II. Tim vai van dong
B. Khoi luong mau duoc tong ra a moi lan trai tim bop
(dung luong bop cua tim)
Dung luong mau gom tich so' cua hai so luong : khoi luong mau duoc day ra moi lan tim co bop va so lan co bop cua tim trong mot phut. Khoi luorng mau nay la so luong mau bi day ra ngoai tu moi mot buong ciia trai tim khi tim dap, nghia la sau moi mot lan co bop ciia trai tim. 6 mot ngucri Ion thi khoi luomg mau do trong khi binh thuorng la 40 den 60 mililit, nhung van dong vien luyen tap hoac nhting nguoi lao dong nang thi co cao horn, khoang chting 100 den 120 mililit.
Nhu da noi, liru luorng mau trong khi lam viec cao dp thi co the tang len nhieu lan, nghia la dat tori hem 40 lit mau trong mot phut. Nhung khoi luong mau chi co the tang do hem hai lan, mac du su tang len it nhung do cung la da thuc hien hoan thanh mot nhiem vu to 1cm. Qua quan sat moi buong tim da cho thay sau moi mot lan tim bop thi khoi luong mau chua dung trong tim da duoc day ra ngoai (hinh 1), mat khac lien sau do, mot khoi lucmg mau moi lai tiep tuc chay vao.
Duong nhien la sir tang miic co gian ciia buong tim khong the qua Ion duoc. Gian ra duoc gap hai lan la mot nang luc rat Ion va la dac diem cho ta thay ro them nhung so lieu sau day : vi du trong luc mot nguoi lao dong hay mot van dong vien yen tinh, khoi luong mau tong ra moi lan co bop cua trai tim or moi nguoi la 100 mililit, nhung khi co van dong lao dong thi tang len hai lan khoi luong cua mau do, nghia la 200 mililit.
Theo nhiing so lieu da nghien cuu nhieu truong hop cua G.I.Marocopskia thi khoi luong mau to'ng ra moi lan co bop cua trai tim a cac cong nhan lao dong va van dong vien luyen tap thticmg xuyen cac mon the thao nang co the tang len khong nhting den 200 ma co the toi 220 mililit. Doi vdi nhting ngiroi khong luyen tap, khong lao dong thi
khoi luong mau do trong khi lam viec thuong khong qua 120 den 160 mililit la cung.
Khoi luong mau tong ra moi lan tim bop rat Ion do la 6 nhung nguoi lao dong nang nhoc va nhung van dong vien luyen tap cuong do Ion thudng gan lien vOi do Ion cua trai tim. Kich thuoc cua trai tim co the duoc quy dinh, can ban b in g hai truong hop :
1. B in g nhiing kich thuoc cua ben trong buong trai tim trong khi gian ra.
2. B in g do to cua nhung buc tuOng chu vi ben trong cua chung, la be day cua thanh tim. Nhiing buong tim mor rong ra de co the chua dung duoc rat nhieu mau, cung voi hien tuong do, de cho khoi luong mau tang len thi trai tim phai co bop nhanh chong de day mau vao he thong dong mach, do do no phai co nhiing bap thit khoe manh.
Mot nguo’i binh thuong va mot van dong vien biet ren luyen hop ly ve tuan hoan va ho hap thi sue manh cua cac co tim khi kiem tra thuong thuong tuong xung vdi do to cua chung, va su luyen tap van dong deu se anh hudng den do day cua thanh tim, do do se tang sue manh co bop cua tim, dieu do dac biet anh hudng nhieu tdi cac bap thit cua tam that trai. Do cung la mot yeu to thich hop de no co du kha nang hoan thanh cong viec day mau vao trong he thong tuan hoan ldn. Nhiing bap thit cua tam that phai cung duoc tang len, nhung so vdi tam that trai thi it hon vi rang no day mau vao he thong nho cua bo
may tuan hoan. Nhimg tat ca nhiing yeu to hop dong van hanh ciia ca hai tam that trai va phai deu can thiet phai co de tang ciiOng siic manh ciia tim, de day duoc nhiing khoi mau nhieu bat thuong them len trong cac cuoc van dong, lao dong va thi dau the thao.