Total Body and Extracellular Water Measures Are Unrelated to Cramp Sensitivity in Euhydrated Cramp-Prone Individuals

Earp, JE, Stearns, RL, Agostinucci, J, Lepley, AS, and Ward-Ritacco, CL. Total body and extracellular water measures are unrelated to cramp sensitivity in euhydrated cramp-prone individuals. J Strength Cond Res XX(X): 000-000, 2020-Spectral bioelectrical impedance analysis (BIA) is a valid and noninvasive tool for measuring total body water (TBW), intracellular water (ICW), and extracellular water (ECW). As altered hydration and electrolyte imbalance have been proposed as one of 2 etiologies for exercise-associated muscle cramps (EAMC), the purpose of this study was to determine if distribution of body water is related to cramp sensitivity in similarly hydrated cramp-prone individuals. To this end, 11 euhydrated subjects who regularly experience EAMC had their relative TBW, ICW, and ECW assessed using 8-pole spectral BIA. Subjects' cramp sensitivity was then assessed by electrically stimulating the tibial nerve at increasing frequencies until a muscle cramp occurred, allowing for the determination of the threshold frequency (TF) at which the cramp occurred. It was observed that TF was not significantly related to TBW (r = 0.087, p = 0.368), ICW (r = 0.105, p = 0.338), ECW (r = 0.087, p = 0.368), or ECW:TBW (r = 0.147, p = 0.280). As cramp etiology is poorly understood, these results add to a growing body of literature questioning the role of hydration and electrolyte imbalance in EAMC. Although fluid distribution may be unrelated to TF in those who commonly experience EAMC, additional research is needed to compare those who commonly experience cramps (athletes as well as individuals with specific neuropathies or pharmacologically induced cramps) with those who do not experience cramps and to determine if acute shifts in body water compartmentalization are related to changes in cramp sensitivity.

Electrolyte beverage consumption alters electrically induced cramping threshold

BACKGROUND

Recent investigations have questioned the role of hydration and electrolytes in cramp susceptibility and thus the efficacy of consuming electrolyte-rich carbohydrate beverages (EB) to control/prevent cramping.

METHODS

Nine euhydrated, cramp-prone participants had their cramp susceptibility assessed by measuring the nerve stimulation threshold frequency at which cramping occurs (TF) before and after consumption of an EB (kCal: 120, Na: 840 mg, K: 320 mg, Mg: 5 mg) and placebo beverage (PB: kCal: 5, Na: 35 mg). Cramp intensity was assessed using a verbal pain scale and poststimulation electromyography (EMG).

RESULTS

TF was greater in EB (14.86 ± 7.47 Hz) than PB (14.00 ± 5.03 Hz; P = .038) and reported pain was lower in EB (2.0 ± 0.6) than PB (2.7 ± 0.8; P = .025) while EMG was similar (P = .646).

DISCUSSION

EB consumption decreased cramp susceptibility and pain but did not prevent cramping in any participants. These results suggest that electrolyte consumption independent of hydration can influence cramp susceptibility in young people.

The effects of circumferential pressure on the soleus muscle F-wave in healthy subjects

Circumferential pressure (CP) was shown to decrease muscle activity in subjects without neuromuscular disorders and in individuals with spinal cord injury and cerebrovascular accidents. The mechanism for this decrease is unknown although it is hypothesized to be spinal in origin. The purpose of this study was to investigate the effect CP has on the soleus F-wave. Results will help determine the mechanism CP uses to effect motoneuron reflex excitability. Thirty-seven healthy volunteers participated. A 16cm air-splint was placed around the calf and during the pressure phase of the experiment it was inflated to 40-45mm Hg. F-waves were evoked by supra maximally stimulating (20%>Mmax) the tibial nerve with a 0.1ms pulse at 0.2Hz using a bipolar surface electrode on the skin of the popliteal fossa. Fifty F-waves were recorded before (baseline), during, and 3) after CP was applied. F-waves were then identified and mean latency, persistence, and mean F/Mmax amplitude ratios were measured and calculated. Friedman Repeated Measures on Ranks tests were conducted on each of the three parameters (p⩽0.05). No statistically significant difference was found for any of the F-wave parameters evaluated. These results were contrary to previous CP studies that observed a significant decrease in muscle activity. Possible reasons for this discrepancy are discussed.

Inhibitory effects of circumferential pressure on flexor carpi radialis H-reflex in adults with neurological deficits

The effects of circumferential air-splint pressure on the flexor carpi radialis H-reflex in 22 participants with cerebrovascular accident and 5 with spinal cord injury were examined. H-reflexes were assessed by measuring the peak-to-peak amplitude change before, during, and after circumferential pressure was applied to the forearm. 12 H-reflexes (H/M ratio: M = 25%; SD = 14) were recorded before pressure application to obtain a baseline value for comparison of data. A pneumatic 34-cm air splint inflated to 51-60 mmHg provided pressure around the forearm. H-reflex recordings were taken at 1, 3, and 5 min. during and 1 min. after application of pressure. A one-way analysis of variance with repeated measures was applied to compare pressure and postpressure measurements against the baseline value. Tukey multiple-comparison tests were used when significant F ratios were noted. Analysis indicated H-reflex amplitudes decreased significantly at 1, 3, and 5 min. during pressure and quickly returned to baseline when pressure was released. The study suggests air splints decreased the H-reflex in participants with neurological deficits and may be used in the upper extremity temporarily to reduce muscle activity associated with neurological dysfunction.

The effects of circumferential air-splint pressure on flexor carpi radialis H-reflex in subjects without neurological deficits

The purposes of this study were to investigate the effects of circumferential pressure on flexor carpi radialis (FCR) H-reflex in subjects without neuromuscular deficits and to evaluate the skin's contribution to this effect. FCR H-reflex was assessed in 43 subjects by measuring the peak-to-peak amplitude change before, during, and after circumferential pressure was applied to the forearm. Twelve H-reflexes (H/M ratio: M = 25%, SD = 14) were recorded before pressure application to obtain a baseline value (H(baseline)) to which all data were compared. A pneumatic 15 to 20-cm air splint inflated to 51-60 mmHg provided the pressure around the forearm. H-reflex recordings were taken at 1, 3, and 5 min. during (H(pressure)) and after pressure application. A second smaller study (placebo), in which the air splint was inflated to 0 mmHg, was conducted in 5 subjects to ensure that changes in reflex amplitudes were not a result of cutaneous effects. Two types of responses were observed in the FCR H-reflex following pressure application. One group of subjects significantly increased in H-reflex amplitude while another group decreased in H-reflex amplitude when compared to H(baseline). Regression analysis found that H(max) explained 37.2% of the variance when controlling for H(baseline). Subjects with larger H(max) showed an increase in H(pressure) while subjects with lower H(max) showed decreases in H(pressure) The placebo study revealed no differences in H-reflex amplitude from baseline values, implying that skin stimulation from the air splint has no role in the effects observed. The dichotomous result indicates that pressure influences the upper extremity differently than it does the lower extremity in certain individuals. Clinicians, using circumferential pressure as a therapeutic modality to lower muscle activity of the upper extremity, need to be cognizant that pressure may have contrasting effects on their patients.

Air-splint pressure effect on soleus muscle alpha motoneuron reflex excitability in subjects with spinal cord injury

OBJECTIVE

This study investigated circumferential pressure effect on soleus motoneuron reflex excitability in subjects with spinal cord injury (SCI).

SETTING

A university neuromuscular research laboratory.

SUBJECTS

Six men with SCI, clinical level above L1. OUTCOME MEASURES AND INTERVENTION: Soleus motoneuron reflex excitability was assessed by measuring the average change in the peak-to-peak amplitude of 10 H-reflexes before (baseline), during (1, 3, and 5min) and after (1, 3, and 5min) pressure application. Pressure was applied to the lower leg by manually inflating an air-splint to a maintained range of 36.7 to 40.8mmHg for 5 minutes, after which it was deflated.

DESIGN

Repeated measures, planned comparison. Dependent variables compared with baseline values only in post hoc tests.

RESULTS

A one-way analysis of variance for repeated measures demonstrated significant difference (F6,30 = 4.03; p = .004) in the H-reflex amplitude across test conditions. Post hoc t tests (with Bonferroni's correction for multiple comparisons, p < or = .008) revealed a significant H-reflex amplitude reduction at 1, 3, and 5 minutes of pressure application when measurements were compared with the baseline value. Postpressure measurements returned to baseline; however, the third minute measurement was significantly greater than baseline values.

CONCLUSIONS

Circumferential pressure applied to the lower leg decreased soleus muscle alpha motoneuron reflex excitability in subjects with SCI. This inhibition lasted only as long as the pressure was applied. Circumferential pressure application may be useful when a temporary decrease in muscle activity is a therapeutic goal in patients with SCI.

The effect of topical anesthetics on skin sensation and soleus motoneuron reflex excitability

The effect that topical anesthetics has on cutaneous sensation and on soleus motoneuron reflex excitability was studied in a healthy population. Data were obtained from 16 volunteers (7 men and 9 women) between 20 and 47 years of age. The experiment consisted or recording H-reflexes and Achilles tendon reflexes (ATR) before and after administration of a 20% benzocaine spray or a placebo to the skin of the posterior calf. In addition, a sensory evaluation was conducted to determine objectively the actual quality of anesthesia obtained. Subjects served as their own controls, randomly receiving both the active medication and a placebo. The study was conducted in a single blind fashion with only the experimenter being aware of what medication (active/placebo) was being applied during a given experiment. H-reflex amplitudes increased significantly following the application of benzocaine and the placebo spray compared to control (p < .01). This increase was similar whether the active drug or placebo was administered. No significant difference was shown between active benzocaine and the placebo application. The ATR was not significantly affected by any of the treatment techniques used in this study, although some reduction in reflex amplitude was noted. No change in skin sensibility could be attributed to the topical anesthetic in any subject in this study. It was concluded that benzocaine spray did not have an effect on skin sensation and that the increased motoneuron reflex excitability was more likely in response to a stimulatory action upon cutaneous receptors from the spray technique. It is further suggested that topical anesthetics applied to intact skin may not permeate cutaneous tissue in large enough quantities to have a desensitizing effect.

Effect of air-splint application on soleus muscle motoneuron reflex excitability in nondisabled subjects and subjects with cerebrovascular accidents

We investigated the effect of air-splint pressure on soleus muscle motoneuron reflex excitability in 18 nondisabled subjects with no history of neurological disease and 8 subjects with cerebrovascular accidents (CVAs). Motoneuron reflex excitability was assessed by measuring the percentage of amplitude (peak-to-peak measurement) change in the Hoffman reflex (H-reflex). Pressure was applied for 5 minutes, after which the air-splint was deflated. Ten H-reflexes were recorded and averaged for each subject before pressure application to obtain a baseline value. H-reflexes were also recorded at set intervals during and after pressure application. Two-way analyses of variance for repeated measures were used to compare each group's pressure and postpressure measurements with the baseline value. Significant F tests were followed by post hoc t tests. Analyses of variance were used to compare the nondisabled subjects' H-reflex recordings with those obtained for the subjects with CVAs. The nondisabled subjects demonstrated reductions of 55% at 1 minute, 52% at 3 minutes, and 40% at the fifth minute of pressure application. The postpressure measurements showed increases in the reflex amplitude at 1 and 3 minutes postpressure; however, by the fifth minute, the amplitude was not different from the baseline value. The subjects with CVAs demonstrated reductions of 41% at 1 minute, 48% at 3 minutes, and 52% at 5 minutes of pressure application. None of the postpressure measurements, however, were statistically different from the baseline value. A statistically significant difference was demonstrated between the nondisabled subjects and the subjects with CVAs at the first minute of pressure release.(ABSTRACT TRUNCATED AT 250 WORDS)

Motoneuron excitability modulation after desensitization of the skin by iontophoresis of lidocaine hydrochloride

Soleus motoneuron excitability was monitored after skin desensitization by iontophoresis of lidocaine hydrochloride in able-bodied subjects. Motoneuron excitability was measured by plotting H-reflex recovery curves before and after the application of lidocaine hydrochloride or a placebo. Significant H-reflex augmentation between 50 and 1,000 msec resulted after both iontophoretic application of the drug and the placebo (p less than .05). In addition, H-reflex initial recovery decreased by 20 to 30 msec in 75% of the subjects tested (p less than .05). H-reflex recovery curve facilitation lasted 30 minutes and returned to control values 45 minutes post-iontophoresis. H-reflex facilitation was not significantly different between the drug and the placebo treatments. It was concluded from these results that low-voltage, galvanic electric stimulation associated with iontophoresis predominantly caused the increase in motoneuron excitability, although other peripheral facilitatory factors may have been involved. Furthermore, cutaneous desensitization appeared not to have an effect on motoneuron excitability. This conclusion was based on the observation that similar H-reflex amplitude augmentation resulted after administration of a placebo as well as an active drug.