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SpillOver stimulation: A novel hypertrophy model using co-contraction of the plantar-flexors to load the tibial anterior muscle in rats.

ABSTRACT: The influence of loading on muscular hypertrophy has previously been studied in rodents by removal of synergistic muscles or various weight-lifting regimes. We present a novel model, evoking hypertrophy in the rat's tibialis anterior (TA) muscle by means of an implanted single channel electrical nerve stimulator. The amount of load experienced by the TA was measured in acute experiments in anaesthetized rats with contractions over a range of stimulation frequency and amplitude. A novel electrode configuration allowed us to elicit concentric, isometric and eccentric contractions within the same setup. This was achieved by 'SpillOver' stimulation in which we adjusted the amount of co-activation of the stronger antagonistic plantarflexors by increasing the stimulus above the level that caused full recruitment of the dorsiflexor muscles. The effect of loading on hypertrophy of the TA was tested in 3-4 week stimulation experiments in two groups of freely-moving rats, with a protocol that resembles typical resistance-training in humans. One group performed concentric contractions with no antagonistic co-contraction (unloaded, UNL, n = 5). In the other group the TA was loaded by simultaneous co-contraction of the antagonistically acting plantarflexors (SpillOver, n = 5). The wet mass of the stimulated TA increased in both groups; by 5.4 ± 5.5% for the UNL-group and 13.9 ± 2.9% for the SpillOver-group, with significantly greater increase in the SpillOver-group (p<0.05). Our results correlate well with values reported in literature, demonstrating that SpillOver-stimulation is a suitable model in which to study muscular hypertrophy. Even higher gains in muscle-mass may be possible by optimizing and adjusting the stimulation parameters according to the principles of progressive resistance training.

SUBMITTER: Schmoll M

PROVIDER: S-EPMC6245836 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Isometric muscle force attained during isometric contractions decreases after active shortening compared to that attained during purely isometric contractions. This phenomenon is called residual force depression. The aim of this study was to examine whether residual force depression occurs in human plantar flexors in both plantar flexed and dorsiflexed region. In addition, the magnitude of fascicle shortening was evaluated because not only muscle force but also fascicle shortening during active shortening are considered to affect force depression. Eleven male subjects were recruited. All muscle contractions were evoked by muscle belly-electrical stimulation. In the reference trials, isometric plantar flexion (PF) was performed at 0° and 15° of PF. In the residual force depression trials, the following two contractions were conducted: (1) muscles were activated isometrically at 15° of dorsiflexion, then actively shortened to 0° of PF (long condition) and (2) muscles were activated isometrically at 0° of PF, then actively shortened to 15° of PF (short condition). Isometric joint torque obtained 4.9 s after the onset of contraction was compared between the reference and residual force depression trials at the same joint angle to calculate the magnitude of residual force depression. At the same time point, fascicle length and pennation angle were obtained from ultrasonographic images to examine whether the muscle architecture affected residual force depression. As a result, residual force depression was confirmed in both the long and short length conditions (long: 87.1 ± 9.1%, short: 92.1 ± 7.8%) while the magnitude was not different (p = 0.182). The fascicle length and pennation angle were not different between the reference and residual force depression trials (p = 0.291-0.906). These results indicate that residual force depression occurs in the physiological range of motion in the human plantar flexors, and this phenomenon is not related to muscle architecture. In addition, joint angle dependence of the residual force depression was not observed between long and short muscle length conditions.

Project description:Compared to pure isometric contractions, isometric muscle force at a given length is larger when the eccentric contraction is conducted before the isometric contraction. This phenomenon is widely known as residual force enhancement, and has been confirmed consistently in isolated muscle experiments. The purpose of this study was to confirm whether residual force enhancement also occurs in human plantar flexors and to examine its joint angle dependence. Eleven men participated in this study. Isometric joint torque was measured in a Control trial (pure isometric contraction) and Residual force enhancement (RFE) trial (isometric contraction after eccentric contraction) at plantar flexion 0° (Short condition) and dorsiflexion 15° (Long condition). Fascicle length and pennation angle of the medial gastrocnemius were measured simultaneously to evaluate the influence of architectural parameters on isometric joint torque. Isometric joint torque observed in the Short condition was not significantly different between the Control and RFE trials (Control: 42.9 ± 8.0 Nm, RFE: 45.1 ± 8.4 Nm) (p = 0.200). In contrast, significant differences in isometric joint torque were observed in the Long condition between Control and RFE trials (Control: 40.5 ± 9.3 Nm, RFE: 47.1 ± 10.5 Nm) (p = 0.001). Fascicle length and pennation angle were not different between Control and RFE trials in the Short and Long conditions. Isometric joint torque was larger when eccentric contraction was conducted before isometric contraction while architectural differences were not observed, indicating that residual force enhancement occurs in human plantar flexors. However, the influence of residual force enhancement may be limited in dorsiflexed positions because the magnitude of residual force enhancement is considered to be prominent in the descending limb (long muscle length condition) and small in the ascending limb (short muscle length condition) where human plantar flexors operate in plantar flexed positions.

Project description:PurposeThe purpose of our pilot study was to assess the effect of augmenting anterior cruciate ligament (ACL) repair with suture tape on biomechanical parameters including anterior tibial translation, gap formation, and load to failure.MethodsTen fresh-frozen nonpaired cadaveric knees were dissected, and baseline anterior-posterior stability of both ACL-intact and -deficient knees was obtained. The specimens were randomized to undergo ACL repair either with or without suture tape reinforcement, and anterior tibial translation, as well as gap formation, was measured after cyclic loading. Finally, all specimens were subjected to a single pullout force to determine maximum load to failure. We performed t test analysis to compare means between groups, and significance was defined as P < .05.ResultsOn t test analysis, no statistically significant difference was found regarding anterior tibial translation between the ACL-intact group and either repair group or between the repair group without suture tape augmentation and the repair group with suture tape augmentation. No significant difference in gap formation was detected between the repair groups with and without suture tape augmentation at 100 cycles (1.25 mm vs 1.02 mm, P = .6), 250 cycles (2.87 mm vs 2.12 mm, P = .3), and 500 cycles (4.5 mm vs 4.55 mm, P = .5). The average load to failure of the repairs without suture tape augmentation was not significantly different from that of the repairs with suture tape augmentation (725.9 N vs 725.7 N, P = .99).ConclusionsIn this pilot study, we did not identify a difference between ACL repairs with and without suture tape augmentation regarding anterior tibial translation, gap formation, or maximum load to failure.Clinical relevanceTreatment of ACL tears with primary ACL repair is a highly debated topic, and studies such as this study to further our understanding of the biomechanical properties of augmented ACL repairs are important for surgeons when deciding the best treatments for their patients.

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SpillOver stimulation: A novel hypertrophy model using co-contraction of the plantar-flexors to load the tibial anterior muscle in rats.

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