Eccentric Exercise: Physiological Characteristics and Acute Responses

Abstract

An eccentric contraction involves the active lengthening of muscle under an external load. The molecular and neural mechanisms underpinning eccentric contractions differ from those of concentric and isometric contractions and remain less understood. A number of molecular theories have been put forth to explain the unexplained observations during eccentric contractions that deviate from the predictions of the established theories of muscle contraction. Postulated mechanisms include a strain-induced modulation of actin-myosin interactions at the level of the cross-bridge, the activation of the structural protein titin, and the winding of titin on actin. Accordingly, neural strategies controlling eccentric contractions also differ with a greater, and possibly distinct, cortical activation observed despite an apparently lower activation at the level of the motor unit. The characteristics of eccentric contractions are associated with several acute physiological responses to eccentrically-emphasised exercise. Differences in neuromuscular, metabolic, hormonal and anabolic signalling responses during, and following, an eccentric exercise bout have frequently been observed in comparison to concentric exercise. Subsequently, the high levels of muscular strain with such exercise can induce muscle damage which is rarely observed with other contraction types. The net result of these eccentric contraction characteristics and responses appears to be a novel adaptive signal within the neuromuscular system.

Hormonal responses following eccentric exercise in humans

“…Such potential interactions between hormones and other secreted proteins could therefore be part of an integrated system of signalling to mediate and support physiological adaptations to muscle mechanical overloading and damage, 9 hence, the net result of eccentric exercise-induced hormonal, metabolic and anabolic responses appears to be a novel adaptive signal within the muscle. 10 However, although much has been learned about the local mechanisms and the cellular and molecular interactions that mediate muscle regeneration and adaptation following exercise-induced muscle damage, [11][12][13][14] the role of systemic, and particularly hormonal, responses to muscle damage and its subsequent adaptations is still not fully defined. Only a limited number of studies have examined the acute exercise-induced hormonal responses following mechanical overloading (resistance exercise) or muscledamaging eccentric exercise in humans, 9,[15][16][17] while in those studies only few hormones, such as cortisol, testosterone or growth hormone (GH), have been investigated and this only for a short period of time, i.e.…”

Muscle length matters: new insights into the neural control of lengthening muscle actions of the knee extensors

“…The molecular and neural mechanisms underlying lengthening muscle actions are less understood and differ from those of constant‐length and shorting contractions (Enoka, ; Douglas et al . ).…”

“…The mechanisms discussed for the greater force production during lengthening muscle actions include, inter alia , the mechanical detachment and the increased number of cross‐bridges (Douglas et al . ). However, the force‐generating capacity of human muscles during lengthening muscle actions in vivo is usually comparable or only slightly higher compared with constant‐length and slow shortening contractions.…”

“…Lengthening muscle actions typically occur during the stretch-shortening cycle, while lowering a weight and during the braking phase of movements. The molecular and neural mechanisms underlying lengthening muscle actions are less understood and differ from those of constant-length and shorting contractions (Enoka, 1996;Douglas et al 2017).…”

“…Data from animal studies have impressively demonstrated that the performance capacity of muscle fibres is usually 50-80% higher for lengthening muscle actions compared with constant-length and shortening contractions (Duchateau & Enoka, 2016). The mechanisms discussed for the greater force production during lengthening muscle actions include, inter alia, the mechanical detachment and the increased number of cross-bridges (Douglas et al 2017). However, the force-generating capacity of human muscles during lengthening muscle actions in vivo is usually comparable or only slightly higher compared with constant-length and slow shortening contractions.…”