What are "local" and "global" muscles?

This blog post is in response to a instagram post made by one of the board members of the Pilates Method Alliance claiming that so called local muscles need to be developed before we can have efficient global muscles. 

There’s been a lot of talk about “local” muscles and “global” muscles and the benefits or detriments of working one over the other. But, what exactly are local muscles and global muscles? How do we know which is which? Do we need to train a specific way to target local muscles over global muscles and is training one over the other better? Let’s dig in!

Defining local vs global can be difficult, in part because there is no consistent definition. Bergmark categorized muscles that stabilize the spine as either local or global. The transversus abdominis (TA) and multifidi are local muscles, whereas the erector spinae, quadratus lumborum, obliques, and rectus abdominis are global muscles. (PMID: 24427424) Lee defined local vs global where global muscles create power and large movements, while the local muscles provide stability by connecting the pelvis and ribcage to the spinal fascia. (PMID: 34886530) and others use the terms interchangeably with stabilizers (local muscles) and mobilizers (global muscles) (Gibbons, Comfort, 2011) assigning muscles like the pelvic floor and rotator cuff as stabilizers and the deltoid and glut max as mobilizers. 

Some researchers further define local vs global as primarily due to fiber type composition where local muscles are composed of type 1 more fatigue resistant fibers and global muscles are composed of type II or more power producing fibers. 

With various definitions of local vs global it’s difficult to come to any conclusions about those muscles when we aren’t starting from the same understanding of what exactly we're talking about. Furthermore, our rotator cuff, rectus abdominis, deltoid, and transverse abdominis are composed of BOTH type I and type II fibers ( PMID: 18978449, PMID: 161688) and that both types respond to loading and task more than occupy a specific role of stability, mobility, power, or postural control. Additionally, there is a growing body of evidence to suggest that training can shift fiber type over time (PMID: 21912291).  

Personal opinion incoming:

So do we need to do specific exercise protocols for local muscles and specific exercise protocols for global muscles? Instead of framing it like this we can frame it as low load high rep exercises will utilize muscles with more type 1 fibers, which are better at doing endurance-based activities and high load/high velocity low rep exercises will utilize more type II fibers, which are better at doing higher load explosive activities. Recruitment is task dependent. And when we have muscle with both fiber types we can assume that they participate in BOTH endurance and explosive activities, not just one or the other.

So, again, do we need to do specific exercise protocols for local and global muscles and, furthermore, do we need to prioritize local over global or global over local? Ideally, we should be doing both low load high rep and high load low rep exercises because both are important. We should go long and slow sometimes, and hard and fast sometimes, and slow and heavy sometimes. It is unlikely that one exercise protocol is going to hit all of those. As in, if you only do Pilates you are unlikely to get high load low rep and hard and fast stimuli. Pilates is really good at low load high rep and longer and slower. As Pilates professionals we do a really good job of helping people with type I fiber recruitment. But if all we're doing is Pilates we are leaving a lot on the table.

Similarly, there is no need to develop type I fibers before we have the green light to develop type II fibers. In other words, we don't need to have strong "local" muscles to have efficient "global" muscles. That would be like saying you need to have a perfect unweighted front squat before you could do a weighted front squat (have you ever tried to do a front squat with a dowel instead of a barbell or dumbells? it's ugly). Sometimes our body organizes better in response to load. Giving someone unfounded parameters around what type of exercise they can do based on unfounded claims is essentially keeping them from achieving their full potential and gatekeeping health, which is literally the opposite of what exercise professionals are supposed to do. 

So encourage people to progressively load into low rep high load short duration, high rep low load long duration, explosive power... do Pilates, weight training, slow jogging, hill sprints, handstands, pull ups, push ups, deadlifts, lunges... It's not our job to take movement options away from people. Instead, we should help them find movement solutions.