Effects of Hydration Changes on Neuromuscular Function of Athletes With Low Water Intake
Trial Snapshot
- Phase
- Not Applicable
- Status
- Recruiting
- Enrollment
- 50
- Locations
- 1
- Primary Endpoint
- Maximum voluntary isometric contraction - Knee extension
Study Overview
Brief Summary
Greater muscular strength and power are relevant qualities for athletic success and decreased injury rate. It is known that dehydration impairs muscular strength and power, although the explanation for this association is not entirely clear. Besides morphological factors, strength production also depends on neural factors which in turn can be affected by dehydration. Some studies tested the effects of dehydration on neuromuscular function using electromyography (EMG) analysis. However, there is no consensus among those studies.
Additionally, exercise may disturb water balance. This can further lead to dehydration if the athlete does not properly rehydrate. In this sense, the scientific evidence has identified people who are considered low drinkers that may be more susceptible to cellular shrinkage, potentially impairing health and performance. Thus, it would be expected that athletes regularly exposed to lower amounts of water intake would have beneficial effects in both performance and health if higher water ingestion was promoted, namely an improved neuromuscular function via enhanced cellular hydration. However, any potential benefit of increasing water intake on neuromuscular function is still to be determined using well-designed experimental studies and state-of-the-art methods.
Lastly, there is no consensus regarding the diagnosis of dehydration in athletes. The identification of simple indices to measure dehydration in athletes is crucial as many may be inaccurately diagnosed.
Detailed Description
Athletes are dependent on muscular strength as it is associated with a higher rate of force development and muscular power, general and specific sports skills performance, and decreased injury rates. There is scientific evidence showing that a hypohydrated state [i.e., 2 to 3% of body mass loss (BML) attributed to water loss] impairs muscular strength and power. However, how this reduction affects athletic performance remains in question.
We know that muscular strength development is derived from a combination of morphological (muscle cross-sectional area, muscle architecture, and musculotendinous stiffness) and neural factors (motor unit recruitment, synchronization, and firing frequency). Thus, neural factors may be one possible explanation for the effects of dehydration. In fact, there is biological plausibility for this relation as dehydration may affect the electrolyte's concentration (particularly potassium and sodium) within intra- and extracellular spaces, leading to an alteration of the membrane electrochemical potential.
Although some studies have tested the effects of hydration changes on neuromuscular function using electromyography (EMG) analysis, there is still no consensus among them. Some authors showed effects of dehydration on muscle endurance and EMG signal, including reduction in EMG mean power frequency (MPF) and an accelerated rate of root-mean square (RMS), possibly meaning reduced membrane excitability and an accelerated central mediated regulation of motor unit activity. While others did not find any effect of dehydration on EMG values. Thus, experimental studies using well-designed trials and state-of-the-art technology are required to better understand the effects of acute dehydration on neuromuscular function, specifically in athletes.
Maintenance of a euhydrated state is crucial for the proper physiological functioning of the body, being achieved by physiological and behavioral factors. However, exercise can disturb water balance, particularly when performed in hot environments, increasing water loss. This can further lead to dehydration if the athlete does not properly rehydrate. In this sense, the scientific evidence has identified people who are considered low drinkers (i.e., people who are exposed to a low regular water intake) and high drinkers (i.e., people who are exposed to a high regular water intake). These differences in water intake lead to different physiological responses such as serum arginine vasopressin (AVP) levels and also in mood states. Although no specific total water intake guidelines have been established for athletes, when compared to the European Food Safety Authority guidelines for water intake in healthy adults, they do not meet the guidelines, specifically when higher hydration needs are considered. As mentioned before, AVP has been used to distinguish low drinkers from high drinkers, namely elevated plasma AVP in low drinkers suggesting intracellular dehydration.
In fact, changes in total body water (TBW) and its compartments [i.e., intracellular water (ICW) and the extracellular water (ECW)] have been studied regarding their impact on sports performance. Silva and colleagues observed that judo athletes who decrease TBW, namely by decreasing ICW, were those that decreased upper-body power, regardless of changes in weight and arms' lean-soft tissue. Also, ICW was the only body water compartment whose reductions explained the higher probability of losing >2% of forearm maximal strength, independently of changes in weight and arms' lean-soft tissue. Finally, ICW was also considered the main predictor of strength and jumping height over the season in national-level athletes. Thus, ICW and cellular hydration appear to play a relevant role in athletic power and strength, although further research is needed to link these structural fluid compartments with changes in the hydration status and its connection with neuromuscular function.
Study Design
- Study Type
- Interventional
- Allocation
- Randomized
- Intervention Model
- Parallel
- Primary Purpose
- Basic Science
- Masking
- None
Masking Description
Given the nature of the study, it is not possible to blind neither participants nor research team members regarding the allocated groups.
Eligibility Criteria
- Ages
- 18 Years to 35 Years (Adult)
- Sex
- All
- Accepts Healthy Volunteers
- Yes
Inclusion Criteria
- •Highly trained athletes (i.e., participating in national and international championships and/or ≥6 h of training per week)
- •Athletes considered low drinkers (i.e., total water intake ≤ 35ml/kg/)
- •Aged between 18 and 35 years
- •Living in Lisbon and/or its surroundings
- •All women should have a (self-reported) normal menstrual cycle (i.e., cycles at median intervals of less than 35 days)
- •Completion of the sport's medical examination
Exclusion Criteria
- •Total water intake above 35ml/kg/day.
- •Clinical history compatible with exertional heat illness (i.e., heat stroke, heat exhaustion, hyperthermia, among other events that suggest poor response to thermically challenging environments)
- •Taking medication known to alter the normal fluid-electrolyte balance, plasma osmolality, urinary osmolality, or the chronotropic response to exercise (e.g., diuretics, antidiuretics, laxatives, oral contraceptives, drugs to control blood pressure (39)
- •Exhibiting self-reported metabolic disorders or malfunction of salivary glands
- •Active smoking status
- •Unwilling to abstain from alcohol during this study
- •Respiratory disorders, including asthma
- •Injuries that would limit exercise performance
- •Mechanical prostheses
- •Pregnancy /planning to get pregnant within the next 8 months
- •Having been pregnant within the past 6 months or breastfeeding
- •Failure to complete the dietary intake and physical activity recording
- •Unable to communicate with local study staff
- •Needle phobia
- •Inability to complete the study within the designated time frame because of plans to move out of the study area or occurrence of competition periods during the study timeframe
- •Inability to attend the visits/appointments and evaluation measurements
Arms & Interventions
Experimental group
Over a 4-day period, participants randomly assigned to the experimental group will be instructed to maintain normal solid food choices, but to increase water intake to achieve a total water intake of ≥45ml/kg/day. Prepared bottles of water with the required amount will be given to each participant every morning and collected empty the following day. Instructions to drink small amounts of water every hour be transmitted.
Adherence to instructions regarding water intake will be determined by the return of drinking bottles, analysis of daily food records, assessment of water flux (i.e., collecting urines after subjects being dosed with deuterium), and daily screening questions. These samples will be delivered on a subsequent morning during a daily laboratory visit to collect urine and saliva samples, as well as BI assessment. On the 4th day, participants will perform a neuromuscular function assessment.
Intervention: Increasing water intake (Other)
Control group
Participants randomly assigned to the control group will be instructed to maintain normal solid food choices and water intake based on their average intake reported on the food records. Adherence to instructions regarding water intake will be determined and assessments performed will occur as mentioned previously for the experimental group.
Outcomes
Primary Outcomes
Maximum voluntary isometric contraction - Knee extension
Time Frame: 3 weeks
For the lower body strength, participants will be assessed on a Biodex System 3 Pro isokinetic dynamometer (Biodex Medical Systems, Shirley, NY). The participants will remain seated with the belts positioned on the thorax, abdomen, thigh, and above the knee on the side that is being evaluated to limit the knee movement. Each testing session will begin with a dynamic warm-up, consisting of 5min of submaximal cycle-ergometry set at 25 W followed by a 5 min of resting before starting the testing protocol. First, a MVIC 5-s voluntary knee extension (knee at 70o for the extension). Verbal encouragement and audible feedback from the dynamometer software will be provided to each participant.
Maximum voluntary isometric contraction - Knee flexion
Time Frame: 3 weeks
After the maximum voluntary isometric contraction for knee extension, participants will be asked to perform a MVIC 5-s voluntary knee flexion (30o for the flexion). This test will be performed with 3min of pause after the MVIC of knee extension.
5 submaximal isometric repetitions of knee extension
Time Frame: 3 weeks
5 submaximal isometric repetitions will me measuredfrom MVIC of baseline and MVIC of that day: 1) 30s at 20% of MVIC; 2) 30s at 40% of MVIC; 3) 10s at 60% of MVIC; 4) 10s at 80% of MVIC; 5) 10s at 100% of MVIC. Between repetitions a pause of 1 min will be performed between repetitions while a pause of 3 min will be performed between sets.
EMG signals - Root mean square
Time Frame: 3 weeks
During the legs' strength assessment, EMG signals will be recorded (EMG Delsys Trigno Avanti, Delsys Incorporated, USA) from the vastus lateralis (VL), rectus femoris (RF), vastus medialis (VM), and biceps femoris (BF) muscles in accordance with the guidelines of the Surface EMG for the Non-invasive Assessment of Muscles (SENIAM). The electrodes will be placed before the 5 min of resting after the dynamic warm-up. EMG signals from each muscle will be pre-amplified (gain 1000), band-pass filtered (20-450 Hz), and A/D converted at 1kHz (MP100, BIOPAC Systems Inc., Goleta, CA). AcqKnowledge 4.3.1 software will be used for data collection and processing (BIOPAC Systems Inc., Goleta, CA).
EMG signals - Mean power frequency
Time Frame: 3 weeks
During the legs' strength assessment, EMG signals will be recorded (EMG Delsys Trigno Avanti, Delsys Incorporated, USA) from the vastus lateralis (VL), rectus femoris (RF), vastus medialis (VM), and biceps femoris (BF) muscles in accordance with the guidelines of the Surface EMG for the Non-invasive Assessment of Muscles (SENIAM). The electrodes will be placed before the 5 min of resting after the dynamic warm-up. EMG signals from each muscle will be pre-amplified (gain 1000), band-pass filtered (20-450 Hz), and A/D converted at 1kHz (MP100, BIOPAC Systems Inc., Goleta, CA). AcqKnowledge 4.3.1 software will be used for data collection and processing (BIOPAC Systems Inc., Goleta, CA).
Rate of torque development (RTD) for knee extension and flexion
Time Frame: 3 weeks
In both MVIC for knee extension and flexion, the participants will be instructed to avoid any countermovement prior to test and will be asked to exert their maximum force as fast and hard as possible, to obtain both maximal torque and rate of torque development (RTD). Verbal encouragement and audible feedback from the dynamometer software will be provided to each participant.
Fatigue task
Time Frame: 3 weeks
Last, and after a pause of 5 min, participants will perform an isometric contraction at 40% of MVIC (measured on the day) until to exhaustion. Exhaustion will be considered if a decrease of more than 10% of MVIC for more than 10s is observed.
Handgrip strength
Time Frame: 3 weeks
The handgrip strength test measures maximum voluntary isometric contraction (MVIC) of the hand and forearm muscles. Handgrip will be performed using a portable hand dynamometer (TSD121C; Biopac Systems, Goleta, CA, USA). Participants will be assessed on both hands alternately, in a standing position. Prior to the test, the grip dynamometer will be adjusted to the size of the hand of each subject. Handgrip strength assessment will be conducted with the subject standing up with the arms in a neutral position (halfway between supine and pronation position). Each participant will be assessed on both hands alternately until reaching 3 attempts for each hand. In each attempt, the subject will exert the maximal grip strength on the handgrip dynamometer with the assessed hand for 5s. After each attempt, there will be a resting period of 60s that will be used both for recovery and for changing the handgrip dynamometer to the opposite hand.
Secondary Outcomes
- Food records(3 weeks)
- Cardiorespiratory Fitness Test(3 weeks)
- Plasma osmolality(3 weeks)
- Urine osmolality(3 weeks)
- Thirst and mouth dryness(3 weeks)
- Serum arginine vasopressin(3 weeks)
- Extracellular water(3 weeks)
- Intracellular water(3 weeks)
- Saliva osmolality(3 weeks)
- Serum sodium concentration(3 weeks)
- Total body water(3 weeks)
- Phase angle(3 weeks)
- Impedance(3 weeks)
- Resistance(3 weeks)
- Reactance(3 weeks)
- Classic Bioimpedance Vector Analysis (BIVA)(3 weeks)
- Fat mass(3 weeks)
- Body volume(3 weeks)
- Bone mineral content(3 weeks)
- Fat free mass(3 weeks)
- Profile state of mood(3 weeks)