Effect of knee joint position on triceps surae motor unit recruitment and firing rates

Hali, Kalter; Kirk, Eric A.; Rice, Charles L.

doi:10.1007/s00221-019-05570-7

Cited by 13 publications

(10 citation statements)

References 31 publications

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“…For this, we recorded maximal voluntary strength, contractile properties, voluntary activation, and submaximal and maximal MUDRs of the TS muscles at two ankle joint positions: 20° dorsiflexed (DF; lengthened) and 20° plantar flexed (PF; shortened). Given the previously reported decrease in MG and LG MUDRs in a shortened position (Hali et al, 2019;Kennedy & Cresswell, 2001), we hypothesized that MG, LG, and soleus MUDRs will be higher in the DF (lengthened) compared with the PF (shortened) position.…”

Section: Introductionmentioning

confidence: 99%

“…However, in the hamstrings, maximal MUDRs were higher in the shortened compared with the lengthened position (Kirk & Rice, 2017). Furthermore, increases, decreases and no changes have been reported when comparing submaximal MUDRs at different muscle lengths (Bigland‐Ritchie et al, 1992; Christova et al, 1998; Del Valle et al 2004; Hali et al, 2019; Kennedy & Cresswell, 2001; Kirk & Rice, 2017; Lauber et al, 2014; Pasquet et al, 2005; Vander Linden et al, 1991).…”

Section: Introductionmentioning

confidence: 99%

“…Previous work has focused on the effect of changes in the knee joint angle to TS neuromuscular properties. In these studies, the gastrocnemii have demonstrated decreased submaximal MUDRs and increased motor unit recruitment thresholds when placed in a shortened position by flexing the knee joint (Hali et al, 2019; Kennedy & Cresswell, 2001). From surface electromyography (sEMG) recordings, it has been shown that when the knee joint is flexed, there was an increase in soleus activity to compensate for the compromised torque producing capability of the gastrocnemii in this position, despite no length change in the soleus (Kennedy & Cresswell, 2001).…”

Section: Introductionmentioning

confidence: 99%

“…From surface electromyography (sEMG) recordings, it has been shown that when the knee joint is flexed, there was an increase in soleus activity to compensate for the compromised torque producing capability of the gastrocnemii in this position, despite no length change in the soleus (Kennedy & Cresswell, 2001). However, no changes in soleus MUDRs or motor unit recruitment thresholds were found during plantar flexion contractions in a flexed compared with an extended knee joint position (Hali et al, 2019). Thus, it remains unclear how a change in ankle joint position, which affects the length of all components of the TS (MG, LG, and soleus) affects the neuromuscular properties of this muscle group.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, it has been reported that the components of the TS demonstrate different activation patterns during voluntary plantar flexion contractions with the soleus being recruited first, followed by the MG and then the LG (Hali et al, 2019; Héroux et al, 2014). The soleus is composed of ~85% slow‐twitch muscle fibers, whereas the gastrocnemii are composed of ~50% slow‐twitch muscle fibers (Johnson et al, 1973).…”

Section: Introductionmentioning

confidence: 99%

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Effect of ankle joint position on triceps surae contractile properties and motor unit discharge rates

2020

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The triceps surae (TS) length–tension relationship can be altered by changing the knee joint position, ankle joint position or both. However, studies exploring the effect of muscle length on neuromuscular properties have focused only on knee joint position changes affecting two of the three muscle components of the TS. Thus, the purpose of this study is to compare the neuromuscular properties of the three TS muscles during plantar flexion contractions at two ankle joint positions, 20° dorsiflexed (DF) and 20° plantar flexed (PF). Maximal isometric voluntary strength (MVC), voluntary activation, and evoked contractile properties of the ankle plantar flexors were compared between both ankle joint positions. Additionally, soleus, medial (MG), and lateral (LG) gastrocnemii motor unit discharge rates (MUDRs) were sampled during plantar flexion contractions at 25%, 50%, 75%, and 100% MVC using indwelling tungsten electrodes. MVC and peak twitch torque were lower by ~61% and 70%, respectively, whereas the maximal rate of torque relaxation was 39% faster in the PF compared with the DF position. Voluntary activation (~95%) was unaffected by changes in ankle joint position. LG MUDRs showed no differences between ankle joint positions, regardless of contraction intensity. Submaximal MG and soleus MUDRs showed no differences between the two ankle joint positions, however both muscles had 9% and 20% higher MUDRs in the DF position, respectively. These results provide further evidence for the differential activation among the three components of the TS with the greatest increases in soleus MUDRs compared with the gastrocnemii when the muscles are lengthened.

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Section: Introductionmentioning

confidence: 99%