This split would deliver an optimal training frequency for most people:

• Day 1: Upper body and calves
• Day 2: Legs
• Day 3: Back, biceps, rear and lateral delts
• Day 4: Chest, triceps, calves, rear and lateral delts
• Day 5: Legs and biceps
• Day 6: Back, biceps, triceps, rear and lateral delts
• Day 7: Off

Note: On day 1, train back, chest, shoulders, biceps, and triceps. Leg days include the quads, hamstrings, glutes, and calves.

Research indicates that anything from 2-4 times per week is best when training for muscle growth. Identifying where on this range each muscle sits will allow you to unlock your growth potential by training each muscle at the perfect frequency.

Different muscles respond to training differently and have their own recovery times, or SRA curves. The length of the SRA curve for hypertrophy varies based on several factors like the size of the muscle, its structure, function, fiber type ratio, the disruption caused when training it, your training age, and your strength levels.

Despite all these differences, the duration of the curve can be narrowed down to a matter of days. For bodybuilding-style training, it's generally around 24-72 hours. But there's still a significant difference between muscle groups.

For example, a tough quad workout causes more disruption and fatigue than a tough biceps workout, so it requires a longer recovery period. Using this logic, it makes sense to have a higher training frequency for biceps than quads.

Almost everyone could train the rear delts 4 times per week without any adverse effects on recovery. In reality, you might even be able to train them daily. But you certainly can't train hamstrings that way.

When assessing your own overall optimal training frequency, you should consider the following factors:

• Your training age/experience
• Your strength levels
• Your size/level of muscle mass

As you get more experience and grow bigger and stronger, the frequency with which you can train a muscle might actually diminish. The more muscle on your frame and the stronger you are, the more disruption you cause when you train. Therefore, you need heavier weights and a greater training volume to cause overload. This means you dig a deeper recovery ditch during each workout and recovery takes longer. Other factors include:

Different muscle groups have different functional characteristics and tend to have varying fiber-type ratios. The soleus (part of the calf) for example, is a slow-twitch (type I) dominant muscle while the triceps tend to be fast-twitch dominant (type II).

Slow-twitch muscle fibers recover more quickly, both within a workout and from session to session, than their fast-twitch counterparts. Consequently, training muscles that are predominantly slow twitch more frequently makes sense.

In general, the classification of muscle fiber-type ratios are:

• Hamstrings: Mixed, 44-54% type I
• Quads: Mixed, 44-64% type I
• Glutes: Mixed with a tendency towards slow twitch, 52-60% type I
• Chest: Fast twitch, approximately 60% type II
• Calves: Slow. Gastrocnemius roughly 44-76% type I. Soleus in the range of 70-96% type I.
• Spinal Erectors: Slow, 63-73% type I
• Traps: Mixed
• Shoulders: Mixed fiber distribution with a slight type I dominance
• Triceps: Type II
• Lats: Greater proportion of type II
• Biceps: Tendency towards fast twitch dominant, approximately 40% type I

Individual differences are also a factor. Usain Bolt almost certainly has a higher proportion of fast-twitch fibers than most people. Distance runner Mo Farah, meanwhile, likely has a greater slow-twitch dominance.

But it's quite possible that muscles that are generally considered fast or slow might be the opposite for you. If this is the case, you'll probably know quickly. For example, a muscle is likely fast-twitch dominant if you're explosively strong when training it, but find your ability to perform higher-rep sets with it is poor. These fast-twitch muscles will also take longer to recover than other muscles.

If you have a higher predominance of slower-twitch muscle fibers, you can most likely tolerate and benefit from higher frequency training. On the other hand, if you have above average numbers of fast-twitch fibers, then you'll probably benefit from lower frequencies of training.

Training larger muscles causes more homeostatic disruption, and bigger muscles take longer to recover. Bigger muscles can produce more force and handle heavier loads. Their larger volume also dictates that the quantity of tissue to be repaired and remodelled is greater. Naturally, this takes longer for bigger muscles. After all, it would take longer to knock down and rebuild a skyscraper than a townhouse. By extension, smaller muscles recover faster, so they can be trained more frequently than larger muscles.

But size isn't the only consideration. A muscle's architecture is another key factor: the structure and arrangement of fibers across a muscle's contractile range. Depending on the pattern of these arrangements, muscles display varying force outputs and varying propensity to stretch under load. This needs to be considered when planning training frequency.

For example, most people can progress well using a high frequency of upper body pulling work. The chest muscles, however, which are much smaller than muscles of the back, rarely benefit from a training frequency greater than twice a week because of their fiber type and architecture.

While we can make general recommendations based on specific muscle characteristics, the exercises you choose also influence training frequency. Some cause greater systemic fatigue while others create more local fatigue.

In the end, there's a trade-off between choosing the most effective exercises (those which cause the greatest stimulus and adaptation) and the frequency with which a muscle can be trained using these movements. In most cases, choose the "best" exercises and train them at an appropriate frequency, as opposed to chasing higher frequencies with "inferior" exercises.

• Exercises that place a significant stretch on a muscle cause more damage and take longer to recover from. Good mornings, for example, create a far greater stretch on the hamstrings than leg curls. This causes higher levels of muscle damage and somewhat extends the muscle's SRA curve. So, if you're trying to train the hamstrings frequently, biasing your training towards leg curls with the conservative use of exercise like good mornings and Romanian deadlifts would be wise.
• Range of motion is also a consideration when it comes to exercise specific SRA curves. Movements with a greater ROM cause greater systemic fatigue because they have a higher workload. As such, deficit deadlifts create more fatigue than pulling from blocks and cambered bench presses require more work per rep than board presses.
• Barbell movements tend to be harder to recover from than dumbbell movements, and dumbbell movements harder than cables or fixed machines. Isolation exercises also tend to be easier to recover from than multi-joint movements. So, at one end of the spectrum for quads you have high-bar squats and at the other end you have leg extensions.
• If you're used to just blasting a muscle once per week, don't jump in at the deep end. Gradually increase your training frequency over several months. As you do, meticulously track your progress. Identify patterns and see how different frequencies affect your progress. In time, you'll begin to identify your optimal training frequency for each body part. Once you arrive at your recovery rates, you're then in a position to structure your program around them.