Rapid regeneration of power stroke in contracting muscle by attachment of second myosin head

When Lombardi and colleagues reported the phenomenon of rapid regeneration of the power stroke after a quick release of a muscle fibre during a tetanus, they gave an explanation in terms of detachment of cross-bridges and re-attachment further along the thin filament. We show here that the phenomenon can also be explained on assumptions that lead to a majority of myosin molecules being attached by only one head during steady isometric contraction; the other head may then become attached after a quick release and can add its contribution to the early tension recovery after a second release.