As a follow-up to yesterday's "series premier," I wanted to use today's post to discuss another topic that rarely gets sufficient attention in the typical exercise science textbook: synergists and antagonists.
The typical explanation of the relationship of the two is that they're on opposite sides of the joint and perform opposite actions. As an example, the hamstrings flex the knee, and quadriceps extend the knee. Simple enough, right? Not so much.
Muscles can be synergists and antagonists at the same time.
Let's just look at the hip extensors to explain this point. Your primary hip extensors are the hamstrings, gluteus maximus, and adductor magnus (there are more, but we're keeping this discussion simple). They all work together to extend the hip each time you squat, lunge, deadlift, sprint, push the sled, or bust a move on the dance floor. That said, the hip can do a lot of things as it extends.
If we use more gluteus maximus and biceps femoris, it externally rotates and abducts a bit as we extend. If we use more adductor magnus, semitendinosis, and semimembranosus, it internally rotates and adducts.
Taking it a step further, as the hamstrings extend the hip, they have little control over the femoral head, so it tends to glide anteriorly in the acetabulum (hip socket) in a hamstrings-dominant hip extension pattern. The glutes have more direct control over the femoral head and can posteriorly pull the head of the femur to avoid anterior hip irritation (usually the capsule). Shirley Sahrmann did a great job of outlining femoral anterior glide syndrome in her landmark book, Diagnosis and Treatment of Movement Impairment Syndromes.
Herein exists the issue: typical discussions of synergists and antagonists focus on things things:
1. Single planes of motion (sagittal, frontal, transverse), but not the interaction of multiple planes
2. Osteokinematics (gross movement of bones at joints: flexion/extension, abduction/adduction, internal/external rotation), rather than arthrokinematics (smaller movements at joint surfaces: rolling, gliding, spinning)
3. Active restraints (muscles, tendons), but not passive restraints (ligaments, bones, labra, intervertebral discs) that may be synergists to them in creating stability
As another example, think about stabilization at the glenohumeral (shoulder's ball and socket) joint. There are a wide range of movements taking place, yet these movements must be controlled arthrokinematically in a very precise range via a complex system of checks and balances at the joint. If the active restraints (primarily the rotator cuff) don't do their job, one could wind up with stretched/torn ligaments, a torn labrum, or bony defects. In other words, it isn't a stretch (no pun intended) to say that muscles can be synergists to ligaments. Put that in your osteokinematic pipe and smoke it!
This is really a topic that deserves far more than a 500-word post; it could be an entire college curriculum in itself! And, the more you can understand it, the better you'll be able to help your clients and athletes. A great resource to get the ball rolling in this regard is Building the Efficient Athlete, a two-day seminar Mike Robertson and I filmed with functional anatomy heavily in mind.
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The other day, I got an email from another fitness professional saying that he really liked my Maximum Strengthtraining program, but that he'd have left out the reverse crunches if it was his strength training program because he "doesn't use any lumbar flexion work" in his programming anymore.
Given that the book was published in 2008, I'd gather that he is under the assumption that I've jumped on board the anti-flexion bandwagon that's been piling up members in droves over the past 3-4 years. That perception certainly has backing. Afterall, if you want to herniate a disc, go through repeated flexion and extension at end range. If you want to see a population of folks with disc herniations, just look at people who sit in flexion all day; it's a slam dunk.
And, you certainly don't want to go into lumbar flexion with compressive loading. As far back as 1985, Cappozzo et al. demonstrated that compressive loading on the spine during squatting increased with lumbar flexion.
These points in mind, I'm a firm believer that you should avoid:
a) end-range lumbar flexion
b) lumbar flexion exercises in those who already spend their entire lives in flexion
c) lumbar flexion under load
It seems pretty cut and dry, right? Don't move your lumbar spine and you'll be fine, right? Tell that to someone who lives in lumbar hyperextension and anterior pelvic tilt. Let me make that clearer:
Flexion from an extended position to "neutral" is different than flexion from "neutral" to end-range lumbar flexion.
In the former example, we're just taking someone from 20 yards behind the starting line up to the actual starting line. In the latter example, we're taking someone from the starting line, through the finish line, and then violently through the line of people at the snack shack 50 yards past the finish line as nachos and Italian ice fly everywhere and the spectators scurry for cover. You get a gold star if you take out the band, too.
If you're someone who trains predominantly middle-aged to older adult clients, by all means, nix flexion exercises. However, I deal with loads of athletes - most of whom live in lumbar extension and anterior pelvic tilt.
Now, I'll never be a guy who has guys doing sit-ups or crunches, as they can shorten the rectus abdominus, thereby pulling the rib cage down when we're working hard to improve thoracic extension and rotation. Additionally, most athletes absolutely crank on the neck with these - and that leads to a host of other problems.
Enter the reverse crunch, which selectively targets the external obliques over the rectus abdominus. As Shirley Sahrmann wrote in Diagnosis and Treatment of Movement Impairment Syndromes, "The origin of this muscle from the rib cage and its insertion into the pelvis are consistent with the most effective action of this muscle, that is, the posterior tilt of the pelvis."
We utilize the reverse crunch as part of a comprehensive anterior core strengthening program that also includes progresses from prone bridging variations to rollout variations and TRX anterior core work (and, of course, anti-rotation exercises to improve rotary stability). And, I can say without hesitate that this addition was of tremendous value to an approach that got cranky baseball hips and spine healthier faster than ever before at Cressey Performance.
In summary, remember that flexion isn't the devil in a population that lives in extension. Contraindicate the person, not the exercise.