Stretching the limits of maximal voluntary eccentric force production in vivo

•Maximum voluntary eccentric forces can exceed maximum isometric forces at the same muscle length by a factor of 1.2–1.4, provided that the experimental conditions result in active fascicle stretch during the eccentric contractions.•Muscle fascicle length, velocity, and stretch amplitude all interact to determine voluntary eccentric force capacity.•Apparent neural inhibition during maximal voluntary eccentric contractions has not been confirmed under conditions where eccentric forces exceed isometric forces at identical muscle length.•The reduction in voluntary eccentric force capacity relative to the eccentric forces obtained from electrically stimulated contractions and from isolated muscle preparations remains unclear. During eccentric contractions, muscular force production capacity is enhanced compared to isometric contractions. Although this is well accepted in terms of muscle mechanics, maximal voluntary eccentric contractions are associated with neural inhibition that prevents increased force production of in vivo human muscles. However, because it was shown that maximal voluntary eccentric forces can exceed maximum isometric forces by a factor of 1.2–1.4, this review focuses on the question of whether the absent eccentric force enhancement, as observed in many studies, can unambiguously be attributed to an inherent neural inhibition. First, we demonstrate that participant familiarization, preload, and fascicle behavior are crucial factors influencing maximal voluntary eccentric force production. Second, we show that muscle mechanics such as muscle length, lengthening velocity, and stretch amplitude interact when it comes to maximal voluntary eccentric force production. Finally, we discuss the diverging findings on neural inhibition during maximal voluntary eccentric contractions. Because there was no inhibition of the major motor pathways in the presence of enhanced maximal voluntary eccentric forces, further research is needed to test the concept of neural inhibition and to understand why maximal voluntary force production is reduced compared to the force capacity of isolated muscle preparations.