Phasic fibers are characterized by a higher content of glycogen (+ 14, + 44%), creatine phosphate (+ 26, + 66%), creatine (+ 15%), total protein (+ 14%) and higher ATPase activity (3, 5 times), creatine kinase (+10, +55%), phosphorylase (4 times), aldolase (10 times), enolase (10 times), glycerol aldehyde phosphate dehydrogenase (almost 9 times), pyruvate kinase (5 fold), lactate dehydrogenase (2-fold) and -glycerophosphate dehydrogenase (15-fold). Finally, the content of ATP, ADP, AMP, myosin, and actin in both types of muscle fibers is the same.
All these properties of muscle fibers are not strictly fixed once and for all. In different functional conditions, they can vary. For example, as a result of systematic exercise with various loads in the muscle, the chemical properties characteristic of phasic or tonic fibers may increase (456). With denervation, the muscles lose their specific properties of phasic or tonicity (874, 903). Experiments with cross innervation (stitching of the central end of the nerve to the tonic muscle, with the peripheral end of the nerve going to the phasic muscle, and vice versa) show that both the contractile and many chemical properties of muscles change, the tonic muscles acquire a number of properties of phasic , and vice versa (546, 607, 874, 903).The only exception is the “white” and “red” muscles of domesticated birds and animals.
There is no direct correlation between the content in myoglobin muscle and its functional profile (397, 419, 456), and therefore the terms “red” and “slow-growing” in the scientific literature, “hardy”, muscle (and therefore “white” and rapidly shrinking) are not are identical. The specialization of skeletal muscles is determined by the totality of their functional and biochemical properties, but not by color.