Effects of 84-days of bedrest and resistance training on single muscle fibre myosin heavy chain distribution in human vastus lateralis and soleus muscles

AIM: This investigation determined the effects of 84 days of bedrest on the composition of myosin heavy chain (MHC) in single skeletal muscle fibres with and without a resistance-training countermeasure programme. METHODS: Muscle biopsies were obtained from the m. vastus lateralis (VL) and m. soleus (SOL) before and after 84 days of bedrest. While control (BR) subjects (VL n = 9; SOL n = 3) refrained from exercise, BRE subjects (VL n = 8; SOL n = 3) performed knee extensor and plantar flexor resistance exercise every third day. Approximately 110 fibres per sample were analysed for MHC composition using SDS-PAGE. RESULTS: BR-VL had 16 and 14% decreases (P < 0.05) in MHC I and IIa fibres, respectively. There were 10% increases (P < 0.05) in MHC I/IIa, IIa/IIx, I/IIa/IIx, and a approximately 30% increase (P < 0.05) in total hybrid fibres. BRE-VL showed a 15% reduction (P < 0.05) in MHC I fibres, no change in MHC IIa fibres, and a 13% increase (P < 0.05) in total hybrids. BR-SOL had a 19% decrease (P < 0.05) in MHC I fibres with a 22% increase in total hybrids. BRE-SOL showed no change in MHC composition across all fibre types. CONCLUSION: These data suggest that the exercise countermeasures programme prevented MHC shifts in the SOL and mitigated MHC shifts in the VL. Furthermore, in the VL it appears that the resistance training programme employed in this investigation during bedrest, emphasized the use of MHC IIa phenotype muscle fibres.     

Contractile properties and myosin heavy chain isoform composition in single fibre of human laryngeal muscles

In the present study we aimed to determine the functional properties and the myosin heavy chain (MHC) isoform composition of single chemically skinned fibres from the vocal muscle of four adult men (age: 55–67 years). Single fibres, dissected from the bioptic samples, were chemically skinned and isometric tension (P ₀) and maximal shortening velocity (V ₀) were measured at pCa 4.6. MHC and myosin light chain (MLC) composition of fibre segments and MHC distribution of the biopsy samples were analysed by SDS–poly-acrylamide gel electrophoresis (SDS—PAGE) and densitometry. Four MHC isoforms (1, 2A, 2X and a fourth isoform, provisionally called L) and five MLC isoforms (MLC1s, MLC1f, MLC3f, MLC2f, MLC2s) were identified. The major findings of this study were: (1) fast MHC isoforms (in particular MHC-2A) and fast fibres were predominant, (2) one-third of the fibres were mixed or hybrid, i.e. expressed more than one MHC isoform, (3) V ₀ and P ₀ values were determined by the MHC isoform composition and mixed fibres showed functional properties which were intermediate between pure fibres; MHC-L was associated with V ₀ values similar to those of MHC-2A, (4) compared with limb muscles, V ₀ values of laryngeal fibres were similar to those of limb muscle fibres containing the same MHC isoform whereas P ₀ values were lower for slow and fast 2X fibres and similar for fibres expressing MHC-2A.     

Cortisone-induced changes in myosin heavy chain distribution in respiratory and hindlimb muscles

In this study the effects of administration of cortisone acetate (100 mg kg^-1 body weight subcutaneously for 11 days) on distribution and cross-sectional area of different fibre types of rat skeletal muscles were investigated. Diaphragm, parasternal intercostal (PI), extensor digitorum longus (EDL) and soleus muscles were examined in cortisone treated animals (CA) in comparison with ad libitum controls (CTRL) and pair-fed (PF) controls. Four fibre types (I or slow and IIA, IIX, IIB or fast) were identified on the basis of their myosin heavy chain composition using a set of monoclonal antibodies. In CA rats the reduction of cross-sectional area was above 30% in IIX fibres of diaphragm, IIB fibres of PI and in all fast fibres of EDL. In all muscles slow fibres were spared from atrophy. Significant variations in fibre type distribution were found in the muscles of CA rats when compared to CTRL. The percentage of IIB fibres decreased in EDL, PI and diaphragm. This decrease was accompanied by an increase in the percentage of IIA fibres in the same muscles. No changes in the percentage of slow fibres and of fast IIX fibres were observed in EDL, PI and diaphragm of CA rats in comparison with CTRL. In soleus of CA rats the proportion of IIA fibres was lower than in CTRL. In EDL of PF rats atrophy of IIA fibres and changes in fibre type distribution were similar to those observed in CA rats. In diaphragm, PI and soleus of PF rats no significant decrease in fibre cross-sectional area nor significant changes in fibre distribution were found in comparison with CTRL rats.     

Mechanical measures during maximal velocity knee extension exercise and their relation to fibre composition of the human vastus lateralis muscle

Summary A method for measuring the maximal velocity of knee extension exercise is described using a very light lever arm. Instrumentation of the lever arm with a potentiometer and accelerometer also allows for the measurement of peak acceleration, time to peak acceleration, the average rate of development of acceleration (jerk) and peak torque. With this apparatus and surface electromyography, electromechanical delay (EMD) was also determined. This apparatus was tested using 17 female and 10 male subjects, and the measures obtained were related to the percentage of fast twitch fibres (% FT) and the relative area of fast twitch fibres (% FTA) in the vastus lateralis determined from duplicate muscle biopsy samples. Peak velocity of unloaded knee extension averaged 12.1±1.2 and 12.2±1.7 rad · s^–1 for females and males, respectively, and were not significantly different. As well, peak acceleration, time to peak acceleration jerk and EMD values were not significantly different between the female and male subjects, but the mean peak torque for the female subjects (73.5±14.7 N · m) was significantly lower than that for the males (98.4±31.5 N · m). Peak acceleration was significantly correlated with %FT (r=0.40,P=0.04) for the total subject population. None of the other measures was significantly related to either %FT or %FTA for the male and female subjects or the combined population of subjects.     

Relationship between myosin heavy chain IId isoform and fibre types in soleus muscle of the rat after hindlimb suspension

Summary The relationship between the myosin heavy chain (HC) IId isoform and histochemically defined fibre types was investigated in the rat soleus muscle after hindlimb suspension. After 4 weeks of suspension, right and left muscles were removed and fibre type composition and total fibre number were examined by histochemical myosin adenosine triphosphatase staining sections. Myosin HC isoforms were analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis. After the suspension, there was a significant decrease in the percentage of type I fibres and a concomitant increase in that of type IIa fibres. However, the total number of fibres was not affected by suspension. The synthesis of HC IId isoform, which was not found in the control, and the decrease in the ratio of slow type myosin heavy chain isoform (HC I) were observed after suspension. These results would may suggest that the change of fibre type composition was caused by a shift from type I to IIa fibres after suspension. Furthermore, it could be suggested that the synthesis of HC IId isoform occurred during the stage of type shift from type I to IIa fibres.     

Immunohistochemical changes in the expression of HSP27 in exercised human vastus lateralis muscle

Aim: The role of HSP27 in the adaptive process of skeletal muscle to exercise, especially in humans, is not well understood. The objective of this study was to investigate immunohistochemical changes in HSP27 expression in human vastus lateralis muscle following resistance and endurance exercises. Methods: Two different exercise protocols were used: (1) one‐leg ergometer cycling (EC, n = 6) consisting of two 30‐min bouts at 40% and 75% of peak oxygen uptake, respectively, and (2) leg extension resistance exercise (RE, n = 9) including 10 sets of eight repetitions at a load corresponding to 70% of one maximal repetition (1RM). Immunohistochemistry using specific monoclonal antibodies was used to determine the location of HSP27 protein in muscle biopsies from human vastus lateralis. Results: Our results show that RE, but not EC, induced a significant appearance of scattered accumulations of HSP27 protein in muscle fibres from five of nine subjects. The number of fibres with accumulation of HSP27 in RE ranged from 0% to 32% with a mean of 6.3% of the total number of fibres. Conclusion: We conclude that this rapid HSP27 protein relocation after RE is an important player in the cellular remodelling of human muscle fibres in response to exercise involving high‐force contractions, but not in response to endurance exercises.     

Myosin heavy chain isoforms in single fibres from m. vastus lateralis of sprinters: influence of training

The myosin heavy chain (MHC) composition of single fibres from m. vastus lateralis of a group of male sprint athletes (n= 6) was analysed, before and after a three months period of intensive strength- and interval-training, using a sensitive gel electrophoretic technique. Significant improvements were observed after training in almost all of a series of performance tests. After training the sprinters revealed a decrease in fibres containing only MHC isoform I (52.0 ±3.0% vs. 41.2 ±4.7% (mean±SE) (P < 0.05)) and an increase in the amount of fibres containing only MHC isoform IIA (34.7 ±6.1% vs. 52.3 ±3.6% (P < 0.05)). Fibres showing co-existence of MHC isoforms IIA and IIB decreased with training (12.9 ± 5.0% vs. 5.1 ±3.1%, (P < 0.05)). Only one out of 1000 fibres analysed contained only MHC isoform IIB. In contrast, a higher amount of type IIB fibres (18.8 ± 3.6% vs. 10.5 ± 3.9%, (P < 0.05)) was observed with myofibrillar ATPase histochemistry. The majority of histochemically determined type IIB fibres of sprinters seems therefore to contain both MHC isoforms IIA and IIB. Sprint-training appears to induce an increased expression of MHC isoform IIA in skeletal muscles. This seems related to a bi-directional transformation from both MHC isoforms I and IIB towards MHC isoform IIA.     

Differential modulation of myosin heavy chain phenotype in an inactive extensor and flexor muscle of adult rats

The effects of chronic neuromuscular inactivity on the phenotype and size of muscle fibres in a fast ankle extensor (medial gastrocnemius, MG) and a fast ankle flexor (tibialis anterior, TA) muscle of the rat hindlimb were determined. Inactivity was produced by spinal cord isolation (SI), i.e. complete spinal cord transections at a mid-thoracic and high sacral level and bilateral deafferentation between the transection sites. After 90 days of SI, the MG and TA muscle weights were 53 and 45% lower than in age-matched controls. Overall mean fibre sizes in the deep (close to the bone) and superficial (away from the bone) regions were approximately 60 and 65% smaller in the MG and approximately 40 and 50% smaller in the TA of SI than control rats, respectively. The myosin heavy chain (MHC) composition shifted towards the faster isoforms after SI: the MG showed an increase in both types IIx (20%) and IIb (23%), whereas the TA showed a marked increase in type IIx (94%) and a decrease in type IIb (18%) MHC. Both muscles in SI rats showed no type IIa and only one MG muscle had approximately 5% type I MHC. These results show that prolonged inactivity has a stronger effect on a fast extensor compared with a fast flexor in the rat hindlimb. The larger decrease in mass and fibre size in the MG than the TA most probably reflects the larger impact of chronic inactivity on the normally more highly recruited extensor than flexor muscle. The primary shift to type IIb MHC in the MG and type IIx MHC in the TA indicate a different default mode for an inactive extensor vs. flexor muscle, and may reflect differing activity-independent neural influences, i.e. neurotrophic factors, on muscle fibre phenotype in extensors vs. flexors.     

Energy state and myosin heavy chain isoforms in single fibres of normal and transforming rabbit muscles

 Energy-rich phosphates, [ATP]/[ADP_free] ratios, and the myosin heavy chain (MHC) complement were determined in single fibres from normal rabbit muscles, and in fibres isolated from tibialis anterior muscle undergoing fast-to-slow conversion by chronic low-frequency stimulation (CLFS). In normal muscles, energy-rich phosphate contents and [ATP]/[ADP_free] ratios could thus be assigned to different MHC-based fibre types. Phosphocreatine (PCr) contents and [ATP]/[ADP_free] ratios differed markedly between fast- and slow-twitch fibres, as well as within the fast fibre subtypes. Both magnitudes were approximately twofold higher in the fastest (type IIB) fibres as compared to the slowest (type I) fibres. According to PCr contents and [ATP]/[ADP_free] ratios pure and hybrid fibres were aligned in an order similar to that determined by their contractile properties and myofibrillar ATPase activities. CLFS for up to 30 days induced pronounced decreases in PCr and [ATP]/[ADP_free] which attained levels twofold lower than in normal slow-twitch fibres. In both normal and stimulated muscles, PCr and [ATP]/[ADP_free] ratios were correlated, indicating their equilibrium in the different fibre types. The relationship detected between MHC isoform expression and the [ATP]/[ADP_free] ratio suggests that the drastic and persistent depression of the cellular energy state may act as an important signal initiating fast-to-slow transformation processes in muscle fibres. Received: 26 June 1998 / Accepted: 31 July 1998     

Effects of eccentric overload training on patellar tendon and vastus lateralis in three days of consecutive running

Background

The analysis of structural changes in patellar tendon and muscle of healthy subjects in response to mechanical loads provides useful insight into the mechanism underlying overuse injuries.

Effects of eccentric and concentric muscle actions in resistance training

The adaptive responses to two different resistance training regimens were compared. Healthy males performed five sets of either 12 maximum bilateral concentric (Grp CON; n = 11) or six pairs of maximum bilateral eccentric and concentric (Grp ECCON; n = 11) quadriceps muscle actions three times per week for 12 weeks. Uni- and bilateral eccentric and concentric peak torque at various angular velocities, vertical jump height and three-repetition maximum half-squat were measured before and after training. Muscle biopsies were obtained from m. vastus lateralis and analysed for fibre type composition and area using histochemical techniques. In contrast to a control group (n = 7), performing no training, Grps CON and ECCON demonstrated marked increases (P < 0.05) in overall eccentric (19 and 37% respectively) and concentric (15 and 26% respectively) peak torques. Grp ECCON, however, showed greater (P < 0.05) increases in peak torque, vertical jump height and three repetition maximum than Grp CON. The 7% increases in slow-twitch fibre area in Grps CON and ECCON and in fast-twitch fibre area in Grp CON were nonsignificant. This study suggests that increases in peak torque and strength-related performance parameters were greater following a programme consisting of maximum concentric and eccentric muscle actions than resistance training using concentric muscle actions only. Because increases in muscle fibre areas were small it is also suggested that the increased muscle strength shown subsequent to short-term accommodated resistance training is mainly due to neural adaptation.     

Correlation of dystrophin–glycoprotein complex and focal adhesion complex with myosin heavy chain isoforms in rat skeletal muscle

Aim: The dystrophin–glycoprotein complex (DGC) and focal adhesion complex (FAC) are transmembrane structures in muscle fibres that link the intracellular cytoskeleton to the extracellular matrix. DGC and FAC proteins are abundant in slow‐type muscles, indicating the structural reinforcement which play a pivotal role in continuous force output to maintain posture for long periods. The aim of the present study was to examine the expression of these structures across fast‐type muscles containing different myosin heavy chain (MHC) isoform patterns which reflect the fatigue‐resistant characteristics of skeletal muscle. Methods: We measured the expression of dystrophin and β1 integrin (representative proteins of DGC and FAC respectively) in plantaris, extensor digitorum longus, tibialis anterior, red and white portions of gastrocnemius, superficial portion of vastus lateralis and diaphragm, in comparison with soleus (SOL) and cardiac muscle from rats. Results: The expression of dystrophin and β1 integrin correlated positively with the percentage of type I, IIa and IIx MHC isoforms and negatively with that of type IIb MHC isoform in fast‐type skeletal muscles, and their expression was abundant in SOL and cardiac muscle. Conclusion: Our results support the idea that DGC and FAC are among the factors that explain the fatigue‐resistant property not only of slow‐type but also of fast‐type skeletal muscles.     

Effects of stretch-shortening cycle training on mechanical properties and fibre type transition in the rat soleus muscle

The effects of exercise training on mechanical properties and fibre type transitions have been investigated in rat soleus muscle. The exercise was a repetition of stretch-shortening cycles. A method of dual controlled releases was applied to obtain tension/extension curves, which characterize the elastic behaviour of the series elastic component (SEC), and the force/velocity relationship characterizing the contractile elements. Other contractile measurements included: contraction time (t _c), half-relaxation time (t _1/2) and twitch/tetanus ratio (P _t/P _o). Additionally, the muscle fibre type composition was determined by a classical histochemical method. A 12-week period of training induced a significantly higher percentage of fast-twitch fibres and a lower percentage of slow-twitch fibres (P<0.01). This fibre adaptation led to a significant (P<0.01) decrease in t _c and an increase in maximum shortening velocity (V _max). An increase in compliance of the SEC was also observed. This elastic adaptation is interpreted in terms of modification of the active components of the SEC. All the histochemical and mechanical data presented in this study show that rat soleus muscles trained by stretch-shortening cycles acquired faster characteristics. Thus the results confirm that a slow-twitch to a fast-twitch fibre transition is obtainable in mature rats.     

Effects of hypobaric hypoxia on histochemical fibre-type composition and myosin heavy chain isoform component in the rat soleus muscle

Histochemical fibre-type composition and myosin heavy chain isoform component in the soleus muscle were studied in normoxic rats at postnatal ages of 5, 10, 15, and 20 weeks and in rats exposed to hypobaric hypoxia (460 torr) for 5 weeks from postnatal ages of 5, 10, and 15 weeks. The increase in the percentage of type I fibres and the concomitant decrease in that of type IIa fibres in the soleus muscle of normoxic rats were observed until 15 weeks of age. On the other hand, no change in the fibre-type composition of the muscle during postnatal development was observed in hypoxic rats, irrespective of the age at which they were exposed to hypoxia. The changes in the myosin heavy chain isoform component (MHC I and MHC IIa) of the muscle during postnatal development and by hypoxia corresponded well with those in the muscle fibre-type composition. It is concluded that hypobaric hypoxia inhibits the growth-related shift of muscle fibre-types from type IIa to type I and of myosin heavy chain isoforms from MHC IIa to MHC I in the rat soleus muscle, and that there are no changes in the muscle fibre-type composition or the myosin heavy chain isoform component caused by hypoxia after the shifts in these parameters which occur during postnatal development are completed.     

Hindlimb suspension induces the expression of multiple myosin heavy chain isoforms in single fibres of the rat soleus muscle

The aim of our experiment was to test the hypothesis that the performance of maximal isometric exercise every 20 s would reduce the intermediate frequency force, i.e. the force that appears while stimulating the muscle at 15 and 20 Hz, and would produce less decrease the force at 10 and 50 Hz, while Pt would increase. Such changes in stimulated force should demonstrate the coexistence of potentiation, low frequency fatigue (LFF) and `post-contractile depression' (PCD). The quadriceps muscle of 14 healthy men (aged 19–37 years) was studied. The results have shown, that during isometric exercise of maximal intensity there was significant (P < 0.05) decrease in P15 and P20, increase in Pt, however, MVC and P10 and P50 was unchanged (P > 0.05). LFF manifested itself most significantly which is evident from decrease in P20/P50. During recovery after work there was significant increase in LFF and decrease in P50 which is indicative of the manifestation of PCD. Besides, there was significant (P < 0.05) decrease immediately after exercise in RTP20 and RTP50, while no changes in T50 and RT. There were no significant changes (P > 0.05) however, either in RTP20 and RTP50 or in T50 and RT 20 min after exercise if compared to the initial and immediately post-exercise values.     

Myosin heavy chain isoform transformation in single fibres from m. vastus lateralis in spinal cord injured individuals: Effects of long-term functional electrical stimulation (FES)

The myosin heavy chain (MHC) composition of single fibres from m. vastus lateralis of five spinal-cord-injured (SCI) individuals was analysed by Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) before, and after 6 and 12 months of functional electrical stimulation (FES)-training, administrated for 30 min three times per week. Prior to FES training 37.2% of the fibres contained only MHC HB, 21.2% only MHC IIA, and 40.7% co-expressed MHC IIA and MHC IIB. After 6 months of FES-training the number of fibres containing only MHC IIB was reduced to 2.6% (P < 0.05), the number of fibres containing only MHC IIA was increased to 44.3 (P < 0.05), and the number of fibres co-expressing MHC IIA and MHC HB was 50.9% (ns). After 12 months almost all fibres (91.2%,P < 0.05) contained only MHC IIA. The number of fibres containing only MHC IIB was 2.3 % and the fibres co-expressing MHC HA and HB had decreased to 4.6% (P < 0.05). The amount of fibres containing only MHC I never exceeded 0.5%. Likewise, the number of fibres co-expressing MHC I and MHC IIA was below 2% throughout the study period. In total, the MHC composition of 1596 single fibres was determined. This study shows that FES-training of paralysed human skeletal muscle administrated over a prolonged period of time, can lead to a marked switch in MHC expression from about equal amounts of MHC HA and MHC HB to an almost total dominance of MHC HA.     

Postnatal transitions in myosin heavy chain isoforms of the rabbit superficial masseter and digastric muscle

We investigated the early (< 8 weeks) and late (> 8 weeks) postnatal development of the fibre type composition and fibre cross-sectional area in the superficial masseter and digastric muscle of male rabbits. It was hypothesized, first, that due to the transition between suckling and chewing, during early postnatal development the increase in the proportion of slow fibre types and in fibre cross-sectional areas would be larger in the masseter than in the digastric; and second, that due to the supposed influence of testosterone during late postnatal development, the proportion of slow fibre types in both muscles would decrease. Fibre types were classified by immunostaining according to their myosin heavy chain (MyHC) content. The proportion of slow fibre types significantly increased in the masseter, from 7% at week 1 to 47% at week 8, and then decreased to 21% at week 20, while in the digastric it increased from 5% in week 1 to 19% at week 8 and remained the same thereafter. The changes in the proportion of fast fibre types were the opposite. The remarkable increase and decrease in the proportion of slow fibre types in the masseter was attributed predominantly to MyHC-cardiac alpha fibres. During early development, the cross-sectional area of all fibres in both muscles increased. However, only the fast fibre types in the masseter continued to grow further after week 8. Before weaning, the fast fibre types in the digastric were larger than those in the masseter, but after week 8, they became larger in the masseter than in the digastric. In adult animals, masseter and digastric had the same percentage of fast fibre types, but these fibres were almost twice as large in masseter as in digastric.     

Adverse changes in fibre type and myosin heavy chain compositions of human jaw muscle vs. limb muscle during ageing

This review shows that human jaw muscles not only have unique fibre type and myosin heavy chain (MyHC) compositions but also undergo muscle and region-specific changes in fibre composition during ageing. Alterations in the masseter and the lateral pterygoid muscles in the elderly are opposite to those reported for limb and trunk muscles, whereas changes in the anterior and posterior bellies of the digastric muscle resemble those of limb and trunk muscles. We conclude that age-related alterations in fibre type composition and MyHC expression are muscle and region specific, probably reflecting muscular differences in genetic programs and epigenetic influences.     

Effects of strength, endurance and combined training on myosin heavy chain content and fibre-type distribution in humans

This study investigated the effect of strength training, endurance training, and combined strength plus endurance training on fibre-type transitions, fibre cross-sectional area (CSA) and MHC isoform content of the vastus lateralis muscle. Forty volunteers (24 males and 16 females) were randomly assigned to one of four groups: control (C), endurance training (E), strength training (S), or concurrent strength and endurance training (SE). The S and E groups each trained three times a week for 12 weeks; the SE group performed the same S and E training on alternate days. The development of knee extensor muscle strength was S>SE>E (P<0.05) and has been reported elsewhere. The reduction in knee extensor strength development in SE as compared to S corresponded to a 6% increase in MHCIIa content (P<0.05) in SE at the expense of the faster MHCIId(x) isoform (P<0.05), as determined by electrophoretic analyses; reductions in MHCIId/x content after S or E training were attenuated by comparison. Both S and SE induced three- to fourfold reductions (P<0.05) in the proportion of type IIA/IID(X) hybrid fibres. S also induced fourfold increases in the proportion of type I/IIA hybrid fibres within both genders, and in a population of fibres expressing a type I/IID(X) hybrid phenotype within the male subjects. Type I/IIA hybrid fibres were not detected after SE. Both S and SE training paradigms induced similar increases (16–19%, P<0.05) in the CSA of type IIA fibres. In contrast, the increase in CSA of type I fibres was 2.9-fold greater (P<0.05) in S as compared to SE after 12 weeks. We conclude that the interference of knee extensor strength development in SE versus S was related to greater fast-to-slow fibre-type transitions and attenuated hypertrophy of type I fibres. Data are given as mean (SEM) unless otherwise stated.