Length-force characteristics of rat muscle during isometric contraction are determined by independent and cumulative effects of fatigue and potentiation

Effects of in vivo-like activation frequency on the length-dependent force generation of skeletal muscle fibre bundles

“…However, it is then unclear why no potentiation was found with CSF, because even with a continuous frequency of stimulation phosphorylation has been found to increase dramatically (Moore and Stull 1984). A possible explanation as to why potentiation was not found with CSF in the present work can be found in the work of Huijing and Roszek (1996): these authors have argued that interaction of fatigue and potentiation may obscure eects of myosin light chain phosphorylation at the lengths studied in the present work. Further studies at the cellular level are needed to explore the relative importance of both mechanisms in explaining the force potentiation observed with the DSF protocol.…”

Muscle, the motor of movement: properties in function, experiment and modelling

“…Few people realize that very complicated interactions between fatigue [1] and potentiation [69] are observed during sustained submaximal isometric contraction. It is argued [34] that the mechanisms of fatigue may even lead to an increase of force at higher muscle lengths (Fig. 13).…”

Length Dependent Potentiation in Electrically Stimulated Human Ankle Dorsiflexor Muscles

“…In contrast, for the SCI subjects, the DSF movements were always higher than the corresponding CSF values, which is in agreement with results on rat gastrocnemius muscles (2) showing always positive within burst potentiation decreasing with increasing muscle length. However, the same authors (11) pointed out that mechanisms leading either to enhancement (potentiation) or decrease (fatigue) in muscle force may have different relative importance at different muscle lengths. Therefore, independent, cumulative, and length dependent effects of these potentially counteracting mechanisms may account for the unexpected “negative potentiation” on healthy dorsiflexor muscles shown in this study.…”

“…For such applications it is essential to know the input‐output relationships of the muscular actuators, how they change during activation, and how previous stimulation influences muscle output. Furthermore, since muscle works over a range of lengths, it is important to investigate whether the same activation history may affect muscle performance in a length dependent manner (11).…”