It's crucial to lift weights at a time when the body is best prepared to handle the tremendous amount of stress that action places on the lumbar spine. For most people, this time will be in the afternoon or evening as the spine is up to 20 percent stronger than when you wake up.
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Rest in the Morning
Overnight, the spine lengthens and accumulates spinal fluid. This can make maximal effort lifts or twisting unsafe for the lower back. Unfortunately, there isn't much you can do to speed up the compression of the spine except wake up earlier. If you're already working out early, do a thorough warmup that includes five to 10 minutes on the treadmill plus dynamic stretches like inchworms, spiderman lunges, and walking toe touches.
Big Effort in the Evening
During the day, the spine naturally compresses due to gravity. The spine will safely flex 5 percent more than in the early morning hours. This makes it ideal to lift weights later in the day if you plan on doing any movements that can create large amounts of compressive and shearing forces. This can include exercises like deadlifts, squats, and any twisting movements.