Further research is needed to explore the analgesic effects of post-acute and chronic exercise and if effects are partially dependent on lower H-reflex/V-wave inhibition by group III and IV muscle afferents desensitization. In addition, it is important to note that the available research examining the interaction between exercise (acute and chronic) and pain did not compare the effect of different exercise modalities. Moreover, since discharge rate of III and IV afferents is highly dependent on specific task-metabolic requirements, it is relevant to determine if exercise modality differentially modulates the possible analgesic response via metaboreflex desensitization. Therefore, with this project, the investigators aim at exploring the influence of experimentally induced metaboreflex activation (group III and IV afferents) (maintained submaximal isometric contraction followed by blood-flow occlusion - post-exercise circulatory occlusion (PECO)) Vs. a control condition (no isometric contraction nor blood flow occlusion), on H-reflex recruitment curve and V-wave excitability (aim #1). Since the activation of group III/IV afferents can inhibit the corticospinal pathway, the investigators hypothesize that the normalized maximal amplitude of H- and V-wave and the slope of the ascending limb of the H-recruitment curve will decrease with metaboreflex activation (during PECO). Additionally, the investigators intend to examine the acute impact of different lower-limb exercise regimens (aerobic, anaerobic and dynamic resistance) on pain sensitivity (by the application of a foot cold pain tolerance test, by determining pressure pain threshold of exercising and non-exercising muscles and through self-reported leg ischemic pain ratings (0-10 Cook scale) - during PECO) (aim #2). Participants are also asked to mark the intensity of cold pain sensation using a visual analogue scale (VAS) with a horizontal line of 100mm, every 30 s of testing.This will allow the investigators to investigate the analgesic role of different acute exercise paradigms through possible metaboreflex desensitization given by altered neuromuscular responses at post-exercise time point (attenuated inhibition of H-reflex and V-wave amplitude during PECO). Also, once past research has shown that muscle metaboreflex activation reduces the sensitivity of the baroreflex, the investigators will measure arterial pressure (AP) and heart rate variability (HRV) during cold test and AP during ischemic testing. Despite all exercise modalities could enhance reducing pain sensibility after exercise, the investigators hypothesize that resistance and anaerobic exercise stimuli will enhance pain threshold/tolerance and reduced pain ratings via metaboreflex desensitization compared to that seen with endurance exercise (attenuated increase of AP and sympathetic component of HRV during cold pressor test and attenuated increase of AP during ischemic pain test). Finally, the investigators intend to explore the impact of long-term aerobic, anaerobic and resistance training on pain sensibility, using the same tests of aim #2 (aim #3). The investigators hypothesize that chronic EIH will be of greater magnitude after anaerobic and resistance exercise training vs. endurance training. This will be related with attenuated inhibition of H-reflex and V-wave amplitude measured during PECO and attenuated increase of AP and sympathetic component of HRV during metaboreflex activation after those training modalities. Nevertheless, the investigators expect to see an increased motor performance in all training regimens via heightened H-reflex (aerobic and anaerobic groups) and V-wave (resistance group) excitability.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
48
Aim #1 follows a randomized and crossover design in which 16 young and healthy males are evaluated during thigh circulatory occlusion performed after a submaximal isometric plantar flexion contraction (PECO day). In the other session, participants are evaluated during free-flow conditions and without previous fatiguing contraction (no-PECO day). In PECO day, participants complete a 3-min contraction at 40% of maximal force. Then, for testing, blood flow from lower-leg is blocked during 4 min, by an inflatable cuff around the ipsilateral thigh before task termination, during which H- reflex is tested. At the end of recordings, the cuff is deflated. Participants ware allowed to rest for 5-10 min. Then, they are requested to perform a new 3 min contraction with the cuff being inflated before task termination. The cuff remains inflated for \~ 2 min during which V-wave recordings are obtained. In both days, leg pain intensity is reported by participants and brachial AP is measured.
Aim #2 follows a randomized and crossover-controlled design, consisting on two experimental sessions. 24 healthy male (all diferent from Experiment 1) are randomly allocated to one of the following exercising regimens: aerobic, anaerobic or dynamic resistance (8 participants for each exercise group). In one of the experimental days, participants are evaluated for pain sensitivity and neuromuscular responses both before and after a lower-limb acute exercise protocol (exercise day) and in the other day before and after 15 min of quiet rest (non-exercise day). In both sessions, participants are evaluated for rectus femoris, upper trapezius and biceps brachiis muscles pressure pain threshold, followed by the application of a cold pain tolerance test on the foot. The intensity of pain is reported by a 0-100mm VAS and AP and HRV continously measured. Then, participants are tested for H-reflex and V-wave excitability during PECO, with leg pain intensity (0-10) and brachial AP recorded.
Aim #3 follows a randomized-controlled design. 32 healthy male (all the 24 participants from Experimental 2 plus 8 new subjects) are randomly allocated to one of the following groups: aerobic, anaerobic, dynamic resistance training and no-training (control) (8 participants for each group). Each intervention group perform 6 weeks of exercise training (3x week). Participants allocated to each training group are evaluated before and after training (2 assessment days in each time-point). On one day participants are tested for pressure pain threshold and cold pain tolerance with concomitant measures of pain ratings (0-100mm VAS), AP and HRV. The influence of metaboreflex activation on H-reflex and V-wave is also measured (during PECO). In addition, during PECO ischemic pain rating and AP are obtained. On another day, participants are evaluated for motor performance (maximal oxygen uptake, maximal voluntary contraction and peak power) and neuromuscular adaptations (i.e. H-reflex and V-wave)
Faculdade de Motricidade Humana
Lisbon, Portugal
H-reflex
With soleus electromyographic recording electrode (Delsys) and electrical stimulation of the tibial nerve (Stimsola) the H-reflex recruitment curve parameters (spinal excitability) will be obtained in a 4-min protocol
Time frame: During PECO and No-PECO conditions (aim #1); Pre-post acute exercise during PECO (aim #2); Pre-post 6 weeks of training during PECO (aim #3)
V-wave
With soleus electromyographic recording electrode (Delsys) and electrical stimulation of the tibial nerve (Stimsola) the V-wave parameters (spinal and supraspinal excitability) will be obtained
Time frame: During PECO and No-PECO conditions (aim #1); Pre-post acute exercise during PECO (aim #2); Pre-post 6 weeks of training during PECO (aim #3)
Ischemic pain ratings
Participants will be asked to rate their leg pain intensity twice at the 4-min H-reflex protocol (at 2nd and 4th min of the procedure) using a Cook pain sale (0-10). In the scale, 0 represents no pain while 10 represents the worst possible pain
Time frame: During PECO and No-PECO conditions (aim #1); Pre-post acute exercise during PECO (aim #2); Pre-post 6 weeks of training during PECO (aim #3)
Arterial blood pressure
Brachial arterial pressure will be measured twice at the 4-min H-reflex protocol (at 2nd and 4th min of the procedure) by an automated equiment (Tango SunTech Medical)
Time frame: During PECO and No-PECO conditions (aim #1); Pre-post acute exercise during PECO (aim #2); Pre-post 6 weeks of training during PECO (aim #3)
Pressure pain threshold
It will be assessed with an analogue algometer (FDK 60, Wagner Instruments) (in rectus femoris, upper-trapezius and biceps brachiis muscles). It measures the kg of force at the time participants report they are feeling pain intead of pressure
Time frame: Pre-post acute exercise (aim #2); Pre-post 6 weeks of training (aim #3)
Cold pain tolerance
It will be assessed with participants immersing their right foot into a container with cold water between 0 and 2ºC. It measures the time participants can endure the cold painful stimuli
Time frame: Pre-post acute exercise (aim #2); Pre-post 6 weeks of training (aim #3)
Cold pain ratings
While participants immerse their right foot into a container with cold water between 0 and 2ºC, they will beasked to rate the intensity of pain they perceived each minute by writing in a visual analogue scale (0-100mm) that pain intensity. 0 is considered no-pain and 100 the worst possible pain
Time frame: Pre-post acute exercise (aim #2); Pre-post 6 weeks of training (aim #3)
Heart rate variability during cold pain testing
It will be measured continuosly during the time participants have their foot in cold water using a heart rate monitor (Polar H10)
Time frame: Pre-post acute exercise (aim #2); Pre-post 6 weeks of training (aim #3)
Arterial blood pressure during cold pain testing
It will be measured each minute during the time participants have their foot in cold water using an automatic equipment (Tango SunTech Medical)
Time frame: Pre-post acute exercise (aim #2); Pre-post 6 weeks of training (aim #3)
Maximal oxygen uptake
For the aerobic group, it will be determined in a treadmill graded exercise testing using a gas analyses system (Metamax, Cortex)
Time frame: Pre-post 6 weeks of training (aim #3)
Peak power
For the anaerobic group, it will be determined with a 30-s Wingate all-out test (Monark cycloergometer)
Time frame: Pre-post 6 weeks of training (aim #3)
Maximal voluntary isometric contraction
For the dynamic resistance group, it will be determined for the knee extensors muscles using an isokinetic dynamometer (Biodex)
Time frame: Pre-post 6 weeks of training (aim #3)
H-reflex after training
With soleus electromyographic recording electrode (Delsys) and electrical stimulation of the tibial nerve (Stimsola) the H-reflex recruitment curve parameters (spinal excitability) will be obtained
Time frame: Pre-post 6 weeks of training (aim #3)
V-wave after training
With soleus electromyographic recording electrode (Delsys) and electrical stimulation of the tibial nerve (Stimsola) the V-wave parameters (spinal and supraspinal excitability) will be obtained
Time frame: Pre-post 6 weeks of training (aim #3)
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