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1

The influance of endurance, strength, and vibration training on sag in unfused tetanic contractions of fast motor units

100%
Krysciak K., Drzymala-Celichowska H., Smith I. C., Celichowski J.
Acta Neurobiologiae Experimentalis
|
2019
|
tom 79
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nr Suppl.1
INTRODUCTION: Unfused tetanic contractions of fast motor units exhibit a transitional decline in force following the initial extra-efficient force development, known as sag. Sag is sensitive to changing energy demands and the fuels metabolized to meet these demands. AIM(S): Since different training modes have varying effects on cellular energy systems in muscles, we aimed to determine how endurance, strength, and vibration training would affect sag in fast motor units of rat medial gastrocnemius. METHOD(S): Separate control groups were used for each training mode, with activity limited to normal cage movements. Endurance training (ET): 2, 4, or 8 weeks of treadmill training with weekly progressions in duration and speed. Strength training (ST): 5 weeks of voluntary progressive weight‑lifting. Vibration training (VT): 3 or 6 months of whole‑body vibration training at 50 Hz (4 × 30 s with 60 s rest periods). ET, ST, and VT groups were trained 5 days per week. Following training, functionally isolated fast motor units (divided into fast fatigable (FF) and fast fatigue-resistant (FR)) were investigated, and profiles of their unfused tetanic contractions at 40 Hz with sag were analyzed. RESULTS: The 40 Hz contractions of trained groups were less fused than those of untrained groups; this effect was attributable to shorter twitch time parameters in trained animals. Accordingly, numerous differences appeared in the sag profiles. However, when limiting the comparisons to motor units with comparable levels of fusion (fusion index 0.2 – 0.8), few differences were observed. With this constraint 1) ET had no effect on sag profiles, 2) the force decreased after the initial peak was delayed in FF of ST rats, and 3) VT resulted in a shorter duration of sag in FF and a smaller force decrease after the initial peak in FR. CONCLUSIONS: We conclude that while different training modes have differing effects on sag, these effects are primarily due to altered twitch time parameters.
2

Changes in the contractile properties of motor units in functionally overloaded medial gastrocnemius muscle of the rat

100%
Krysciak K., Drzymala-Celichowska H., Krutki P., Celichowski J.
Acta Neurobiologiae Experimentalis
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2011
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tom 71
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nr S
The study aimed at examining the contractile properties of motor units (MUs) in medial gastrocnemius muscle subjected to 3 months compensatory overload, induced by bilateral tenotomy of its synergists (lateral gastrocnemius, plantaris and soleus). To assure that operated muscles were regularly voluntarily activated, surgical procedures were followed by keeping animals in wheelequipped cages and treadmill exercise. The final electrophysiological experiments were carried out on 106 MUs of the overloaded medial gastrocnemius muscle (OMG) and 88 MUs of the untreated, healthy gastrocnemius muscle (MG). Functionally isolated MUs were examined by electrical stimulation of thin filaments of the L4 – L5 ventral roots. MUs classification was based on 20 Hz tetanus index which divided MUs into fast and slow, whereas the fatigue index distinguished fast fatigable (FF) and fast resistant (FR) MUs. Results showed that both OMG mass and its relation to the body weight were higher in comparison to MG. MUs proportion was modified in response to altered functional demand and in OMG higher percentage of S and FF simultaneously with lower contribution of FR MUs were observed. Changes in MUs contractile properties of OMG in comparison to MG included: shorter half-relaxation time and lower twitch force in all types of MUs and in parallel higher (FR and S) or unchanged (FF) tetanus force. Changes in force parameters in OMG resulted in lower values of the twitch-to-tetanus ratio in all three types of MUs. Higher posttetanic potentiation was also noted for all MUs types in OMG. Changes in fatigue resistance were observed only in fast MUs: for FF type the mean value of the fatigue index was lower in OMG in comparison to MG, but for FR type this value was higher in OMG. In conclusion, the adaptation of the medial gastrocnemius muscle to overload included transformation of some MUs accompanied by changes in MUs contractile properties.
3

The motor unit contractile properties of rat medial gastrocnemius muscle subjected to three months compensatory overload

100%
Krysciak K., Drzymala-Celichowska H., Krutki P., Celichowski J.
Acta Neurobiologiae Experimentalis
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2013
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tom 73
|
nr Suppl.1
Compensatory overload of medial gastrocnemius muscle was induced by bilateral tenotomy of synergists (lateral gastrocnemius, plantaris and soleus). Operated muscles were regularly voluntarily activated as after surgery rats were kept in wheel-equipped cages and additionally were exercised on a treadmill. 3 months after the surgery the final electrophysiological experiments were carried out. 106 motor units (MUs) of the overloaded muscle (OMG) and 154 MUs of the untreated muscle (MG) were studied. Results showed that OMG mass and its relation to the body mass were higher in comparison to MG. In OMG higher percentage of slow (S) and fast fatigable (FF) MUs and lower contribution of fast resistant (FR) MUs as compared to MG were noted. Changes in MUs contractile properties of OMG included: lower twitch force and higher tetanus force (resulted in lower values of the twitch-to-tetanus ratio), higher post-tetanic potentiation in all MUs types and shorter halfrelaxation time for S MUs. Changes in fatigue resistance concerned FF and S MUs: in OMG the fatigue index for FF was lower, but for S higher as compared to MG. In conclusion, the 3-month period of the muscle overload induced changes in MUs contractile properties accompanied by transformational processes.
4

The transitory force decrease following high-frequency stimulation burst in unfused tetani of motor units

100%
Grzesiak J., Krysciak K., Drzymala-Celichowska H., Celichowski J.
Acta Neurobiologiae Experimentalis
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2017
|
tom 77
|
nr Suppl.1
INTRODUCTION: The changes in force of motor units (MUs) following changes in activation pattern still are not fully understood, especially in relation to effects of decreasing rate of stimuli. It is known that at linearly decreasing stimulation frequency the force decrease is slower than expected when comparing to the constant stimulation frequency. AIM(S): The aim of study was the explanation of recently observed surprising transitory force decrease resulting from a sudden decrease in stimulation frequency. METHOD(S): The research was conducted on 6 adult female Wistar rats under pentobarbital anesthesia. 24 slow (S), 38 fast fatigable (FF) and 65 fast resistant (FR) MUs were isolated. Studied MUs were stimulated with several trains of stimuli composed of three phases: first, 500 ms at low frequency, second, 300 ms at high frequency and third, 500 ms at the same low frequency. The tested low frequencies for fast MUs were 10, 20, 30, 40 and 50 Hz, and high frequencies amounted to 75, 90 and 150 Hz, whereas for slow motor units low frequencies were 10, 12.5, 15, 17.5, 20 and 25 Hz and high frequencies amounted to 50 and 75 Hz. Moreover, these trains of stimuli were tested at different levels of muscles stretching (30 mN, 100 mN, 200 mN) for all types of MUs. RESULTS: Among the three MU types the studied force decrease was most frequent and the strongest for FR MUs. The highest noted decrease amounted to 36.5%. The greatest transitory force decreases were observed at muscle passive stretch of 100 mN. For MUs of the three types the force decrease was observed at middle-fused tetanic contractions (the fusion index 0.30–0.95). CONCLUSIONS: The phenomenon most probably has biomechanical background and is conditioned by distribution of contracting muscle fibers in a deep part of muscle and slow adaptation of stretched collagen fibers to the lower force level of contracting muscle fibers at reduced stimulation frequency. FINANCIAL SUPPORT: National Science Centre, Poland.
5

The influence of 12 weeks high fat diet and low dose streptozotocin-induced diabetes on contractile properties of motor units in medial gastrocnemius muscle of rat

88%
Krysciak K., Drzymala-Celichowska H., Krutki P., Lochyński D., Celichowski J.
Acta Neurobiologiae Experimentalis
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2017
|
tom 77
|
nr Suppl.1
INTRODUCTION: Obesity and diabetes, with associated conditions termed as metabolic syndrome are growing problem worldwide. Consequences of impaired glucose metabolism affect the whole organism including neuromuscular system. Diabetic neuropathy influences predominantly sensory system and to smaller degree motor system. Additionally, skeletal muscles as involved in glucose metabolism are exposed to processes related to insulin resistance. AIM(S): The study was aimed to investigate effects of high fat diet and streptozotocin-induced diabetes on motor unit’s (MUs) contractile properties in rat medial gastrocnemius (MG) muscle. METHOD(S): Male rats weighting about 180 g were randomly assigned to 3 groups: C, untreated, control, on standard laboratory diet (n=10); HFD, on high fat diet for 12 weeks (n=10); and STZ, on high fat diet for 8 weeks, then injected with a single dose of STZ – 35 mg/kg (n=13). Contractile properties of MUs were investigated in electrophysiological experiments. RESULTS: Both interventions increased the glucose level in the blood but evoked no changes in MG mass. Proportions of the 3 MUs types (FF; fast fatigable, FR; fast resistant and S; slow) were not changed neither in HFD nor STZ compared to C but contractile properties differed significantly in HFD and/or STZ in relation to C. For both fast MU types the twitch time parameters in HFD and STZ were longer, and the twitch-to-tetanus ratio was higher in STZ. The force frequency curves were shifted to lower frequencies in HFD and STZ compared do C, and their slope increased in HFD compared to C group. Furthermore, for FR MUs the force potentiation was lower in STZ compared to C. For S MUs higher tetanus force in HFD compared to C was noted. CONCLUSIONS: Although high fat diet and low dose of streptozotocin have not changed the MG mass and MU proportions, the impaired glucose metabolism modified force-regulation mechanisms of fast MUs in studied muscle.
6

Factors contributing to sag in unfused tetanic contractions of fast motor units in rat

88%
Celichowski J., Krysciak K., Raikova R., Krutki P., Drzymala-Celichowska H.
Acta Neurobiologiae Experimentalis
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2017
|
tom 77
|
nr Suppl.1
7

Division of motor units into fast and slow on the basis of profile of 2O Hz unfused tetanus

88%
Krysciak K., Krutki P., Celichowski J., Slawinska U., Maiczynski H.
Acta Neurobiologiae Experimentalis
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2007
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tom 67
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nr 3
8

Sinusoidal mechanical responses from single motor units of rat medial gastrocnemius muscle

76%
Drzymala-Celichowska H., Krysciak K., Kaczmarek P., Orizio C., Krutki P., Celichowski J.
Acta Neurobiologiae Experimentalis
|
2017
|
tom 77
|
nr Suppl.1
INTRODUCTION: The relationship between the output force and motor command depends on the intrinsic RESULTS: The mathematical decomposition of unfused tetanic contractions of FF and FR MUs into twitch-shape responses to consecutive stimuli was conducted. The decomposition indicated substantial changes predominantly in force and additionally in time parameters of successive twitch‑like components, responsible for a sag profile in tetanic curve. Namely, initially the force increased and the highest force was observed in a response to the 2nd–3rd stimulus for FF units, while after the 3rd–7th stimulus for FR MUs and later decreased leading to the sag. In the second series of experiments, a repeatability of the sag in tetanic contractions of the same MU in a muscle with preserved blood circulation and under ischemic conditions was tested. Sag restitution was present in muscles with the circulation preserved but it was prevented by occlusion of blood vessels, indicating that sag depends on an availability of an energy source which can be restituted under aerobic conditions. CONCLUSIONS: The study indicated that sag profile of unfused tetanic contractions is predominantly an effect of early increase in amplitudes of several initial responses followed by a decrease in their amplitudes and that these changes are stronger and longer in time scale in FR than in FF MUs. The results concerning repeatability of the phenomenon suggest that most probable source of energy for initial force increase is phosphocreatine.
9

Adaptive changes in motor unit contractile properties to endurance training

76%
Krysciak K., Krysciak J., Lochynski D., Kaczmarek D., Drzymala-Celichowska H., Krutki P., Celichowski J.
Acta Neurobiologiae Experimentalis
|
2015
|
tom 75
|
nr Supl.
BACKGROUND AND AIMS: Endurance training is based on a repeated, prolonged activation of a large number of muscles. It causes morphological, biochemical and metabolic changes in the muscles and the nervous system. However, there are no data concerning changes in motor unit (MU) contractile properties following endurance training. METHODS: 61 male rats were assigned to 4 groups, untrained – control (C), and 3 groups trained on a treadmill, 5 days a week for 2 weeks (2W), 4 weeks (4W) or 8 weeks (8W). The special protocol determined duration and speed of locomotion in the consecutive days of the training. Finally, rats of the 2W group covered average distance of 5.5 km, 4W of 21 km, and 8W of 56 km. Afterwards, functionally isolated MUs of the medial gastrocnemius muscle were electrophysiologically investigated. RESULTS: The mean body mass of rats of all trained groups was lower in comparison to the C group, but no differences between 2W, 4W and 8W groups were noted. The muscle mass and the muscle-to-body mass ratio were not different between groups. The proportion of fast resistant (FR) MUs was higher, while of fast fatigable (FF) lower in all trained groups, in comparison to the C group. The relative number of slow (S) MUs increased only in the 8W group. MU contractile properties were changed mainly in FR MUs and included: lower contraction and half-relaxation times, lower twitch forces, higher tetanus forces and lower twitch-to-tetanus ratio. Few adaptive changes were noted also for S MUs of trained animals: lower twitch and tetanus forces as well as lower twitch-to-tetanus ratio. For FR and S MUs of all trained groups the force decrease within four minutes of the fatigue test was considerably slower or even completely abolished, which was reflected in the increased fatigue indexes. CONCLUSION: The main adaptive changes appeared early and then slowly increased within the endurance training. Supported by the National Science Center grant 2013/09/B/ NZ7/02555.
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