The effects of ischaemia and overload on muscle mass and fibre size över time.

Purpose: Extensor digitorum longus (EDL) and extensor hallucis proprius (EHP) muscles were overloaded in Ischaemic and normal muscle in order to determine how muscle hypertrophy occurred under these conditions, and to vvhat extend fibres of different size in the same muscle responded to overload during different time courses. Methods: İn this experiment 87 male rats were used and divided into control (C), ischaemic (I) achieved by unilateral ligation of the common iliac artery, overloaded (O) achieved by unilateral ablation of the synergist tibialis anterior, and overloaded plus ischaemic (O+l) groups. Histological analysis was performed on cryostat sections. Results: İn EDL hypertrophy occurred at the same level during the first 4 vveeks (P<0.05 vs. O), while in the smaller EHP hypertrophy occurred progressively över this time (P<0.01). After 6 vveeks, hypertrophy of the EDL was clearly greater than at earlier time points. İn the EDL muscle the response to hypertrophy was greatest in the smaller muscle fibres (P<0.01). VVhile hypertrophy was not signlficant in the larger fibres, atrophy was significant during ischaemia (P<0.01). VVhen overloaded muscle was made ischaemic there was less hypertrophy compared to non-ischaemic muscle during the first 4 weeks but it reached the same level by 6 vveeks, possibly due to angiogenesis in this time. Conclusions: There was greater hypertrophy in the smaller muscle vvhen a synergist muscle was removed, and there was also greater hypertrophy in the smaller fibres vvithin same muscle. İt is postulated that in order to prevent atrophy and stimulate angiogenesis in the ischaemic muscle, as vvas shovvn in the O+l muscle, careful exercise is reçuired although possible pain during the initial period may limit the response.