite pattern, lowering during rest days.
This emphasizes the importance of the 24-48 hour rest window for maximizing muscle repair and growth after training.
Other recovery processes enhanced during rest
In addition to muscle protein synthesis, other processes critical to recovery and growth occur during rest:
Glycogen resynthesis
Muscles replenish their glycogen energy stores on rest days to power the next workout.
Removal of metabolic waste
Waste products like lactate are transported out of the muscles to reduce soreness and fatigue.
Activation of satellite cells
These stem cells proliferate during rest to facilitate muscle repair, regeneration, and growth.
Reduction of inflammation
Muscle inflammation from training subsides so repair processes can begin.
Muscle capillarization
More capillaries form during rest to deliver oxygen and nutrients critical for recovery.
How much rest do muscles need to grow?
The optimum rest period depends on your training intensity and volume:
- For heavy strength training, take 48-72 hours of rest between working the same muscle groups.
- Muscles need 24-48 hours of recovery after moderate intensity training.
- With lighter training, muscles may only require 24 hours of rest between sessions.
- Allow longer recovery up to 72 hours for large muscle groups like legs.
- Sufficient sleep (7-9 hours) enhances recovery during rest days.
Build in 1-2 full rest days each week where you don’t train that muscle at all. This allows sufficient time for complete muscle repair and growth.
Sample strength training split with rest days
Here is an example 5 day training split that provides sufficient rest for each muscle group:
| Day 1 | Chest |
|---|---|
| Day 2 | Legs |
| Day 3 | Rest |
| Day 4 | Back |
| Day 5 | Shoulders |
| Day 6 | Arms |
| Day 7 | Rest |
Nutrition and recovery on rest days
Nutrition remains important on rest days to provide the raw materials for repair and growth:
- Consume sufficient protein – 0.4-0.5g per lb of bodyweight, spread over 3-4 meals.
- Fill the remaining calories with carbs and healthy fats for energy needs.
- Take a slow-digesting casein protein shake before bed to sustain muscle protein synthesis overnight.
- Consider carbohydrate refeeding if training hard multiple days in a row.
- Increase calories if in a calorie deficit – muscles need energy to recover.
- Stay well hydrated – water supports many cellular processes.
Proper nutrition enhances the muscle building processes during rest days for optimal gains.
Other rest day recovery tips
Here are some other ways to maximize muscle recovery on off days:
- Get a light active recovery session like walking or cycling to increase blood flow.
- Use self-myofascial release tools like a foam roller to relieve muscle tightness.
- Stick to light mobility work to assist muscle repair without further fatigue.
- Take anti-inflammatory supplements like fish oil and turmeric.
- Get a sports massage if budget allows – aids recovery and relaxation.
- Use topical pain relievers like CBD cream or light icing to soothe sore muscles.
Balance proper rest with some active recovery techniques for optimal muscle repair and growth.
Conclusion
While the stimulus for muscle growth comes from strength training, the actual hypertrophic adaptations take place during rest and recovery between workouts. Rest days allow muscle protein synthesis to exceed breakdown, enabling the body to repair and rebuild muscle fibers bigger and stronger. Allow 24-48 hours between training sessions for the same muscle groups. Nutrition, sleep, and some light active recovery enhance the muscle growth processes on rest days. Remember to balance your training with adequate rest for maximal gains.