Bones, ligaments, tendons, cartilage, and fascia are illustrations of connective tissue. Exercise generates mechanical forces that cause distortion of precise regions of the skeleton. These forces, fashioned by muscular actions on the tendinous attachment into bone, can be bending, compressive, or torsional in nature. In reaction to mechanical loading, osteoblasts journey to the bone surface and initiate remodelling. Osteoblasts fabricate and discharge proteins, chiefly collagen molecules that are placed in the spaces between bone cells to increase strength. These proteins form the bone matrix and in due course become mineralised as calcium phosphate crystals. New bone formation occurs mainly on the outer surface of the bone (i.e., periosteum), augmenting diameter and strength. Muscle strength and hypertrophy gains intensify the force exercised on the bones.
Tougher forces of muscular contraction intensify the mechanical stress on bone, and bone must consequently increase in mass and strength to offer an adequate support structure for hypertrophied muscles. Accordingly, an increase in muscle strength or mass may end in a matching increase in bone mineral density, or the amount of mineral deposited in a given area of bone. The time course for bone alterations is rather long. Quantitatively augmenting bone mineral density via resistance training is a long-term progression, roughly six months or longer, and hinges on the construction of the resistance training programme. However, the process of adaptation begins within the first couple of workouts. The development of osteogenesis encompasses secretion of substances into the blood (substances specific to bone only) that can be evaluated. Thus, a rise in an osteogenic indicator is an early display of bone formation and seemingly a sign to increases in bone mineral density, so long as the stimulus is upheld over a long training period.
Baechle, Thomas R., and Roger W. Earle. NSCA Essentials of Strength Training and Conditioning. 2nd Edition. Champaign, Illinois: Human Kinetics, 2008.
Siff, Mel Cunningham, and Yuri Vitalievitch Verkhoshansky. Supertraining. 6th - Expanded Version. Denver: Supertraining International, 2009.