A few comments..
Physiatrists really do not know how to treat lower back pain except with medications and Depo medrol cortisone shots (facet joint shots or epidural shots.) Yes, if done correctlu, it will take the inflammation down immdeately, but it is not addressing the PRIMARY cause of the inflammation..
As I have posted in other threads here, muscle spams are a 2ndacry and REACTIONARY response to other primary causes. Muscles do not just spontaneously spasm by themselves. Spasms are either from the actual soft tissue over use, injures, or a protective spasm as a result of pain from other structures such as the faet joints, nerve roots, discs, ligaments, etc, etc. When a cliinician tells you that your muscles are in spasm and stops right there, he or she does NOT know what is causing your lower back pain. A good clinician will take the exam further, and find out if the muscle spasm is caused but over used from poor posture/body mechanics (palpation and mechanical exam), muscle injury from a traumatic injury (palpation and mechanical exam, and for very advanced practices, utra sound imaging), disc issues (MRI), facet issues (x rays), etc, etc.... If he or she just prescribes medication either orally or by a shot and end there, your lower back pain likely will come back inthe future because the primary cause of the musclle spasm has not yet be identified. Muscle spasm is not a specific diagnosis, it is a description of a sympton.
As far as exercises, one member above mentioned "abs" and "obliques." Most people do not realize that there are 2 layers of the abdominals: outter and inner. The trunk/spine stabilization muscles are mostly the multifdus and the abdominal transverse, the inner layer of the abdomial muscle group. The outter layer of the abdominal do not stabilize the spine, but raher performs trunk flexion and rotation. These are the rectus and obliques. These muscles actually will increase your intra-abdominal pressure when they are engaged. This is HORRIBLE for your torn discs! That is why when you ahve a disc problem, any activities that contract these outter layers of abdominals such as sneezing, coughing, or straining on a bowle movement will "throw your back out." This is one of the standard questions we ask our patients with lower back pain (if your MD or PPT is not asking this questions, that is not a really good sign.) So, performing exercises taht recruit outter layers of abdominals are actually VERY BAD for an acute diac problem. After the discs are healed (yes, discs heal, facet DJD do not), then you can perform these eercies that involve the outter layers of abominial muscles.
Also, running is BAD for acute discogenic impairments, but OK if your core is strong and your discs healed. It puts a lof of axial presure on the lumbar and cervical spines due to the curvatures in these 2 areas (L4-L5 and C5-C6), which are actually designed as areas of shock absorbers. If you sitll have any signs of back or neck pain, running is not a good thing to do...