A total of 6548 cyclists reported a lifetime hEAMC, indicating a lifetime prevalence of 30.5 % (95 % CI: 29.8, 31.3). Of these, 3997 cyclists reported hEAMC in the past 12 months, indicating a retrospective annual incidence of 18.6 % (95 % CI: 18.1, 19.2).

The most commonly reported muscle groups affected by EAMC in cyclists with a lifetime hEAMC were the quadriceps muscles (n = 3122, 47.7 %), followed by the calf (n = 1819, 27.8 %), hamstring muscles (n = 1337, 20.4 %), and feet (n = 155, 2.4 %). For 143 (2.2 %) cyclists, the muscle groups affected by EAMC were unspecified.

The most common time period for the onset of hEAMC was during the fourth quarter of a race (n = 4152, 63.4 %), followed by after the race (n = 824, 12.6 %), third quarter (n = 819, 12.5 %), second quarter (n = 101, 1.5 %) and first quarter (n = 47, 0.7 %). Among 509 (7.8 %) cyclists, no specific timing of onset was report and 131 (2.0 %) race entrants did not specify the timing of onset related to their cramping.

The number (n), frequency ( %; 95 % CI) and prevalence ratio (PR; 95 % CI) of cyclists with hEAMC by sex and age group is shown in Table 2.

There was a significantly higher prevalence of male (34.4 %) versus female (15.8 %) cyclists with a hEAMC (PR=2.2, p < 0.0001). There was a significant difference in the prevalence of hEAMC among cyclists in the different age categories, being highest for the oldest age group (37.5 %).

The frequency ( %; 95 % CI) and prevalence ratio (PR) of cyclists with hEAMC by training/racing variables is shown in Table 3.

A number of training/racing variables were associated with an increased PR of hEAMC in cyclists. An increased number of years participating in distance cycling events of >2 h (PR=1.13 times increased risk for every 5-year increase in cycling, p < 0.0001), an increased number of years as a recreational cyclist (PR=1.08 times increased risk for every 5-year increase, p < 0.0001), faster average training speed (PR=1.02 times increased risk for every 2-km/hr increase, p = 0.0001), and increased average cycling distance in the last 12 months (PR=1.02 times increased risk for every 40-km/week increase, p = 0.0028) were associated with an increased risk of hEAMC.

The number (n), frequency ( %; 95 % CI) and PR with 95 % CI of cyclists with hEAMC by history of chronic disease, allergies, injury, and medication use is shown in Table 4.

A higher chronic disease composite score was associated with a significantly higher prevalence of hEAMC in cyclists in a “dose-dependent” fashion, meaning the higher number of chronic diseases present, the higher the risk for hEAMC (PR=1.5 times increased risk for every two additional chronic diseases present; p < 0.0001). A history of any allergies was also associated with a significantly higher prevalence of hEAMC in cyclists (PR=1.3; p < 0.0001). Cyclists with a history of a gradual onset injury had a significantly higher prevalence of hEAMC than those without a gradual onset injury (PR=1.6; p < 0.0001), as did those with a history of an acute injury compared to those without (PR=1.5; p < 0.0001). Chronic medication use (PR=1.3; p < 0.0001) and the use of medication before or during an event (PR=1.6; p < 0.0001) were both associated with a significantly higher risk for hEAMC among cyclists.

Our study is part of only two studies available that reported on the prevalence of hEAMC in cyclists.3 We report a 30.5 % lifetime prevalence of hEAMC in cyclists, which is lower compared to the 60 % reported in one study published over three decades ago.3 The lack of demographical details, training characteristics, and medical history reported in the available literature3 results in challenges when comparing the discrepancies between our findings and the available literature. However, considering the data were collected almost two decades apart, the discrepancy could be attributed to several factors including advancement in training regimes, improved nutritional strategies and potentially better cycling equipment. Studies that focussed on other endurance sports, reported higher EAMC lifetime prevalences with 67 % lifetime in triathletes3 and lower with 14.4 % in ultra marathon running20 and 8.8 % in half marathon running.21 The higher prevalence in our study could be explained by the majority of cyclists being older than 50 years, having chronic diseases and making use of chronic medications, compared to the younger populations in the running studies.20,21 However, it is difficult to make direct comparisons from these studies to the cyclists in our study due to the different nature and physiological demands of these sports. To our knowledge, this is the first study to report on the annual incidence of EAMC in cyclists (18.6 %).

The quadriceps muscle group was the most commonly affected by EAMC (47.7 %), followed by the calf muscles (27.8 %) and the hamstring muscles (20.4 %). These results are similar to those in studies investigating EAMC in distance runners,7,10 and triathletes.7 In the majority of cases, EAMC is confined to muscle groups that are actively used during an athletic event.3 Results from our study correspond with these reports, as the knee extensor group (quadriceps muscle group) is the prime mover used to generate force to the crank in the downstroke phase of cycling,22 and is therefore pivotal to cycling. In addition, EAMC usually occurs in multi-joint muscle groups that span across two joints, and contract in a shortened position, such as the gastrocnemius and quadriceps muscles.2,23 We can theorize that muscle activity in different muscle groups is different when comparing cycling to running and triathlon, which could possibly explain the differences between the distribution of EAMC in commonly affected muscles in different sports.

The majority of cyclists experienced EAMC during the final quarter of the race (63.4 %). This finding correlates with studies, which suggested that the development of EAMC is more common in the end stages of a race in marathon runners,6,23 ultra-distance runners,7 and triathletes.7 Exercising for a longer duration results in muscle overload and fatigue, which in turn can lead to the development of EAMC due to a disturbance in neuromuscular control at the level of the spinal cord.24 Our findings are in accordance with the hypothesis that muscle fatigue can lead to EAMC.

We report a significantly higher prevalence of hEAMC in male cyclists (34.4 %) compared to female cyclists (15.8 %) (PR=2.2). This finding correlates with previous studies in male vs. female distance runners.11,25 Females may be less fatigable than males when exercising at similar relative exercise intensities.26 Although speculative, this resistance to fatigue could be attributed to females having a greater proportion of type I muscle fibres that relates to better mitochondrial respiratory capacity and fatigue resistance.9,11 Therefore, evidence of muscle fatigue, resulting in altered neuromuscular control as a causative mechanism in the development of EAMC,24,27 could be a plausible explanation for this finding.

The prevalence of hEAMC was also highest in the oldest age group (PR=1.8). A previous study has shown a significantly higher hEAMC in runners in older age categories compared with runners in the younger (≤30 years) category,11 and that age is a significant indirect predictor of EAMC in distance runners.25 However, in other studies, older age has not been shown to be a risk factor associated with EAMC in runners7 or in endurance athletes with a hEAMC.12,14 The evidence regarding age remains inconclusive, and further research, especially in cyclists is needed.

A novel finding of our study, is that a higher chronic disease composite score was an independent risk factor associated with a hEAMC. For every two additional chronic diseases present, the prevalence of EAMC increased by 36 % in a “dose-dependent” manner. Our findings correlate with results from a previous study that reported an association between a history of EAMC and chronic diseases in some organ systems (cardiovascular, respiratory, GIT, nervous system or psychiatric, haematological or immune and renal) and cancer in distance runners.11 Skeletal muscle cramping is known to be associated with numerous chronic diseases,14,28,29 and associated with chronic disease in a number of organ systems. It is also an unwanted side-effect of certain medications used in the treatment of chronic diseases.11,30 Our univariate analysis’ findings supports this notion, showing a significant increased risk for hEAMC with a history of chronic medication use. However only medication use before or during and event were retained in the multivariate analysis. Muscle cramping can therefore occur due to underlying diseases or as a result of the medication used to treat these conditions.28 The potential mechanism/s to explain this relationship in recreational cyclists requires further study. In future, the chronic disease composite score could be clinically applied to identify cyclists at higher risk for injury during pre-race medical screening. This could aid in EAMC prevention through appropriate medical care, training adjustments and health education.

A second novel finding of our study was that a history of any allergies was a risk factor associated with hEAMC. This finding was similar to a previous study where it was reported that allergies were an independent risk factor associated with EAMC in distance runners.11 It has been reported that a history of allergies is common in endurance athletes.18,31 Our study shows this association (not a cause-effect) between hEAMC and allergies, and the potential mechanism is unknown. It could be postulated that both the allergy itself and the medication used to treat allergies may be underlying reason for EAMC. This is further supported by the results of our univariate analysis showing that chronic medication use, and medication use before an event were significantly associated with an increase in risk for hEAMC. Anti-histamines are commonly used to treat allergies, but have side-effects such as fatigue and drowsiness.32 We can theorize that if this type of medication is used during training and racing, medication induced fatigue could result in the development of EAMC due to a disturbance in neuromuscular control at the level of the spinal cord. This is speculative but may be a potential reason for the association between allergies and EAMC. Future research should explore the relationship between allergies, the medication used to treat allergies, and EAMC in cyclists.

Our third novel finding was that a history of cycling injury, gradual and acute onset, was an independent risk factor associated with a hEAMC. Cyclists with a history of gradual onset injury had a significantly higher prevalence of hEAMC (PR=1.4), as did cyclists with a history of an acute injury (PR=1.34). These findings correlate with studies which have reported that a history of a running injury (past or current running injury) is associated with a history of EAMC in runners and Ironman triathletes respectively.11,12 A history of a running injury is further a significant predictor for EAMC in distance runners.25 In addition, it has been reported that a history of pre-race muscle damage is associated with EAMC in ultra-marathon runners.7 It has been speculated that soft tissue injury could trigger an increase in reflex alpha motor activity,12 or that previously injured areas may be vulnerable to the development of premature fatigue due to weakness of the localized muscles,33 both of which are associated with the development of EAMC.11 However, there are no previous studies investigating the association between previous injury and EAMC in cyclists to directly compare our results to.

An increased number of years participating as a recreational cyclist was an independent risk factor associated with an increased risk of hEAMC. A higher risk for EAMC was also noted among road runners with greater number of years of running.6 However, the more experience an athlete is, the older they usually are. Therefore, our finding could be influenced by the fact that older cyclists that likely have chronic diseases and using medication before or during a race, which was also a significant risk factor. Aligned with the neuromuscular control theory, higher training intensities among athletes could lead to increased neuromuscular fatigue and potential muscle cramping.6,33,34