Characteristics and adaptation of skeletal muscle to endurance exercise

Kohn, Tertius A. (2011-10)

Thesis (PhD)--University of Stellenbosch, 2005.

Thesis

ENGLISH ABSTRACT: Skeletal muscle adapts to stimuli by modifying structural and metabolic protein expression. Furthermore, a muscle group may vary within itself to accommodate specialisation in regions. Structural and metabolic characteristics of an individual are regulated partly by genotype, but contraction duration and intensity may play a greater role in muscle phenotype. The aims of this dissertation were to investigate: structural and metabolic regionalisation in a muscle group, possible relationships between training volume and intensity and hybrid fibres, muscle characteristics of athletes from two different ethnic groups, and muscle adaptation in already well-trained athletes subjected to high intensity interval training. Myosin heavy chain (MHC) isoform content and citrate synthase (CS) activities were measured in the Quadriceps femoris (QF) muscle of 18 female rats. Muscle was divided into superficial, middle and deep, distal, central and proximal parts. MHC IIb and IIx were more abundant in superficial regions (P < 0.05) with low CS activities compared to deeper parts. Isoform content varied along the length of deep regions. This study showed that the QF has regional specialisation. Therefore, standardisation of sampling site is important. Hybrid fibre proportions in muscle biopsies of 12 middle distance runners and 12 non-runners were investigated. MHC IIa/IIx correlated with training volume/week in runners (r = -0.66, P < 0.05) and MHC IIa/IIx correlated with exercise hours/week in non-runners (r = -0.72, P < 0.01). Average preferred racing distance (PRDA) correlated better with MHC IIa/IIx in runners (r = -0.85, P < 0.001). MHC IIa/IIx may therefore be more closely related to exercise intensity than previously thought. Fibre type characteristics and performance markers were investigated in 13 Xhosa and 13 Caucasian distance runners, matched for performance, training volume and PRDA. Xhosa runners had less MHC I and more MHC IIa fibres in muscle biopsies than Caucasian runners (P < 0.05). Xhosa runners had lower plasma lactate at 80% peak treadmill speed (PTS) (P < 0.05), but higher lactate dehydrogenase (LDH) (P < 0.01) and phosphofructokinase (P = 0.07) activities in homogenate muscle samples. LDH activities in MHC I (P = 0.05) and IIa (P < 0.05) fibre pools were higher in Xhosa runners. Xhosa athletes may thus have a genetic advantage or they may have adapted to running at a higher intensity. Six weeks of individually standardised high intensity interval treadmill training (HIIT) were investigated in 15 well-trained runners. PTS increased after HIIT (P < 0.01), while maximum oxygen consumption (VO2max) only showed a tendency to have increased as a result of HIIT (P = 0.06). Sub-maximal tests showed lower plasma lactate at 64% PTS (P = 0.06), with lower heart rates at workloads from 64% to 80% PTS (P < 0.01) after HIIT. No changes were observed for cross-sectional area, capillary supply and enzyme activities in homogenates muscle samples. LDH activity showed a trend (P = 0.06) to have increased in MHC IIa pools after HIIT. Higher HIIT speed was related to decreases in MHC I fibres, but increases in MHC IIa/IIx fibres (r = -0.70 and r = 0.68, respectively, P < 0.05). Therefore, HIIT may alter muscle fibre composition in well-trained runners, with a concomitant improvement in performance markers.

AFRIKAANSE OPSOMMING: Skeletspier kan adapteer deur strukturele en metaboliese protein ekspressie te verander as gevolg van stimulante. ‘n Spiergroep kan ook intern verskil om spesialisering in spierdele toe te laat. Strukturele en metaboliese karaktereienskappe van ‘n individu word deels gereguleer deur gene, maar kontraksie tydperk en intensiteit mag ‘n groter rol speel in spierfenotipe. Die doelwitte van hierdie tesis was om ondersoek in te stel in: strukturele en metaboliese eienskappe in spiergroepstreke, moontlike verhoudings tussen oefeningsvolume of intensiteit en baster vesels, spier eienskappe in atlete van twee etniese groepe, en spier adaptasie in goed geoefende atlete blootgestel aan hoë intensiteit interval oefening. Miosien swaar ketting (MSK) isovorm inhoud en sitraat sintase (SS) aktiwiteite is gemeet in die Quadriceps femoris (QF) spier van 18 wyfie rotte. Spiere was opgedeel in oppervlakkig, middel en diep, asook distaal, sentraal en proksimale dele. MSK IIb en IIx was meer oorvloedig in oppervlakkige dele (P < 0.05) met lae SS aktiwiteite in vergelyking met dieper dele. Isovorm inhoud het ook verskil oor die lengte van diep dele. Dus bevat die QF gespesialiseerde streke en is die area van monsterneming belangrik. Baster vesel proporsies is ondersoek in spiermonsters van 12 middel afstand hardlopers en 12 niehardlopers. MSK IIa/IIx van hardlopers het met oefeningsvolume/week gekorreleer (r = -0.66, P < 0.05), asook MSK IIa/IIx van nie-hardlopers met oefeningsure/week (r = -0.72, P < 0.01). Gemiddelde voorkeur wedloop afstand (VWAG) het beter met MSK IIa/IIx gekorreleer in hardlopers (r = -0.85, P < 0.001). MSK IIa/IIx mag dus meer verwant wees aan oefeningsintensiteit. Veseltipe eienskappe en prestasie merkers was ondersoek in 13 Xhosa en 13 Caucasian langafstand atlete, geëweknie vir prestasie, oefeningsvolume en VMAG. Xhosa hardlopers het minder tipe I en meer tipe IIA vesels in hul spiermonsters gehad as die Caucasian hardlopers (P < 0.05). Xhosa hardlopers het laer plasma laktaat by 80% van hul maksimale trapmeul spoed (MTS) (P < 0.05), maar hoër laktaat dihidrogenase (LDH) (P < 0.01) en fosfofruktokinase (P = 0.07) aktiwiteite in homogene spiermonsters gehad. LDH aktiwiteite in MSK I (P = 0.05) en IIa (P < 0.05) veselbondels was hoër in Xhosa hardlopers. Xhosa atlete mag dus ‘n genetiese voorsprong geniet, of hulle het geadapteer om by hoër intensiteite te hardloop. Ses weke van geïndividualiseerde gestandardiseerde hoë intensiteit interval trapmeul oefening (HIIT) was ondersoek in 15 goed geoefende hardlopers. MTS het verhoog na HIIT (P < 0.01), en maksimale surrstof verbruik (VO2max) het ‘n neiging getoon om te verhoog het na HIIT (P = 0.07). Submaksimale toetse het laer plasma laktaat by 64% MTS getoon (P = 0.06), met laer harttempos by werkladings 64% tot 80% MTS (P < 0.01). Geen veranderings was gemerk vir deursnit area, kapillêre toevoer en ensiem aktiwiteite in homogene spiermonsters nie. LDH aktiwiteit het ‘n neiging getoon om te verhoog het (P = 0.06) in MSK IIa veselbondels na HIIT. Hoër HIIT snelhede was verwant aan ‘n daling in MSK I vesels, maar ‘n verhoging in MSK IIa/IIx vesels (r = -0.70 en r = 0.68, respektiwelik, P < 0.05). HIIT mag dus spier veseltipe verander in goed geoefende hardlopers, met gevolglike verbetering in prestasie merkers.

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