Cycle News - Archive Issues - 1980's

travel over nerve fiber at speeds up to about 200 miles per hour. The messages slo w to about 15 feet pe r seco nd (a bo u t 10 miles pe r h our ) wi th in a muscle group. Each muscle fi ber either co nt rac ts full y or doesn ' t contract. T he greater th e n u m ber of co n tracti ng fibe rs , the greater th e speed a nd stre ngth of the resulting movem ent. As fi ber co ntracts, a muscle gets sho rter a nd thi cker. The class ic exa mple is the bicep. Ge ne rally , a contra ct in g muscle ca n sho rten up to one-thi rd o f its resting len gth. T he speed of a co m plete contraction a n d relax at ion cycle may be as quick as a h undreth of a seco nd (with some eye m uscle ) or as slo w as a 10th o f a seco n d. Mu scle fibers co ntract in a n o rder lv sequ ence. The am ount of force needed, not th e speed o f co ntraction, co nt rols fiber recru itment: (I) Slow twit ch fiber s fire first. (2) Fast twitch fibers are recruited (the mo st Iargu e-resistant first ) if more force is needed. Contraction sequence Filaments within eac h muscle fiber slide over eac h other during co n trac tion ca usi ng th e muscle to thi cken and shorten . Exac tly how th is happens ha s not been verified , but th e followingexplanation is genera lly accep ted. (T h e book, T h e S wee t S pot in T im e by J ohn Jerome, details the process.) o Mu scle fiber s co nsist of two protein fi lamen ts - ac tin a n d m yosin - which overla p slig h tly. AT P is stored in th e cross bri dge area betwee n th e two type s of fila me nts . o T he acti n fila men ts have bi nd ing sites (so meth ing like ridges o n a bumper jack ) placed a t interva ls a lo ng their length. o The myosi n filament s have protru sion s (h eads) tha t reach toward the acti n bindi ng sites. o Mu scle activity is in itia ted when mo to r nerve con trac tio n signals a re received by the fibers. o Calci u m stored a ro un d the muscle fila me n ts is rele ased. T his electroc he mically charges the fila ment crossbridges. o The linkin g o f the cross bri dges ac tivates th e crea tio n of a tempor a ry p rot ein - actomyos in whic h triggers phosphate release from AT P present in the m uscle . o The energy from the phosphat e release allows the myosin heads to swive l toward a nd bind wi th actin binding sites in a ra tche ting process (like a bumper jack). T his p ulling or slid ing o f filam ents cont rac ts the muscle, mo vin g th e limb. o A relax ation signa l fro m th e ne rvous system withdraw s th e calcium and th e contractio n ends. o ATP , whi ch releases phosphate (p hosp ho ric acid )and energy as it breaks down, is replen ish ed by creatine phosphat e a lso stored in the muscle. T his replenishment a llows AT P to maintain the electrochemica l cha rging o f th e fil a ment crossbridges. (Muscles will lock if AT P resynthesizi ng is ins uffi cient. This is what causes rigor mortis, muscle rigidity in a corpse.) Muscle pairs Mu scles ca n pu ll, but th ey ca n ' t push. So , to produce lever- like bone mov ement a t a jo int, skel etal muscle grou ps wo rk as a team . Each assu me s one of two rol es, th e o p posi te of its partner during a ny movem ent. o Agon ist - co ntrac ts to move a bone. o A ntagonist - relaxes to all ow the bone to move. The coo rd ina ted movement of muscle pairs eliminates what would other- wise be jerky and imprecise movements. Muscle pairs then swap ro les to reverse the ac tion. For exa mple, th e bicep (agon ist) contracts as the tricep (ant agon ist) lengthens to a llo w a n arm cu rl. Then th e tricep contracts to straigh ten the arm as the bicep relaxes a nd lengthens . Curl in g a wei ght req u ires £Iexion a nd ex tension activity by the in volved muscles. These, howeve r, are not the o n ly ro les pl ayed by various muscles: o Flexion. A flexor muscle mo ves two con necti ng bones toward eac h o ther. o Ex tension. An ex tensor m uscle straig htens th e al ign me nt oftwo con necti ng bones. o A bduction. An a bd uctor m uscle mo ves a li m b away from the center of th e bod y. o A dduc tion . An adduc to r muscle moves a lim b towar d the cen ter of th e bod y. o R otation . A rotator muscle turns a bone in a circular motion at i ts joint. Some muscles serve mor e th an one Iunct ion, For exa m p le, th e thigh muscles stra ig h ten the leg a t th e kn ee (kn ee extens io n ) a nd bend th e upper leg (hi p £Iexi on) to ward th e bod y. Muscular growth c hemistry ( I) S t ress . Contra ctin g muscl e agai nst resis ta nce initia tes che mical respo nse t ha t s t im u la tes fu tu re growth. It is believed the increased prod uctio n o f creatine p hosph a te triggers th e p roduction o f addi tional contraction protein wi thin th e fiber . (2) R est. Recovery time a fter stress a llo ws for the repa ir of mi no r tissue damage and the growth o f th icker fiber (h ypertrop h y). . (3) Nu trit ion , a ba la nced diet provides the nutrients necessary to both fue l the stress exercise a nd no urish muscle grow th. T h icker m uscle fiber is stronger muscle fiber , just as an inch-thick rope is stronger tha n a half-in ch rope. T he capillary networ k within the muscle a lso grows , increasi ng the loca l blood su p ply. Mu scular growth a lso stim u la tes a n in crease in myoglobin (used for o xyge n picku p ) as well as the storage of muscle g lycoge n. Use it or lose it Unfortu nat ely, m uscles are n ot like money. You ca n work hard , deposit your do llars in a ba n k, collect interest, a nd use you r cas h at a ny time in th e future. With muscles, ho wever , th e depo sit or loses his principal. Rath er ra pi dly. La ck o f stress leads to muscular atrophy, th e loss o f blood volume a nd cont rac ti ng protein s. T h is muscle sh ri n kage ca n beg in a fter four da ys of in activity. In a yea r' s time, tot all y in ac tive m uscl e can lose as much as 75%of its volume. It is estimated th at a two-month la yoff can harm the efforts of years o f tra in ing . That 's wh y serious a th letes ar e u rged to use som e form of o ffseason train ing to maintain muscle tone or minimize a trophy , Muscle may shri n k, bu t it does not turn to fat. Muscle is muscle. However , mo re fat may be storedabove sh rin king mu scle, especia ll y if an a th lete do esn ' t red uce his ca lor ies as he reduces h is exercise, • Cham pionship Tra in ing , by Dean Mi llet and L en W eed , includes Brad L ackey 's complete year-'rou n d train ing p rogram as we ll as in -dep th f itnes s and train ing inform ation fo r all sports, 112 pages, over 80 p hotos and illustrations. To order, send $9.95 p lus $1.50 postage and handling to C leans heet Enterpr ises, P,O . Box 24I C, T arzana, CA 91356. Califo rn ia residents add 65( sales tax. ( T o be contin ued next wee k) ATVlIell1$ TM Covers it all! All that's happening in the world of allterrain vehicles. Every month. All for only $5 a year. A TV News, America's ' A 11- Terrain Vehicle Newspaper. Subscribe today! AMERICA'S MONTHLY ALL-TERRAIN VEHICLE NEWSPAPER ••••••••••••••••••••••••••••••••••••• o YES! Send me one full year (12 issues) of ATV NEWS for only $5.00! o I want to SAVE MORE! 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