The gluteus maximus (also known collectively with the gluteus medius and minimus, as the gluteal muscles, and sometimes referred to informally as the "glutes") is the main extensor muscle of the hip. It is the largest and most superficial of the three gluteal muscles and makes up a large portion of the shape and appearance of each side of the hips. Its thick fleshy mass, in a quadrilateral shape, forms the prominence of the buttocks.
This phase continues to employ a four-day split, but bodyparts are paired differently—namely, chest and back are trained on the same day (Day 1), as are biceps and triceps (Day 4). This is little more than a means of changing things up, giving your muscles a slightly different stimulus to spark new muscle growth. Each workout includes drop sets to increase intensity, but for only one set per bodypart, so as to avoid overtraining and muscle catabolism.
Lie on your left side and position yourself so that your bottom forearm is directly under your armpit and your legs are straight with feet stacked. Brace your core and lift your hips in the air, forming a straight line from ankles to shoulders. Next, raise your top leg, without bending your knee, a few inches into the air. Hold for 3-5 seconds, lower the leg, and repeat. Complete required reps then switch sides.
Grade III (severe): A complete tear in your muscle that causes severe pain and swelling and you can't bear weight on that leg, making it difficult to walk. You've also lost more than 50 percent of your muscle function. These injuries are less common and may need surgery to repair the torn muscle. They can take several months or more to completely heal.
Learning to activate your glutes is important so that you can strengthen them. Strong glute muscles are extremely important as these muscles can have a major impact on your overall body strength; your glutes support your core, help to support a range of exercises and compound movements, as well as help avoid muscle imbalances which can lead to decreased mobility. 
It has been argued that purposely overtraining for a brief period can be beneficial. One article published by Muscle & Fitness magazine stated that you can "Overtrain for Big Gains". It suggested that if one is planning a restful holiday and does not wish to inhibit their bodybuilding lifestyle too much, they should overtrain before taking the holiday, so the body can recuperate and grow during the prolonged rest period. Overtraining can be used advantageously, as when a bodybuilder is purposely overtrained for a brief period of time to super compensate during a regeneration phase. These are known as "shock micro-cycles" and were a key training technique used by Soviet athletes.[53]
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