Fiber Type Characteristics and Myosin Light Chain Expression in a World Champion Shot Putter

Introduction

Explosive strength is the major characteristic of the musculature of a champion shot putter. A shot putter would be expected to have a large muscle cross-sectional area and an increased proportion of fast (type II) fibers. Costill et al. [5] found 63 % fast twitch fibers in m. vastus lateralis biopsies from four shot putters and discus throwers. At the same time, it was noted that these “explosive” athletes had muscle fibers approximately twice the cross sectional area seen in untrained individuals (about 7700 μm² for type I and 9500 μm² for type II fibers). Similar values for both fiber type distribution and fiber size have also been reported for weight lifters [8] [21]. It is generally assumed that the fiber hypertrophy in these athletes is mainly a consequence of their training.

The opportunity arose to analyze muscle tissue from a world champion (1993) and Olympic medallist (1992) shot putter, W. Günthör (shot putter 1, names and abbreviations are used with the permission of the subjects). Biopsies were obtained from m. vastus lateralis at the time shot putter 1 stopped competing (November 1993) and three years later. As a comparison, biopsies were obtained from another world-class shot putter and long-term training companion (shot putter 2, himself a world class shot putter with a personal best of 21.01 m), and from the brother of shot putter 1, who never engaged in more than recreational sporting activities.

The contraction speed of a muscle fiber is determined by the isoform pattern of the contractile proteins. The prime determinant of contraction speed is the myosin heavy chain isoform, with type II myosins representing the fast myosin species. Success in shot put with the classic technique, as it was used by both shot putter 1 and 2, depends on the athlete's ability to generate a perfectly timed very high force that maximally accelerates the shot, i. e. very high power output, for which type II fibers are better suited than type I. A significant part of the training of world class shot putters is therefore directed towards the development of maximal explosive strength in limb extensor muscles, such as e. g. m. vastus lateralis.

This muscle is the preferred biopsy site in the majority of human studies because it is safe to sample with needles, for no major vessels or nerves transverse or lie adjacent to it. Fiber type composition and fiber size were analyzed using ATPase histochemistry. Based on previously described muscle fiber characteristics of shot putters (see above), it was hypothesized that these world class shot putters would also have a predominance of fast fibers and hypertrophy of both fiber types.

We also hypothesized that this type of training would also lead to shifts in the proportions of isoforms of the (many) myofibrillar proteins other than the myosin heavy chains, towards a faster phenotype. As an example, we investigated the distribution of the myosin light chain mRNAs in these athlete's fibers with in situ hybridization. Myosin light chains are thought to fine-tune the contractile properties of a fiber [14].

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