By Bridget End, PT, DPT. Have you ever been told that you have a weak gluteus maximus (aka glute max) muscle, despite doing tons of bridges and deadlifts to strengthen them? If your answer is yes, then there is an underlying cause of the supposed glute max weakness. While there can be numerous causes, a common cause is tight hip flexors (including the iliopsoas and rectus femoris). The hip flexors are the antagonists to the gluteus maximus, meaning they perform the opposite motion (hip flexion vs. hip extension). If your hip flexors are so tight that they are limiting your full hip extension range of motion, then your gluteus maximus is unable to move your hip into enough hip extension to have the proper length-tension relationship of the muscle fibers to optimally contract and achieve maximal force. Thus, you will not benefit as much from your glute strengthening exercises, nor will you be able to fully engage your glute max in every day life, which as with running, walking or simply standing. Why are my hip flexors tight? The hip flexors often get tight from sitting for long periods of time (e.g. with a desk job, travelling in a car or plane, cycling). Unless you counteract all of this sitting with hip flexor stretching, over time, the seated position can lead to what’s known as the “lower crossed syndrome”. In this scenario, our hip flexors and lower back muscles become tight and over-active, while our glute max and abdominals become over-stretched and inhibited. These muscular imbalances result in an excessive anterior (forward) tilt of the pelvis, impaired core stability, and further muscular imbalances down the chain, throughout the entire lower extremity. The tighter certain muscles get, the more inhibited their antagonistic muscles get, which results in a vicious cycle of all of the muscles getting tighter and tighter. Ultimately, lower crossed syndrome can lead to low back, hip and pelvic pain, as well as lower extremity injuries further down the leg. Even if you do not have pain, from a sports performance standpoint, it can result in decreased efficiency with running, as you are unable to fully access your glute max to push off and propel you forward. How do I fix this? The good news is that your body is adaptable and can return to optimal posture and muscle function. You can do so by stretching your hip flexors in conjunction with core strengthening / lumbar stabilization exercises. Since the psoas, a major hip flexor, originates from the lumbar spine, it provides stability for the spine. When the psoas gets tight from sitting, it pulls the lumbar spine into hyper-lordosis, which tightens the low back muscles and inhibits the abdominals, causing them to weaken over time. So, when you stretch and loosen the psoas, you also need to incorporate exercises to retrain the abdominals and low back muscles to work synchronously to stabilize the spine in its most natural and efficient posture. Once you have rebuilt a more stable core, you have a strong foundation to begin to address lower extremity weaknesses, including glute max weakness. If you think you may be struggling with lower crossed syndrome, I suggest contacting a physical therapist, in order to learn the appropriate stretches and stability exercises to improve your posture and overall function.