What is a tilted pelvis?
A pelvic tilt is a fairly common postural problem. A pelvic tilt occurs when the pelvis tilts in one direction. An anterior pelvic tilt is when the pelvis tilts towards the front of the body and a posterior pelvic tilt in which the pelvis tilts towards the back of the body. The anterior pelvic tilt is the most common of the two in upright posture. Pelvic tilts are usually due to muscle imbalances. In other words, certain muscles may not be working properly and other muscles may be working too much.
From a mechanical/structural component, an anterior pelvic tilt causes some muscles to be tight and others to be lengthened. Specifically, the hip flexor (in the front of the pelvis) and lower back muscles become shortened because they are positioned in a shortened state and the hamstring (muscles in the back of the pelvis) and abdominals, become lengthened due the pelvis being tipped forward. (Fig 1)
Figure 1: In a standing position the tilt of the pelvis has a direct impact on the resting length of the hamstring muscle
A common misconception in this position (anterior pelvic tilt) is that the hamstrings appear to be short and tight and need to be stretched. The hamstrings are actually lengthened and tense secondary to the pelvis falling forward and need to be activated to return the pelvis to a more neutral position. Often times patients with low back pain and tightness (which can be related to an anterior tilt) are often told to stretch their hamstrings to relieve their discomfort. In response to stretching of the hamstrings, the pelvis may tilt even further forward and the lower back becomes tighter as the back muscles are overactive in attempt to bring the upper body back into an upright position.
In response to stretching the hamstrings, the pelvis may tilt even further forward and the lower back muscles may become tighter to keep the body upright
We often hear our patients complain about how tight they are, especially how tight their hamstrings are. These individuals often times struggle to bend over to touch their toes, and it seems that everyone’s advice is to stretch those “tight” hamstrings! Most often individuals think their hamstrings need to be stretched because they have a sensation of tightness. However, there are two types of tightness; mechanical and neurological. It is important to differentiate between the two and understand why stretching the hamstrings often times won’t fix the problem, and why they need to strengthen the hamstrings, as they play an important role in stabilizing and positioning the pelvis.
Mechanical tightness occurs when a muscle is positioned in a constant shortened state, which causes the muscle to become physically shorter and increasingly tight over time. Neurological tightness, occurs from a muscle being held constantly in a lengthened position for an extended period of time. When a muscle is placed in a lengthened position, it receives additional signals from the brain (a stretch reflex), which is thought to be a protective response from the body to prevent the muscle from being stretched too far. These increased neural signals is what creates the sensation of tightness. So the muscle may “feel” tight in a shortened or lengthened position which is why addressing the position first is necessary before addressing the sensation of tightness.
Straight Leg Raise
The straight leg raise assessment is when the straight leg is passively lifted toward the head and the degree of movement is assessed. The end point nearly all of the time for a straight leg raise is the sensation of hamstring tightness. However, the degree to which the leg can be moved is more directly related to the position of the pelvis than to the “tightness” of the hamstring. A normal finding for a “neutral” pelvic tilt is a straight leg raise of 90 degrees. The hamstring will feel tight at that position. (Fig 2)
Fig 2: Typical straight leg raise findings with a neutral pelvic tilt
Think back to the anterior pelvic tilt which places our lower back in an arched position, or an increase in lumbar lordosis. When the clinician lifts the leg to assess the straight leg raise, the hamstring becomes taut at an earlier point then it should because the muscle is already pre-tightened due to the position of the pelvis (anterior pelvic tilt). In other words, the leg won’t go as far because it’s already being stretched before it even moves. This limited leg raise would be expected and typical for a pelvis that is tilted forward without an actual change to the hamstring muscle length. (Fig 3)
Fig 3: Typical straight leg raise findings with an anterior pelvic tilt
If the hamstring muscle actually becomes overstretched, the leg raise will look excessive but there is often still a sense of hamstring “tightness” at a position that would not be considered normal. This muscle is now actually long and weak and its ability to “tighten” enough to control the anterior tilt of the pelvis is severely limited and the anterior tilt and its associated symptoms, including lower back pain, will be harder to manage. This is a non-typical finding of an anterior pelvic tilt and much harder to manage. (Fig 4)
Fig 4: Atypical (pathological) findings of straight leg raise with an anterior pelvic tilt
What does this mean?
From a clinical standpoint, “tight” hamstrings do not necessarily mean short hamstrings, which means stretching is actually not the right thing to do. Instead of stretching, which is usually recommended due to the sensation of tightness, the hamstrings actually need to be strengthened to return the pelvis to a more neutral/optimal position first.
One should focus less about an individual muscle or muscle group as it relates to the sensation of tightness, and instead think in terms of the position in which the muscle is held! Positionally, the tightness may be felt in the hamstrings but the hamstring is not shortened—it is lengthened! It is related instead to the position of the pelvis or anterior pelvic tilt.
Individuals may claim they cannot touch their toes due to their hamstrings feeling “tight”, however, stretching these already lengthened hamstrings may bring about potential injuries to the pelvis, lower back, and knee. Instead focus on strengthening the hamstrings to reposition the pelvis to a more neutral position in order to restore proper mechanics around the pelvic girdle. The position of the pelvis plays a vital role in how the spine above it and the femur (thigh bone) below it will function. It would be fair to say that an abnormal position of a structure will result in an abnormal movement of that respected structure
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