25 - 30 %
||Rat Rattus norvegicus
||Menshikova EV et al., Effects of exercise on mitochondrial content and function in aging human skeletal muscle. J Gerontol A Biol Sci Med Sci. 2006 Jun61(6):534-40. p.534 right column top paragraphPubMed ID16799133
|| Krieger DA, Tate CA, McMillin-Wood J, Booth FW. Populations of rat skeletal muscle mitochondria after exercise and immobilization. J Appl Physiol. 1980 48: 23–28.  Bizeau M, Willis W, Hazel J. Differential responses to endurance training in subsarcolemmal and intermyofibrillar mitochondria. J Appl Physiol. 1998 85: 1279–1284.PubMed ID6444398, 9760317
||P.534 right column top paragraph: "Sub-sarcolemmal (SS) mitochondria reside near the sarcolemma, and inter-myofibrillar (IMF) mitochondria are located between the myofibrils. It has been suggested that SS mitochondria provide energy for membrane related events including cell signaling, substrate and ion transport, while IMF mitochondria supply ATP to
contracting myofibrils (ref 12). SS mitochondria generally represents only 25–30% of the total amount of skeletal muscle mitochondria but appear to be more responsive to increased physical
activity in rat muscle (primary sources) as well as in young human skeletal muscle (refs 14–16). Whether
there are improvements in specific mitochondrial subpopulations in older adults with reduced mitochondria content and function has yet to be determined."