In order to fully understand muscle imbalances, let’s first look at normal muscle function. There are three types of muscles in the body: smooth, cardiac, and skeletal. We, of course, are investigating skeletal muscles – or the muscles that move our bodies through the swim, bike, run movement patterns. Normal muscle activation is a combination of contraction and relaxation of muscle fibers. The technical terms are called facilitation (contraction) and inhibition (relaxation). When muscles contract, they get tighter and do more work. When muscles relax, they do less work and allow their opposite muscles to contract better. Muscles in the body generally work in pairs.
Let’s use the examples of your biceps and triceps. Let’s imagine that you are sitting on a bench with a dumbbell in your right hand about to do a set of biceps curls. What happens when you move your right hand towards your shoulder? Place your left hand over your right bicep. In the rest position your biceps is pretty relaxed. The same with your triceps. Neither should feel tight or loose. Just relaxed. Now move that dumbbell up towards your shoulder and do a biceps curl. Now feel that biceps in the top hand position. Feels pretty tight now doesn’t it? The biceps muscle is contracting to pull the dumbbell towards your shoulder. Now feel the triceps. The triceps muscle should feel loose because it must relax in order for the biceps to contract. Now lower the dumbbell to the start position. The biceps muscle should be relaxed (loose) and the triceps contracted (tight). The same thing happens as you are running. As you lift your leg to propel yourself forward, your quadriceps (front of tight muscles) must contract to lift your knee forward and the hamstrings (back of thigh muscles) must relax. When the muscles are balanced in the body, they have the right combination of inhibition and facilitation during movement.
If muscles lack the right combination of inhibition and facilitation during movement muscle imbalances can occur. Muscle imbalances may lead to injuries, biomechanical inefficiencies, and wasted efforts. Muscle imbalances can also occur due to poor static posture, joint dysfunction, and myofascial adhesions (think “knot” in muscle). These altered length-tension relationships between muscles may lead to altered muscle recruitment patterns (altered force-couple relationships). This is caused by altered reciprocal inhibition. Altered reciprocal inhibition, defined by NASM, is the process by which a tight muscle (short, overactive, myofascial adhesions) causes decreased neural drive, and therefore optimal recruitment of its functional antagonist.
Let’s look at an example of this. A majority of people work 9-5 desk jobs in front of a computer. Thus they tend to have tight hip flexors, or iliopsoas muscles. Tight psoas muscles decrease the neural drive and therefore the optimal recruitment of gluteus maximus (your butt muscles). The gluteus maximus muscles are the prime movers for hip extension and an important muscle in running. According to a 2006 study in The Journal of Experimental Biology, the gluteus maximus works primarily to keep the torso upright during movement and it is involved in decelerating the swing leg as it hits the pavement. Since the glute is a hip extender muscle, it also functions to extend your hip-joint as your foot pushes off the ground to propel your body forward. Weaknesses in the gluteus maximus can lead to compensation and substitution by the synergists (hamstrings) and stabilizers (erector spinae). This can ultimately lead to potential hamstring strains and lower back pain.
According to one study, over the course of any given year approximately two-thirds of runners will have at least had one injury that has caused an interruption to their training. For those training for marathons, the rate as been recorded up to 90% of runners. The most common running injury involves the knee. The most common running related knee problems are patellofemoral pain syndrome, Iliotibial band (IT-Band) sydrome, tibal stress syndrome (spin splits), and plantar fasciitis. Guess what? These common running injuries are overuse injuries generally caused by muscle imbalances!
Some researchers and sports medicine professionals have argued that triathlon, as a multisport event, causes less overuse injuries than single sports, because of the more even distribution of loads over the body’s muscluar system. However, triathletes still suffer from a high degree of overuse injuries. One of the most common is actually lower back pain. Triathletes tend to be over-developed in larger muscle groups, such as the quadriceps, hamstrings, and shoulders. Triathletes tend to be weak in the smaller stability muscles, such as the lower back, core, adductors, and abductors. Again, these muscle imbalances are caused by movements that we do in each sport. For example, many triathletes, especially if they come from a cycling background, will be overdeveloped in the quadriceps region, but have these tiny, underactive hamstrings. This is a muscle imbalance caused by cycling. Runners are very weak in the hip stability muscles, such as the gluteus medius, tensor fascia latae (TFL), and adductor complex, which leads to weak lumbo-pelvic stability and the potential development of common running injuries. The sport of triathlon is conducted in one plane of motion – the sagittal plane. We rarely move in the frontal and transverse planes. Many of the hip stability muscles are targeted by movements conducted in the frontal and/or transverse planes.
Muscles can be divided into two types: postural and phasic. Postural muscles are used for standing and walking; whereas, phasic muscles are used for running. During the gait cycling of running, there is a double-float phase during which both legs are suspended in the air – one at the beginning and one at the end of the swing phase. Running biomechanics requires efficient firing patterns from the postural muscles while the phasic muscles do the actual work of propelling the body forward. Since the postural muscles are constantly be activated in the body to fight the forces of gravity, these muscles have a tendency to shorten and become tight. The postural muscles that tend to become chronically tight in runners are: gastroc-soleus, rectus femoris, ilipsoas, tensor fascia lata, hamstrings, adductors, quadratus lumborum, piriformis, and satorius. Phasic muscles typically may remain in an elongated or weak state. Common phasic muscle that have a tendency to be weak or become inhibited in runners are: the tibialis anterior, vastus medialis, long thigh adductors, and the gluteus maximus, medius, and minimus.
So, key points from this post:
- Muscle imbalances are caused by the lack of the right combination of contraction and relaxation of paired muscles
- Common triathlon and running injuries are generally caused by muscle imbalances, mainly in the lumbo-pelvic region
- Postural muscles tend to become short and tight; whereas phasic muscles tend to become weak and inhibited
- Stretch your psoas muscles! 🙂
Now, how do you identify muscle imbalances? Well, I did a post a while ago on why functional movement screens are important. Go read that! Or go see a sports medicine professional, such as a chiropractor or physical therapist. This is especially important if you are dealing with a common running-related injury. Then find yourself a good personal trainer to help set you up on a good strengthening routine to correct those imbalances. Remember, I am certified to help you correct muscle imbalances. Of course, you should always seek permission from your doctor before starting any new exercise routines. Stay tuned next week on some good hip stretching and strengthening exercises to help you prevent those pesky running injuries.
~ Happy Training!
PS – Feel free to contact me with any questions at firstname.lastname@example.org
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3. Liebermna DE et al. The human gluteus maximus and its role in running. J Exp Biol. 2006; 209: 2143-55.
4. Manninen JSO, Kallinen M. Low back pain and other overuse injuries in a group of Japanese triathletes. BR J Sports Med. 1996;30: 134-139.
5. Fredericson M, Moore T. Muscular balance, core stability, and injury prevention for middle – and long-distance runners. Phys Med Rehabil Clin N Am. 2005;16: 669-689.