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Responders to Wide-Pulse, High-Frequency Neuromuscular Electrical Stimulation Show Reduced Metabolic Demand: A 31P-MRS Study in Humans.

Wegrzyk J, Fouré A, Le Fur Y, Maffiuletti NA, Vilmen C, Guye M, Mattei JP, Place N, Bendahan D, Gondin J - PLoS ONE (2015)

Bottom Line: Furthermore, a fatigue index based on FTI loss at the end of each protocol compared with the beginning of the protocol was calculated.Only for the responder group, the ∆PCr/FTI ratio of WPHF (0.74 ± 0.19 M/N.s) was significantly lower compared to CONV (1.48 ± 0.46 M/N.s) but similar to VOL (0.65 ± 0.21 M/N.s).Moreover, the fatigue index was not different between WPHF (-16%) and CONV (-25%) for the responders.

View Article: PubMed Central - PubMed

Affiliation: Aix-Marseille Université, CNRS, CRMBM UMR 7339, Marseille, France.

ABSTRACT
Conventional (CONV) neuromuscular electrical stimulation (NMES) (i.e., short pulse duration, low frequencies) induces a higher energetic response as compared to voluntary contractions (VOL). In contrast, wide-pulse, high-frequency (WPHF) NMES might elicit--at least in some subjects (i.e., responders)--a different motor unit recruitment compared to CONV that resembles the physiological muscle activation pattern of VOL. We therefore hypothesized that for these responder subjects, the metabolic demand of WPHF would be lower than CONV and comparable to VOL. 18 healthy subjects performed isometric plantar flexions at 10% of their maximal voluntary contraction force for CONV (25 Hz, 0.05 ms), WPHF (100 Hz, 1 ms) and VOL protocols. For each protocol, force time integral (FTI) was quantified and subjects were classified as responders and non-responders to WPHF based on k-means clustering analysis. Furthermore, a fatigue index based on FTI loss at the end of each protocol compared with the beginning of the protocol was calculated. Phosphocreatine depletion (ΔPCr) was assessed using 31P magnetic resonance spectroscopy. Responders developed four times higher FTI's during WPHF (99 ± 37 × 10(3) N.s) than non-responders (26 ± 12 × 10(3) N.s). For both responders and non-responders, CONV was metabolically more demanding than VOL when ΔPCr was expressed relative to the FTI. Only for the responder group, the ∆PCr/FTI ratio of WPHF (0.74 ± 0.19 M/N.s) was significantly lower compared to CONV (1.48 ± 0.46 M/N.s) but similar to VOL (0.65 ± 0.21 M/N.s). Moreover, the fatigue index was not different between WPHF (-16%) and CONV (-25%) for the responders. WPHF could therefore be considered as the less demanding NMES modality--at least in this subgroup of subjects--by possibly exhibiting a muscle activation pattern similar to VOL contractions.

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Summation of the first spectra for four subsequent trains in order to improve spectral resolution and to assess PCr depletion over time (i.e. five time-points, i.e., contraction C4; C8; C12; C16; C20).Each rectangle represents one contraction of 20 seconds, each arrow one MR spectrum acquired from 2 sec after each contraction.
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pone.0143972.g001: Summation of the first spectra for four subsequent trains in order to improve spectral resolution and to assess PCr depletion over time (i.e. five time-points, i.e., contraction C4; C8; C12; C16; C20).Each rectangle represents one contraction of 20 seconds, each arrow one MR spectrum acquired from 2 sec after each contraction.

Mentions: Due to stimulation artifacts during the NMES-induced contractions, the spectra for each protocol were only analyzed during the resting intervals of the 20 contractions. In order to obtain an adequate spectral resolution for the phosphorylated compounds and to avoid metabolic changes due to recovery, only the first spectrum immediately after each contraction was considered. All these spectra were then averaged for four contractions each (Fig 1). This analysis allowed to monitor the kinetics of the metabolic changes during each protocol.


Responders to Wide-Pulse, High-Frequency Neuromuscular Electrical Stimulation Show Reduced Metabolic Demand: A 31P-MRS Study in Humans.

Wegrzyk J, Fouré A, Le Fur Y, Maffiuletti NA, Vilmen C, Guye M, Mattei JP, Place N, Bendahan D, Gondin J - PLoS ONE (2015)

Summation of the first spectra for four subsequent trains in order to improve spectral resolution and to assess PCr depletion over time (i.e. five time-points, i.e., contraction C4; C8; C12; C16; C20).Each rectangle represents one contraction of 20 seconds, each arrow one MR spectrum acquired from 2 sec after each contraction.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4664273&req=5

pone.0143972.g001: Summation of the first spectra for four subsequent trains in order to improve spectral resolution and to assess PCr depletion over time (i.e. five time-points, i.e., contraction C4; C8; C12; C16; C20).Each rectangle represents one contraction of 20 seconds, each arrow one MR spectrum acquired from 2 sec after each contraction.
Mentions: Due to stimulation artifacts during the NMES-induced contractions, the spectra for each protocol were only analyzed during the resting intervals of the 20 contractions. In order to obtain an adequate spectral resolution for the phosphorylated compounds and to avoid metabolic changes due to recovery, only the first spectrum immediately after each contraction was considered. All these spectra were then averaged for four contractions each (Fig 1). This analysis allowed to monitor the kinetics of the metabolic changes during each protocol.

Bottom Line: Furthermore, a fatigue index based on FTI loss at the end of each protocol compared with the beginning of the protocol was calculated.Only for the responder group, the ∆PCr/FTI ratio of WPHF (0.74 ± 0.19 M/N.s) was significantly lower compared to CONV (1.48 ± 0.46 M/N.s) but similar to VOL (0.65 ± 0.21 M/N.s).Moreover, the fatigue index was not different between WPHF (-16%) and CONV (-25%) for the responders.

View Article: PubMed Central - PubMed

Affiliation: Aix-Marseille Université, CNRS, CRMBM UMR 7339, Marseille, France.

ABSTRACT
Conventional (CONV) neuromuscular electrical stimulation (NMES) (i.e., short pulse duration, low frequencies) induces a higher energetic response as compared to voluntary contractions (VOL). In contrast, wide-pulse, high-frequency (WPHF) NMES might elicit--at least in some subjects (i.e., responders)--a different motor unit recruitment compared to CONV that resembles the physiological muscle activation pattern of VOL. We therefore hypothesized that for these responder subjects, the metabolic demand of WPHF would be lower than CONV and comparable to VOL. 18 healthy subjects performed isometric plantar flexions at 10% of their maximal voluntary contraction force for CONV (25 Hz, 0.05 ms), WPHF (100 Hz, 1 ms) and VOL protocols. For each protocol, force time integral (FTI) was quantified and subjects were classified as responders and non-responders to WPHF based on k-means clustering analysis. Furthermore, a fatigue index based on FTI loss at the end of each protocol compared with the beginning of the protocol was calculated. Phosphocreatine depletion (ΔPCr) was assessed using 31P magnetic resonance spectroscopy. Responders developed four times higher FTI's during WPHF (99 ± 37 × 10(3) N.s) than non-responders (26 ± 12 × 10(3) N.s). For both responders and non-responders, CONV was metabolically more demanding than VOL when ΔPCr was expressed relative to the FTI. Only for the responder group, the ∆PCr/FTI ratio of WPHF (0.74 ± 0.19 M/N.s) was significantly lower compared to CONV (1.48 ± 0.46 M/N.s) but similar to VOL (0.65 ± 0.21 M/N.s). Moreover, the fatigue index was not different between WPHF (-16%) and CONV (-25%) for the responders. WPHF could therefore be considered as the less demanding NMES modality--at least in this subgroup of subjects--by possibly exhibiting a muscle activation pattern similar to VOL contractions.

Show MeSH
Related in: MedlinePlus