Sprint training, in vitro and in vivo muscle function, and myosin heavy chain expression

Abstract

. Sprint training, in vitro and in vivo muscle function, and myosin heavy chain expression. J. Appl. Physiol. 84(2): 442-449, 1998.-Sprint training represents the condition in which increases in muscle shortening speed, as well as in strength, might play a significant role in improving power generation. This study therefore aimed to determine the effects of sprint training on 1) the coupling between myosin heavy chain (MHC) isoform expression and function in single fibers, 2) the distribution of MHC isoforms across a whole muscle, and 3) in vivo muscle function. Seven young male subjects completed 6 wk of training (3-s sprints) on a cycle ergometer. Training was without effect on maximum shortening velocity in single fibers or in the relative distribution of MHC isoforms in either the soleus or the vastus lateralis muscles. Electrically evoked and voluntary isometric torque generation increased (P Ͻ 0.05) after training in both the plantar flexors (ϩ8% at 50 Hz and ϩ16% maximal voluntary contraction) and knee extensors (ϩ8% at 50 Hz and ϩ7% maximal voluntary contraction). With the shortening potential of the muscles apparently unchanged, the increased strength of the major lower limb muscles is likely to have contributed to the 7% increase (P Ͻ 0.05) in peak pedal frequency during cycling. contraction; exercise THE INCREASE IN MUSCLE POWER generation that results from training could be brought about by at least two different mechanisms. First, it can be brought about by an increase in the force-producing capability of the muscle, either through increased activation or through an increase in muscle size. Second, it can occur by increasing the speed at which a muscle can shorten against a given load.A close coupling exists between the speed of muscle shortening and the expression of the different myosin heavy chain (MHC) isoforms. Muscle fibers that express the MHC-I isoform exhibit significantly slower maximal velocities of shortening (V o ) (24, 28) and power outputs (11) compared with fibers expressing the two fast MHC isoforms. Within the subgroups of fast isoforms, fibers that express the MHC-IIB isoform [which has recently been shown to be homologous to the MHC-IIX isoform found in small mammals (18,34)] are significantly faster (24, 28) and can generate higher power outputs than fibers containing the MHC-IIA isoform (11,36). Muscle speed of movement could be increased either by altering the relative expression of the fast and slow isoforms or by changing the coupling between isoform expression and function.

Effects of resistance training on myosin function studied by the in vitro motility assay in young and older men

“…In young subjects, contradictory results have been obtained. No change in V o was observed after resistance (42) or sprint (22) training, whereas an increase in V o was observed after a decrease in swim training volume (37).…”

“…Trappe et al (40) showed a resistance-training related increase in V o of both slow-and fast-twitch muscle fibers in elderly men, but not in elderly women (39). In young subjects, no changes in V o have been observed after resistance (42) or sprint training (22), whereas an increase in V o was observed after swim taper, i.e., a change in training volume (37). Notwithstanding some inconsistencies, collectively the latter findings indicate that V o of single muscle fibers can indeed change with no change in myosin isoform content at least in some subject groups and some experimental conditions.…”

Effect of 6�weeks of sprint training on growth hormone responses to sprinting

“…The greater blood lactate response to exercise following sprint training suggests increased glycolytic flux (Nevill et al 1989;Stathis et al 1994), and reduced plasma ammonia following training might be the result of an increased glycolytic rate. However, improvements in sprint performance following a short period of training are most likely a result of the recruitment of a larger muscle mass through neural adaptations (Harridge et al 1998).…”

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

“…In this regard our findings support suggestions that the IIB fibres reported in previous studies are of the IID(X) phenotype. Furthermore recent studies indicate that most of the MHCIId(x) isoform is expressed in the IIA fibre population forming a population of hybrid IIA/ IID(X) fibres (e.g., Gur et al 2003;Harridge et al 1998;Widrick et al 2002). We used a panel of monoclonal antibodies that allowed direct identification of pure type Ib and IIA fibres, as well as hybrid I/IIA fibres.…”