Potential Nutrition Contributions to Exercise-Associated Muscle Cramping in Four Recreational Half-Marathoners: A Case Series

Objectives: Nutrition-related practices and outcomes vary dramatically between athletes, and traditional beliefs regarding the role of electrolytes and hydration in exercise-associated muscle cramping (EAMC) may be hindering meaningful prevention strategies. The aim of this study was to characterize the role of carbohydrate (CHO), energy, and exertion level, in conjunction with electrolyte and hydration status to assess the role of these possible predictors of EAMC. Methods: A case series approach was used to capture pre-race and on-course food and beverage intake, pre and post-race body weight, relative perceived exertion (RPE), and history of EAMC for four recreational runners prior to and during a half-mar-athon race. Results: CHO intake, energy intake, and hydration status varied among the runners with one occurrence of EAMC. Reported pre-race CHO intake for all but one runner fell below 5 g/kg/day. Weight loss during the race was between 1.23-3.03%. Two of the four runners reported a prior history of EAMC, one of which experienced EAMC during the race. The two runners with a prior history of EAMC, also reported the lowest 3-day energy and CHO intakes. The one runner who encountered an EAMC did not experience the greatest net race sodium loss. However, this runner did have the greatest race weight loss, the greatest race sweat loss, the longest duration of activity, the lowest RPE, and suboptimal energy and CHO intakes. Conclusions: The observed case of EAMC does not appear to be entirely inconsistent with the traditional dehydration/ electrolyte loss theory. However, the in-depth characterization of each runner illustrates the complex interaction of potential predictors and also generates questions regarding the potential contribution of suboptimal energy and CHO intakes.


INTRODUCTION
Exercise-associated muscle cramping (EAMC), a specific classification of debilitating skeletal muscle spasms occurring during or after exercise, is common among all sports, genders, age groups, and environments [1].While the cause of EAMC remains unknown, dehydration along with electrolyte loss from sweating has historically been viewed as the primary contributing factor [2].Despite being based on anecdotal evidence or limited research, this widely accepted belief has formed the foundation for EAMC interventions.A survey of certified athletic trainers found that the vast majority (92.1 %) identi-International Journal of Strength and Conditioning.2021 fied either dehydration or electrolyte imbalance as the most common cause of EAMC [3].A brief snapshot of the historically ubiquitous nature of the dehydration/electrolyte loss theory-based interventions is provided in Table 1 [4][5][6][7][8][9][10][11].It is therefore not surprising that a recent survey of endurance athletes revealed that the majority (75%) believed sodium intake during endurance activities prevented EAMC [12].
Recent controlled research studies assessing dehydration using plasma volume, blood volume, and body weight changes of participants reporting EAMC do not reflect a strong association between dehydration or electrolyte loss and cramping [13][14][15][16].Studies evaluating the loss of electrolytes and electrolyte serum levels in participants from a variety of sports including football, marathon, and triathlon, have not made a connection between electro-lyte levels or electrolyte loss and the occurrence of EAMC [14][15][16][17].
Emerging science suggests altered neuromuscular control and the peripheral nervous system are key components in the etiology of EAMC, thereby challenging the electrolyte/dehydration theories that currently drive EAMC intervention strategies [1,[18][19].One emerging variable for EAMC is the effect fatigued muscles have on neuromuscular control at the alpha motor neurons of the cramping muscle.This fatigue response is associated with the buildup of metabolic byproducts in working muscles (increased CO2, decreased O2, and elevated H+ ions) during repetitive activity and results in the reduction of energy derived from ATPase for free energy which is used for maintenance of the sodium-potassium gradient in the cell membranes as well as down-regulated Ca2+ ATPase activity required to maintain excitation and contraction processes.This hindrance of muscle function results in membrane excitability and possible sustained tetany [20].
As evidence mounts against old theories behind EAMC there is also a need to reassess nutritionally modifiable causes; specifically (carbohydrate) CHO, because it is well-known that glycogen depletion results in muscle fatigue [20].Additionally, the importance of CHO on EAMC may be attributed to more than energy availability as research uncovers CHO metabolism as an integral component of cell signaling associated with muscle contraction [20][21].
Nutrition and hydration practices vary dramatically between individual athletes.Individual responses to athletic competition (i.e., sweat rate, sweat sodium concentration) vary dramatically as well [22][23][24].In addition, the risk of EAMC increases when a history of cramping is present [15,19].
As such, prior to assessing the role of possible predictors of EAMC, the nutrition and hydration practices, individual responses, and history of EAMC in endurance athletes must first be better characterized.
The purpose of this study is to gain an in-depth understanding of the nutrition-related practices and outcomes of half-marathon racers with a particular emphasis on possible predictors of EAMC.

METHODS
A case study approach was used to capture the nutrition-related practices and outcomes of half-marathon racers.All adult runners with a minimum age of 18 years registered to participate in a designated half-marathon scheduled to take place in the fall of 2018 in Colorado were queried for participation in this study.The half-marathon runners competed within age-group categories.Prize money was not awarded.The race was not a qualifying event nor a USA Track & Field (USATF) sanctioned event.Elevation at the race location was 1668 meters.The course was a relatively flat route with a less than 10-meter gain per kilometer and a total elevation gain of 38 meters.Start time temperature and weather conditions were: 11.1°C, 70% humidity, 5.6°C dew point, sunny, with no cloud cover.
This study was approved by the Institutional Review Boards at the university where the study was housed and conformed to the ethical principles set forth in the Declaration of Helsinki.Runners who volunteered to participate provided written informed consent.Six runners initially enrolled in the study; however, only four provided all the necessary information.Of these four, two were male and two were female.The running experience and age of these participants was varied.Additional participant characteristics are listed in Table 2.
A pre-race questionnaire was used to gather participant information and demographics including age, race/ethnicity, history of cramping, location of cramping, personal record for distance, estimated completion time, and altitude of residence prior to the race.The pre-race questionnaire was provided to the participants electronically after registration through email and was completed 7-14 days prior to race day.
All participants self-reported dietary intake using the MyFitnessPal™ application.Intake of food, beverages, and supplements was collected for three consecutive days leading up to the race, as well as prior to the race on the day of the race.Instructions on how to maintain the food log were provided through email.Video chat and email support were available by researcher on an as needed basis.The application provided reports detailing the total daily energy, fat, protein, carbohydrate, and sodium intake based on each participant's reported intake.A questionnaire administered by researchers immediately after the race was used to document relative perceived exertion (RPE), fluid and nutrition intake during the race, the occurrence of EAMC during the race, and the location of cramp if EAMC occurred.Reported fluid intake was adjusted by subtracting 20% of the volume for spill and fill at aid stations.
A Nokia Body+ Scale (Withings Nokia Health, Cambridge, MA, USA) was used to obtain pre and postrace body weights.Body weights were obtained with runners in race clothing with shoes removed.BMI's were calculated using self-reported heights and pre-race measured weights in the standard mathematical formula: weight (kg) / [height (m)] 2 [25].
Race weight loss for each participant was determined by subtracting their post-race weight from their pre-race weight.Race sweat was calculated by summing race weight loss and estimated fluid intake during the race.The density of fluid intake was assumed to be 1.0 g/ml [27].Sweat was also as- signed a density of 1.0 g/ml [28].
Total body sodium was approximated using 1030 mg//kg sodium for males and 990 mg/kg sodium for females [29].Sweat sodium loss was calculated by multiplying race sweat volume by the mean value for whole body sweat sodium concentrations for athletes as reported by Barenes et al [24].As such, 37.0 mmol/L was used as the value for whole body sweat sodium concentrations.Net race sodium loss was determined by subtracting sodium intake during the race from sweat sodium loss.

Runner 1
Runner 1 was a 31-year old male having four or more years of running experience with a history of completing at least one half or one full marathon prior to participating in the study race.BMI was 25.9 kg/m 2 .Elevation at his recorded residence was 1897 meters.His half marathon personal best time was 1':47", and he had no history of EAMC within the 12 months preceding the study.
For the three days prior to the race, mean energy and sodium intakes were 18213 kj (4353 kcal) and 3589 mg, respectively.CHO intake averaged 9.1 g/ kg /day (63.1%, of total energy), protein intake averaged 2.0 g/kg/day (14.1% of total energy), while fat intake averaged 1.5 g/kg/ day (22.8% of total energy).In addition, Runner 1 consumed a breakfast meal prior to race.Runner 2 was a 25-year-old female with two to three years of running experience and a history of completing at least one half or full marathon prior to participating in the study race.BMI was 22.4 kg/m 2 .Elevation at her recorded residence was 1609 meters.Her half marathon personal best time was 2':30".She had a history of EAMC within the 12 months preceding the study.Location of EAMC was reported as "abdominal".
For the three days prior to the race, mean energy and sodium intakes were 5050 kj (1207 kcal) and 2676 mg, respectively.CHO intake averaged 2.1 g/ kg /day (43.3%, of total energy), protein intake averaged 1.1 g/kg/day (22.2% of total energy), while fat intake averaged 0.7 g/kg/ day (33.2% of total energy).On the day of the race, 0 kj (0 kcal) were consumed prior to the race.
Runner 2 completed the race 6% slower than the average participant at the half marathon with a 2'31":00 finish time.Her average pace per kilometer was 7":09.At roughly 1 minute slower than her person-

Runner 3
Runner 3 was a 26-year-old male with two to three years of running experience and a history of completing at least one half or full marathon prior to participating in the study race.BMI was 24.7 kg/m 2 .Elevation at his recorded residence was 2184 meters.His half marathon personal best time was 2':07".He had no reported history of EAMC within the 12 months preceding the study.For the three days prior to the race, mean energy and sodium intakes were 10631.5 kj (2541 kcal) and 3636 mg, respectively.CHO intake averaged 3.7 g/kg /day (48.2% of total energy), protein intake averaged 1.5 g/kg/day (20.2% of total energy), while fat intake averaged 1.1 g/kg/ day (31.6% of total energy).On the day of the race, pre-race energy intake was 0 kj (0 kcal).Runner 3 had a finish time of 2':06":44 with an average pace per kilometer of 5":38.Total race time for Runner 3 was 10% faster than the mean race time and 16 seconds under his reported personal best time.EAMC was not experienced during the race with a RPE of 7 on a scale from 1-10.Runner 3 did not consume any solid or semi-solid products during the race.Estimated fluid intake during the race included 1500 ml water and 237 ml of hydration formula which provided 99.84 kcals as CHO in the form of glucose, fructose and dextrose as well as 474 mg of sodium, 55 mg of calcium, 49 mg of both potassium and magnesium.

Runner 4
Runner 4 was a 49-year-old female with less than one year of running experience and no history of completing a half or full marathon event distance prior to participating in the study race.Elevation at her recorded residence was 1777 meters.BMI was 21.7 kg/m 2 .Runner 4 reported a history of EAMC within the 12 months preceding study.The location of EAMC was described as "calf".
For the three days prior to the race, mean energy and sodium intakes were 6962 kj (1664 kcal) and 2819 mg, respectively.CHO intake averaged 2.6 g/ kg /day (39.3%, of total energy), protein intake averaged 1.2 g/kg/day (19% of total energy), while fat intake averaged 1.3 g/kg/ day (42% of total energy).Total energy intake reported before the race was 1431 kj (342 kcal) consisting of 37.4% CHO, 47.4% fat, 15.2% protein.
Runner 4 had a finish time of 2':39":17 with an average pace per kilometer of 7":33.Total race time for Runner 4 was 10% slower than the mean race time.EAMC was experienced during the race with a RPE of 4-6 on a scale from 1-10.Runner 4 did not consume any solid or semi-solid products during the race.Estimated fluid intake during the race included 828 ml water, 118 ml of cola, and 355 ml of hydration formula.Together the cola and hydration formula provided 820 kj (196 kcal) as CHO in the form of glucose, fructose and dextrose as well as 726 mg of sodium, 83 mg of calcium, and 149 mg of both potassium and magnesium.

Summary
Two of the four runners reported a prior history of EAMC while one reported a race occurrence of EAMC.All four runners lost weight during the race.Race weight loss ranged from 0.95-1.91kg or 1.23-3.03% of pre-race body weight.Estimated net race sodium losses varied between 0.71% and 3.36% of total body sodium.A summary of the exploratory EAMC predictors for all subjects is provided in Table 3.

DISCUSSION
Each runner in this study had different approaches to nutrition and hydration before and during the race.This highlights variability in nutrition practices among athletes and the need to understand their nutritional habits when reviewing EAMC occurrence.Many athletes, especially female athletes, do not meet nutritional guidelines for optimal performance [30].This study founds similar results.Three subjects reflected suboptimal to poor energy intake ranging from 43-91% of estimated needs.Fat and protein were less variable between participants and fell within or just outside of recommended intakes.CHO intake for all but one participant fell below the 5-8 g/kg recommendation associated with endurance sports lasting less than three hours per day during race season [26].
Race weight loss ranged from 1.23-3.03%with two runners not meeting the goal of limiting weight loss to less than 2% of total body weight [31].Race sweat ranged from 1778-3211 ml while the sweat sodium loss ranged from 1513-2733 mg.Overall, these observations reinforced the need for individual assessment and replacement strategies.
Two of the four runners reported a previous history of EAMC.While the two runners with a prior history of EAMC experienced the greatest net race sodium losses per kg of body weight, they also had the lowest 3-day CHO intakes, the lowest 3-day energy intakes, and had the longest durations of activity.These observations lead one to ask whether there may be an association between EAMC and factors other than hydration status and sodium loss.
While Schwellnus et al. [15] and Hoffman et al. [32] have reported a non-significant association between sex and the occurrence of EAMC, it should be noted that in the present study both runners with a ous history of EAMC were female.This observation raises the question of the possibility of menstrual cycle effecting EAMC, and given the lack of research on this topic, future studies should take this variable under consideration.In addition, the only runner to experience EAMC during the race was the oldest subject in the study.While EAMC occurrence did not differ significantly with age in an earlier study of Triathletes [15], it was found to occur at a higher rate among senior versus junior competition level rugby players.Although the authors noted differences between the senior and junior competition levels (e.g., duration of matches played, length of season), the mean age of the rugby players in the junior competition group was six years younger than that of those in the senior competition group [19].Lastly, the one runner who encountered an EAMC during the race reported a prior history of EAMC but did not experience the largest net race sodium loss.She did report suboptimal energy and CHO intakes, she had the greatest race weight loss, the greatest race sweat, the longest duration of activity, and the lowest RPE.While these observations do not appear to be entirely inconsistent with the traditional belief that dehydration and/or electrolyte loss are the main contributors to EAMC, they also generate questions regarding the potential contribution suboptimal energy and CHO intakes.The observation that the one runner who experienced EAMC also had the least running experience and the longest completion time is consistent with Schwellnus' notes of muscle fatigue being associated with an athlete experiencing levels of intensity or volume beyond the current level of fitness [15].
The observations related to activity duration and suboptimal nutrient intakes combined with emerging studies indicating possible muscle fatigue with peripheral nervous system interactions in EAMC provide reason to assess nutritional factors alongside non-nutritional factors as part of a multifactorial process in the EAMC. Figure 1 depicts this possible process.As Shirreffs and Maughan [33] point out in their recent review, the most viable hypotheses suggest EAMC originate in part as an imbalance of water and salt, an abnormal motor discharge, or both.Given the design, it is beyond the scope of this case series study to prove or disprove the validity of any proposed predictor of EAMC.The unpredictable nature and complexity of EAMC, makes laboratory studies challenging [33].As such, this case study series balances the aggregate data of all recent and relevant research on EAMC within the context of real-world outcomes and their impact on decision-making in practice.
As Langford and Bird [34] acknowledge, athletic case-studies are sometimes undervalued when appraised from a scientific viewpoint.Yet, the case study approach is an ideal means for bridging the gap between research and practice.Evidence based practice involves the integration of research, clinical expertise, and client needs [35].For the strength and conditioning practitioner, case studies can augment experience and provide insight into client perceptions and needs.Case studies can help reconcile the inconsistencies discovered between what is observed in practice and what one might expect to find based solely on research.In all, published case studies can serve as a means to enrich overall professional competence.
For the researcher, case studies and other qualitative methods can provide insight into the needs of practitioners and generate important real-world questions.While not appropriate for hypothesis testing, case studies provide insight and give a voice to complex issues.In this study, we used an in-depth approach to examine factors relevant to research on EAMC.Combined with the suggested challenges to the historic theory of EAMC, the observations of this study reinforce the need for additional research in the area of EAMC.
Limitations of this study included the inability to obtain nude post-race weights to control for soaked clothing resulting in weight loss calculations with an error factor of up to 10%.The inability to control aid station fluid intake for participants prevents accuracy in electrolyte and body weight loss data.Self-reported dietary intake and height reduce the precision of calculations.Lastly, volume and intensity of training was not documented.This would have provided insight into whether energy intakes for the participants were adequate, as well as providing a means of comparison for RPE on race day.
While the observations of this study are not entirely inconsistent with the dehydration/electrolyte loss theory, the in-depth characterization of each runner illustrates the complex interaction of potential predictors and also generates questions regarding the possible contribution of suboptimal energy and CHO intakes.For the practitioner, these observations reaffirm the need to understand the full clinical picture when reviewing EAMC occurrence.For the researcher, several possible avenues for future research present themselves.Such future research undertakings include assessing the occurrence of EAMC and the presence of chronic suboptimal nutrition, quantifying muscle glycogen within cramping muscles, and determining where nutritional and physiological predictors converge and how their confluence exerts pressure on the peripheral nervsystem leading to muscle fatigue and ultimately EAMC.

Figure 1 .
Figure 1.Hypothesized interactions of exercise-associated muscle cramping

Table 1 .
Dehydration/Electrolyte Loss Theory-Based Interventions "add extra electrolytes (GatorLytes) to their Gatorade and have them drink 20 oz (591 ml) of salted Gatorade before games and practices; and drink Gatorade during the game, at the half, and after the competition."Workout Tips for Exercise in the Heat [11] 3/15/2005 University of Colorado Sports Medicine 1/4 -1/2 tsp (1.2 -2.5 ml) table salt per liter of fluid International Journal of Strength and Conditioning.2021 Hanson, J., & Dole, A.

International Journal of Strength and Conditioning. 2021 Potential nutrition contributions to exercise-associated muscle cramping in four recreational half-marathoners: A case series.
Total race time for Runner 1 was 29% faster than the mean race time of 2':21":36 and 6 minutes faster than his half marathon personal best.EAMC was not experienced during the race with a reported RPE of 8 on a scale from 1-10.Runner 1 did not consume any solid or semi-solid products during the race.Estimated fluid intake during the race included 355 ml of water and 473 ml of hydration formula provided 835.5 kj (199.7 kcals) as CHO in the form of glucose, fructose and dextrose as well as 948 mg of sodium, 111 mg calcium, and 97 mg of both potassium and magnesium.
Total energy intake for breakfast was 4803 kj comprised of 49.4% CHO, 35.3% fat, and 15.3% protein.Dietary sodium at this meal was 832 mg.Runner 1 had a finish time of 1':39":54 with an average pace per kilometer of 4':44.

Table 2 .
Summary of participant characteristics

Table 3 .
Summary of incidence of exercise-associated muscle cramping and possible predictors