If your hips are killing you, you probably spend a lot of time sitting—in the car, at work, on that SoulCycle seat—which puts your hips in near-constant "flexion", says Cori Lefkowith, NASM-certified personal trainer and owner of Redefining Strength in Orange County, California. Even running involves a repetitive flexion movement that can cause pain.
Back pain can suck the joy out of your days for week, months, even years. It can definitely be “serious” even when it’s not dangerous. I have worked with many truly miserable chronic low back pain patients, and of course the huge economic costs of back pain are cited practically anywhere the subject comes up. But your typical case of chronic low back pain, as nasty as it can be, has never killed anyone.
Work on strengthening all of your core muscles and glutes. These muscles work together to give you balance and stability and to help you move through the activities involved in daily living, as well as exercise and sports. When one set of these muscles is weak or tight, it can cause injury or pain in another, so make sure you pay equal attention to all of them.
In order to treat this hip and leg pain, it is important to understand the causes of lower back pain. Amongst people below the age of 60, the most common cause of sciatica is a slipped or herniated disc, in the lower lumbar region of the spine. When a disc is swollen or has moved, it puts pressure on the sciatic nerve, causing discomfort and pain. This tends not to happen instantly, but instead generally develops over time. Other causes include:
Acute back pain is often the result of muscle sprains or strains. Sprains occur when your ligaments are overstretched and sometimes torn. Strains, on the other hand, are caused by stretching — and possible tearing — of your tendons or muscles. Though the immediate reaction is pain in your back, you may also experience dull aches or discomfort in your hip.
John Wolf is Onnit's Chief Fitness Officer, and an expert in unconventional training methods such as kettlebell, steel club, and suspension training. With 15-plus years of experience in the fitness industry, he has worked with rehab clients and athletes of all levels. He moves like Spider Man and can deadlift more than 500 pounds any day of the week.
Approximately 15 degrees of hip extension is required to walk normally. If hip flexors are tight then in order to walk, compensatory movement needs to take place through the lower back causing back pain and premature disc degeneration. Like other joints, if we fail to take them through their full range on a regular basis we eventually lose mobility.
Arthritis is a common cause of radiating lower back pain. Symptoms include back pain that fluctuates, coming and going throughout the day and night and numbness in the neck area, as well as stiffness and lack of mobility. Recommended treatment for arthritis of the back includes heat, ice, rest, exercising and stretches, and over the counter anti-inflammatories. In severe cases, patients seek surgery but sometimes, surgery does more harm than good.
Tight hip flexors can result in lower back pain, hip pain and injury.  A lot of strain is put on those muscles during activities that involve sprinting and kicking.  For example, runners are more prone to hip flexor injuries because of the small, repetitive movement during running.   But even if you’re not an athlete, hip flexor injuries can occur during everyday activities (for instance, slipping and falling or running to catch a bus).  When those tight muscles are suddenly stretched beyond what they are accustomed to, you might also experience pain in the upper groin region, typically where the hip meets the pelvis.   
Lay on your back on your mat and pull your knees to your chest. Place your hands on the inside arches of your feet and open your knees wider than shoulder-width apart. Keeping your back pressed into the mat as much as possible, press your feet into hands while pulling down on feet, creating resistance. Breathe deeply and hold for at least 30 seconds.
Good points on isolating the single joint hip flexors and avoiding compensations. I am curious about your perspective (and others) on why this is less likely to stress the anterior capsule? I tend to add trunk side ending before finalizing the stretch to bias the psoas. The stretch you have outlined seems like an iliacus and ant. capsule biased stretch. Thoughts? If I really want to protect the anterior capsule, I’ll also add a slight amount of hip internal rotation.
At the very least, the tension and/or spasm in muscles that cross over the hip and attach onto the pelvis can contribute to imbalance, in terms of how strong and flexible each muscle group is in relation to the others. But muscle imbalance in the hips and the spine may make for pain, limitation and/or posture problems. It can also increase the healing challenge put to you by an existing injury or condition, for example, scoliosis.
Both types of problems are frequently helped by anti-inflammatory medications particularly in mild to moderate situations. Some types of analgesics can be used intermittently as well. It's important to realize that both problems can be helped significantly by weight loss, proper forms of exercise and conditioning. In fact, back pain can become chronic without a commitment to the appropriate exercises necessary to stabilize and strengthen the spine. Epidural blocks (corticosteroids are injected into the canal of the low back to reduce inflammation and pain) can help several types of back disorders. Using a cane when walking can help both hip and back pain.
You're more likely to get a hip flexor injury if you've had one in the past, you don't warm up properly before engaging in athletic activity, your muscles are already tight or stiff, or your muscles are weak from being overused. If, while exercising, you try to do too much at once in too short an amount of time, you can also put yourself at risk for a hip flexor injury.
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