Paratriathlon is an endurance sport for people with a physical impairment that made its Paralympic debut in 2016 and is increasingly featured in newspaper articles (1). The athletes compete in various sports classes covering the ambulant/standing, visually impaired, and wheelchair (PTWC) categories (2). Within the PTWC, there are two sports classes for most (PTWC1) and least (PTWC2) impaired wheelchair users. During the competition, the PTWC1 starts with a time advantage before PTWC2 athletes (3). Although the ambulant/standing and visually impaired categories appear to be rather similar to conventional triathlon, the locomotion in PTWC is substantially different. Since these athletes purely rely on their upper extremities, handcycling and wheelchair racing are used as equivalent to leg cycling and running, respectively.

Previous case studies already reported training characteristics in para-swimming (4), handcycling (5, 6), wheelchair racing (7), and long-distance amputee paratriathlon (8). Training characteristics and performance development of a paratriathlon long-distance world champion (with unilateral below-the-knee amputation) were described over a period of 19 months (8). Mean training volumes were found to be lower when compared with non-disabled Olympic-distance triathletes and attained values of 8 ± 3, 6 ± 4, and 2 ± 1 h/w in swimming, cycling, and running, respectively (8). However, training practices may have changed from 2011/2012 (when the data of this case study were recorded) to the present and do not necessarily apply to triathletes with spinal cord injury (SCI).

Traumatic SCIs are defined as damage to the spinal cord due to a mechanical trauma “that temporarily or permanently causes changes in its function” (9). Depending on the level and (in)completeness of the lesion, afferent and efferent neurons as well as autonomic function are affected to a certain extent. Although paraplegia indicates that two limbs are affected (predominantly damage to thoracic, lumbar, and sacral regions), tetraplegia refers to impairment in all four limbs. The incidence of traumatic SCI was found to differ among age groups (10) and regions and is ~1 case per 100,000 individuals in Germany (11). The major causes of traumatic SCIs are accidents in motor vehicles (11). As a treatment of traumatic SCIs, surgical decompression in an early state and neuroprotective and/or regenerative strategies in the follow-up may help to reduce symptoms and side effects (12). Besides, habitual exercise was highlighted as “an effective countermeasure for addressing physical deconditioning after SCI” (13). However, since wheelchair athletes purely rely on their upper extremities, a high prevalence of upper extremity injuries was highlighted (14).

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm that accounts for approximately 15% of newly diagnosed cases of leukemia in adults (15). The incidence of CML is stated to be 1–2 cases per 100,000 adults with a mortality of 1–2% (15). The genetic origin of CML is assumed to be a fusion oncogene (BCR-ABL1) on the so-called “Philadelphia chromosome” (22q11.2) (15). The first-line treatment of CML in the chronic phase is different types of tyrosine kinase inhibitors (TKIs) that lead to a normal life expectancy for most patients (16). It was recently shown that the majority of patients with CML receiving TKI therapy experience severe fatigue that causes an increased need for sleep, a reduction of physical activity, and consequently an impaired quality of life (17). However, alternative treatments to TKIs indicated promising results in terms of molecular response and side effects (18). Besides a stable deep molecular response, CML therapy aims for treatment-free remission (16). While moderate exercise was found to be a promising tool in the treatment of acute myeloid leukemia (19), findings regarding the interaction of CML and exercise are still lacking.

This case report addresses several research gaps. First, longitudinal studies on the training and development of Paralympic athletes are generally sparse—especially over several years. Second, evidence on how paratriathletes prepare for the Paralympic Games is lacking. Third, the PTWC category demonstrates the highest difference from conventional triathlon when compared with other categories and as such requires the implementation of modified tools in exercise testing and training. Finally, to the best of our knowledge, there is no study that analyzed the acute reaction to and side effects of CML and its treatment on performance, training, and wellbeing in a highly trained athlete.

In November 2014, a 30-year-old male wheelchair athlete (ID: BL) with SCI classified as ASIA C (20) contacted our university and asked for support regarding his athletic orientation toward paratriathlon (Figure 1). BL had participated in professional wheelchair basketball for a decade and had already finished several triathlons including national championships. He wanted to have guidance in sport-specific training and testing to achieve his ultimate goal: participating in the Paralympic Games in either Rio de Janeiro (2016) or Tokyo (2020). The athlete gave written informed consent to take part in this study. Standardized guidelines for reporting were used (refer to Supplementary Material 1).

From 1990 to 2003, BL participated in motocross races. In March 2003, at the age of 18 years, he was involved in a quad bike accident that caused lumbar spine compression (ICD10-S32.01), kidney contusion (ICD10-S37.01), and incomplete paraplegia (ICD10-S34.71) with neurogenic bladder dysfunction (ICD10-N31.1) that required the permanent use of a wheelchair (ICD10-Z99.3). Immediate surgery stabilized the spine by internal fixation of the thoracolumbar junction. BL received physiotherapy, ergotherapy, and medical care during acute rehabilitation up to June 2004. He started wheelchair basketball soon after rehabilitation and played for several teams at the national level. Regular medical check-ups remained unsuspicious. In August 2013, he participated in his first sprint-distance paratriathlon.

Due to the unique demands (focus on an upper extremity) of PTWC, we modified laboratory and field tests that are commonly performed by non-disabled athletes to assess BL's physical abilities in swimming, handcycling, and wheelchair racing. Depending on his performance in paratriathlon events (discipline-specific ranking and split times) and the outcomes of the exercise tests, the training prescription focused on disciplines and/or physiological parameters that seemed to provide particular performance gains. As such, handcycling was identified as the discipline with the highest potential for improvement. Moreover, the applied training concept was oriented toward similar case studies and the international literature that highlighted the value of high training volumes performed at low intensity (5, 6, 8, 21). In our study, low intensity is oriented toward maximal fat oxidation rate (Fat_max) (22). Training camps of a 2-weeks duration were performed 2–3 times a year during the preparation period (typically between October and March). Procedures to systematically quantify his training in every discipline were applied (23).

This case report represents one of the most extensive descriptions of complex exercise testing and long-term training monitoring in Paralympic sports. We demonstrated that the physical abilities of a paratriathlete in the wheelchair category improved with increasing TL and reductions in office work duration. Training intensity distribution (TID) showed a pyramidal periodization and shift toward low-intensity training. However POBLA increased and V˙Lamax decreased over the years, V°O_2peak indicated an annual pattern and attained the highest values following the preparation period. With CML diagnosis and its treatment, TL (especially with respect to high intensities) and physical abilities substantially decreased. This hindered the athlete from competing in international events and ultimately from qualifying for the Paralympic Games in Tokyo.

A similar description was recently provided for a female paraswimmer during a Paralympic cycle (4). Although annual training hours and their development over the years were similar to this case study, the TID of the paraswimmer demonstrated an even higher percentage of low-intensity training. This is influenced by the fact that the authors used a session goal approach to determine TID, whereas a time-in-zone approach was used in this case study (49). When compared with previous studies in handcycling (5, 6), the performance gains were lower, and TID was less polarized in this study. However, these authors used time in power zones rather than heart rate zones to calculate TID, which was shown to differ between methods (50)—especially during high-intensity sessions (51). Future studies need to examine these differences in handcycling.

Training load was quantified by means of separate internal measures (TLI and TRIMP) in order to ensure comparability and standardization between paratriathlon disciplines. The high correlation between these parameters indicates an overall agreement between objective and subjective measures of TL. However, we noticed that the discrepancy between subjective and objective TL (Supplementary Material 3) coincided with acute fatigue (“heavy arms”), especially when subjective TL was substantially higher when compared with measures of objective TL. Thus, considering both types of loads and their discrepancy could be helpful for carefully monitoring daily TL and preventing acute fatigue and non-functional overreaching, especially during training camps. Despite the assumptions of previous research (52), recent findings indicate that ratios between subjective and objective measures (sRPE:TRIMP) do not provide additional information to monitor fatigue in cyclists (53). Furthermore, it was shown that TLI is not associated with alterations in physical capacity, whereas the time attained in heart rate zone 2 of 3 significantly correlated with improvements in V́O_2peak during the preparation for the HandbikeBattle (54). This is in line with the initially high V°O_2peak values (relative to his development) of BL (when a lot of zone 2 training was performed) and the fact that V°O_2peak only slightly increased with high-volume low-intensity training (2018–2019).

A similar TID as in this case study was reported for a male long-distance paratriathlete with below-the-knee-amputation (8). The increase in low-intensity percentages over time might be due to the mere increase in training volume and/or the fact that the BL became increasingly patient about performing his training sessions in the prescribed training zones. However, this might also indicate that the training prescription of BL is overly focused on high-volume rather than high-intensity training. In fact, we tried to apply high-intensity training in a block periodization, which has been shown to be an adequate training strategy to improve V°O_2max (55). However, the athlete did not tolerate more than three high-intensity interval sessions in a week due to acute fatigue. This might be due to the fact that wheelchair triathletes purely rely on their upper extremities during training and activities of daily living. Therefore, the overall higher load applied on the upper extremities increases the risk for acute fatigue, which is less severe in conventional triathletes. We experienced that the duration at a high intensity (heart rate zones 4 and 5) was higher and more easily triggered by performing wheelchair racing rather than handcycling. However, this discipline comes along with a substantially higher shoulder load (56). Due to the BL's medical complaints, the fluctuations of TL between training blocks were higher compared with previous studies (4, 6, 8), which affected training consistency, which is observed in “full-time, year-round athletes” (57).

In our case study, reducing employment increased the athlete's amount of available time and energy which allowed for more (intense) training. This increase in training duration is accompanied by an enhanced training adaptation as documented by the exercise tests. This increase in training and recovery duration is facilitated by corresponding sponsorship that was not constantly available for this athlete. Therefore, at first, training camps were tightly scheduled due to restricted training time. Although previous studies reported an average training volume during training camps of 137 ± 33% of preceding (regular) TL in the absence of acute fatigue or excessive stress (58), BL experienced a considerably higher load during the initial training camps (>200%) when he frequently reached his physical limits. From 2018 onward, we provided a less extensive and more flexible schedule in the following camps, performed daily (objective and subjective) monitoring, and implemented more (relaxing) rest days that substantially improved the feasibility, recovery, and mood. In future projects, the latter might be complemented by the Profile of Mood States Questionnaire that was successfully applied to wheelchair marathoners (7) and elite paratriathletes (58). To prevent acute fatigue and improve training quality during training camps, suitable strategies of micro-periodization were established. For example, combining high-intensity wheelchair racing in the morning followed by low-intensity handcycling was appropriate to properly exercise and recover on intensified days. Rest days consisted of an easy swim session and moderate strength training.

The characteristic pattern of VO_2peak development within each season (with the highest values observed after the preparation period) is similar to those reported in a world-class middle-distance runner (59). We assumed that the observed pattern shows a typical build-up, followed by a plateau and subsequent decline in performance during detraining. However, the athlete's paratriathlon performance in the competition was less affected over the respective years in terms of overall and split times. Jones demonstrated that world-class endurance performance can improve over several years despite a decrease/stagnation of V°O_2max as long as submaximal parameters improve (60, 61). In our case, improvements in maximal fat oxidation and/or movement economy might be the reason for the less severe decline in sport-specific performance. Especially during long rides, an improved “durability” in terms of an improved tolerance and less severe increase in heart rate during prolonged exercise were observed over the years which might be due to the high volumes of low-intensity training (62).

According to previous simulation approaches of glycolysis and oxidative phosphorylation, V˙Lamax and V°O_2max interact to determine lactate threshold (32). In simple terms, it is assumed that net lactate production results from the difference between the rate of lactate formation (as a percentage usage of V˙Lamax) and the rate of lactate removal (which is assumed to be proportional to oxygen uptake). As such, maximal lactate steady state demonstrates the highest equilibrium of lactate formation and removal (net lactate production = 0) (63). This relationship is indicated by following the development of P_OBLA in Figure 2A. If we assume that P_OBLA is improved by an increase in V°O_2peak and/or decrease in V˙Lamax (and vice versa), we can qualitatively estimate the alterations in P_OBLA. For example, P_OBLA decreased from 135 to 129 W despite a constant VO_2peak (probably) due to a huge increase in V˙Lamax immediately after a training camp. This is in line with a previous study highlighting that V˙Lamax significantly decreased after only 2 weeks of sprint interval training in trained cyclists (64). However, research on V˙Lamax adaptations is generally sparse. The reduced V˙Lamax values in our study are in accordance with previous research in ultra-endurance cycling, demonstrating a decrease in V˙Lamax during a prolonged period of high-volume low-intensity training (65). Since V˙Lamax was found to be increased by various forms of resistance exercise (66), an intensified fine-tuning of strength and sport-specific training contents was applied. Our preliminary findings demonstrated that V˙Lamax is affected by exercise modality, highest in swimming and lowest in wheelchair racing, which might be due to the usage of muscle mass. Although the reliability of V˙Lamax has been sufficiently assessed in handcycling (26, 27), future studies need to examine V˙Lamax in swimming and wheelchair racing.

There are several limitations of this case report that need to be mentioned. Given the high number of contextual variables (e.g., medical, logistical, nutritional, and social), training was frequently adapted to the acute circumstances, which makes it challenging to highlight causations. In PTWC triathlon, the need for various materials (handcycling and racing wheelchair), dependence on barrier-free facilities, and the pure focus on upper extremity locomotion demonstrate substantial constraints that the athletes have to overcome in order to be competitive. Especially as far as side effects of CML and its treatment are concerned, it is likely that experienced fatigue and reduced physical activity interact to ultimately decrease performance (17). Furthermore, TID is purely based on heart rate zones and as such hardly comparable with studies using session goals or time in power zone approaches.

In conclusion, this case report illustrates the training monitoring and performance development of a triathlete with SCI and CML during a Paralympic cycle. We demonstrated the need for careful training prescription in PTWC triathletes to improve performance in the absence of acute fatigue, overuse injuries, and non-functional overreaching. We encouraged athletes and coaches to refrain from overly extensive and/or intense training schedules and recommend the application of objective and subjective monitoring tools. This is stressed by the high demands on the upper extremities in wheelchair triathletes, who require special support, sponsors, and training prescriptions.

“In my opinion, having a great team of coaches and supporters was essential for gaining the last boost during the highs and lows of this journey. The same applies to those who gave medical assistance, which was highly important—especially in my case. Health complaints (e.g., bladder infections) kept me from performing in training and competitions, which was also mentally challenging. Accepting CML diagnosis and its consequences for fulfilling my goal took some time, even though my SCI-background helped to cope. I would like to share my experiences with sports and diseases to inspire others in the future.”

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.

Ethical review and approval was not required for the study on human participants in accordance with the local legislation and institutional requirements. The patients/participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

OJQ planned the triathlon-specific training, participated in training camps, collected and analyzed the data, and drafted the manuscript. BL volunteered in this study, performed the training and exercise tests, and provided insights into his perspective. FL and PB were handlers at competitions and participated in training camps. FL provided logistical planning. PB planned and coached strength and conditioning contents and advised BL on aspects of nutrition and supplements. TF provided medical check-ups and supervised medical aspects of the project. All authors reviewed, edited, and approved the manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.