Long-distance running performance is largely reliant on a complex interaction of physiological factors, including maximal oxygen uptake (VO₂max), lactate threshold and running economy, as well as biomechanical parameters such as stride length and frequency, ground contact time or vertical oscillation, which contribute to optimized force production and reduced energy cost, supporting a more economical and faster running (Joyner, 1991; Santos-Concejero et al., 2014).

During running, there is a substantial eccentric component (Black et al., 2022), which occurs when the force applied to the muscle exceeds the tension produced by the muscle itself, resulting in the lengthening of the musculotendinous system (Hody et al., 2019; Bontemps et al., 2020). This eccentric component has been reported to induce high mechanical strain, resulting in moderate to severe exercise-induced muscle damage (Black et al., 2022; Bontemps et al., 2020; Millet and Lepers, 2004), that triggers acute biomechanical changes such as an increased stride frequency and decreased stride length (Kim et al., 2018). Similarly, there is evidence that prolonged strenuous exercise induces metabolic stress (Knechtle and Nikolaidis, 2018; Sadowska-Krępa et al., 2021) and promotes the production of reactive oxygen species (ROS) in response to the systemic inflammation increment caused by muscle damage (Powers et al., 2016).

Previous research has reported increases in the concentration of creatine kinase (CK), lactate dehydrogenase (LDH), transaminases, pro-inflammatory and anti-inflammatory cytokines such as the interleukin-6 (IL-6), chemokines, and associated inflammatory mediators after strenuous endurance exercise (Sugama et al., 2012; Suzuki et al., 2003; Tominaga et al., 2021; Lecina et al., 2022). All this, ultimately, leads to substantial muscle soreness, inflammation and swelling, and the loss of muscle function, which can persist for several days (Black et al., 2022; Kyröläinen et al., 2000). Since muscle damage in runners results in greater performance impairments than other exercises with little or no impact (Black et al., 2022; Millet and Lepers, 2004), it has been suggested that it may even be the main performance constraint in ultra-endurance running events (Tiller and Millet, 2025).

In that regard, advanced footwear technology (AFT) development in the last few years has been a revolution (Rodrigo-Carranza et al., 2022a). AFT shoes are characterised by the presence of a curved carbon fiber plate aimed at optimising longitudinal bending stiffness (Rodrigo-Carranza et al., 2022b; Rodrigo-Carranza et al., 2024) embedded in lightweight, resilient midsole foams that enhance cushioning and mechanical energy return (Rodrigo-Carranza et al., 2022b; Hoogkamer et al., 2018; Winn et al., 2025). Numerous studies have reported that AFT can improve running economy and performance (Rodrigo-Carranza et al., 2022a; Rodrigo-Carranza et al., 2022b; Rodrigo-Carranza et al., 2024; Hoogkamer et al., 2018), and it may also reduce fatigue, muscle damage and soreness in recreational runners after a marathon (Kirby et al., 2019). The question arises whether AFT also provides a small biomarker response for muscle damage and metabolic and oxidative stress during long-distance running in experienced runners.

Therefore, in this study we aimed to analyse the influence of two different AFT-which differ in their mechanical properties-on biomechanical, neuromuscular, muscle damage, metabolic and oxidative stress markers in experienced runners during a strenuous long-distance running bout. We hypothesized that the difference in mechanical characteristics, such as energy return or resistance, of these shoe models would elicit differential biochemical and biomarker responses in experienced runners.

The main finding of this study was that both AFT shoes tested, the Cloudboom Strike and the Cloudboom Echo 3 models, resulted in minimum muscle damage, metabolic and oxidative stress, as the only muscle damage biomarker that increased post-exercise was the CK (Figure 2), with no changes in other muscle damage (LDH and ALT), inflammation (IL-6), metabolic (cortisol) or oxidative stress biomarkers (TAS) (Figures 2, 3). This contrasts with previous research reporting that strenuous long-distance running can lead to significant LDH (Jürgenson et al., 2021), ALT (Jastrzębski et al., 2015), IL-6 and cortisol (Vezzoli et al., 2016) and oxidative stress increases (Vezzoli et al., 2016). Therefore, according to our results, both AFT models appear to provide notable minimal biomarker response after a 60-min treadmill run with regards to reducing muscle damage, oxidative and metabolic stress, soreness, and inflammation, which may indicate an attenuated biomarker response when compared to previous studies of traditional footwear.

It is well-known that strenuous prolonged running results in moderate to dramatic increments in muscle damage biomarkers post-exercise (Brancaccio et al., 2010; Miles et al., 2008), and the activity of enzymes such as the CK, LDH or ALT is commonly used in that regard (Noakes et al., 1983; Kim et al., 2007; Kim et al., 2009). Previous research has reported changes as high as 10-fold–20-fold increases in CK activity 24-h post strenuous long-distance running (Jastrzębski et al., 2015; Kłapcińska et al., 2013), which contrasts with the relatively small <2-fold increase observed in this study (Figure 2). Similarly, the literature reports four-fold increases in ALT activity and significant LDH increases after long-distance running (Lippi et al., 2011), indicative of considerable damage to the skeletal muscles, whereas we found no differences pre- and post-exercise in ALT or LDH values when running in either of the AFT shoe conditions (Figure 2).

Strenuous exercise has also been reported to induce oxidative stress through enhanced formation of ROS (Leeuwenburgh and Heinecke, 2001). Previous studies have found increased oxidative stress in long-distance runners (Briviba et al., 2005; Liu et al., 1999; Vuorimaa et al., 1999), and ironman competitors (Reichhold et al., 2009) which contrasts with our findings, as we found no differences in TAS pre-post in either the Cloudboom Strike and the Cloudboom Echo 3 shoe models after the prolonged effort test (Figure 3). Oxidative stress is suggested to induce inflammation by activating different transcription factors, resulting in the expression of inflammatory pathway genes (Hussain et al., 2016). Therefore, the apparently attenuated post-exercise oxidative stress observed in this study may partially explain the unchanged pro-inflammatory cytokine IL-6 measurements after the prolonged effort test in the CS and CE shoe conditions (Figure 2).

In that sense, one possible explanation could be the fact that in the previous literature, the footwear models were not considered AFT as in our study, and the characteristics attributed (resilience and energy return) could impact the muscle damage biomarkers. However, in our study, a control condition (non-AFT) was not included; therefore, methodological differences between studies—such as exercise duration, blood sampling intervals, and the training status of participants—may partly account for the smaller biomarker responses observed here. Accordingly, while our findings suggest that both AFT models are associated with attenuated biomarker changes after a 60-min treadmill run, these differences might not be attributed exclusively to footwear effects but also considered within the context of protocol design and participant characteristics.

Increased delayed onset muscle soreness (DOMS), muscle damage and inflammation have been observed during intense and/or long-distance running as well (Kirby et al., 2019). All this leads to acute to chronic loss of muscle function, (Black et al., 2022; Kyröläinen et al., 2000), which is, ultimately, associated with running performance impairments (Black et al., 2022; Millet and Lepers, 2004; Tiller and Millet, 2025). The fact that both CS and CE conditions in this study resulted in relatively small muscle soreness post-exercise (mean ± SD: 2.0 ± 1.47 vs. 2.79 ± 1.34; median [IQR]: 2.0 [IQR: 0.75–3.0] vs 3.0 [IQR: 2.0–3.0] in Likert scale points) is, therefore, in agreement with evidence indicating that softer surfaces -as the ones of CS and CE due to their high cushioning-may lessen the DOMS response (Brown et al., 2017; Skinner et al., 2015). Our results are also in line with Kirby et al., (Kirby et al., 2019), who found that after a marathon, post-race indicators of muscle damage and associated inflammation were lower (LDH<15% and IL-6 <43%), in runners wearing AFT shoes (Nike Vaporfly 4%) when compared to traditional shoes (Nike Zoom Pegasus). They also reported that AFT resulted in less overall fatigue and less soreness (<22% and <46%).

Our results and the aforementioned studies clearly suggest that AFT shoes confer significant benefit effects against exercise-induced muscle damage, oxidative stress and inflammation. However, this is the first study comparing how different longitudinal bending stiffness -one of the key aspects of AFT shoes when compared to traditional ones-affects such responses. The Cloudboom Echo 3 (CE) is a stiffer (73.29 vs. 61.41 N mm^-1) and less resistant to deformation (24.15 vs. 20.22 mm) model, whereas the Cloudboom Strike (CS) stores more energy (12.23 vs. 10.03 J) and displays a higher energy return (10.46 vs. 8.27 J) (Table 1).

Interestingly, participants reported lower DOMS 24 h post-exercise with the CS shoe model when compared to CE (p = 0.016; ES = 0.71, moderate effect). However, since we found no differences either relative increments or absolute post-visit CK (333.75 ± 214.89 vs. 307.94 ± 218.33 U·L^-1), LDH (194.73 ± 23.49 vs. 192.32 ± 26.01 U·L^-1), IL-6 (2.72 ± 0.90 vs. 2.36 ± 1.04 pg mL^-1), ALT (24.90 ± 6.48 vs. 24.33 ± 6.60 U·L^-1), cortisol (17.34 ± 3.91 vs. 16.46 ± 2.87 μg·dL^-1) or TAS (1.67 ± 0.11 vs. 1.62 ± 0.12 mmol·L^-1) (Figures 4, 5), there must be another biomarker no measured in this study leading to that higher muscle soreness observed in the Cloudboom Echo 3 shoe model.

Despite the attenuated exercise-induced muscle damage responses and the lack of differences between conditions, there were significant biomechanical changes during the prolonged effort in this study. During the 60-min effort, participants tended to increase their SF (0.17%, 169.25 ± 2.15 vs. 169.54 ± 1.88 steps·min^-1) and consequently reduce their SL (0.19%, 154.00 ± 3.00 vs. 153.70 ± 2.70 cm). Due fatigue, participants also experienced a significant increase in DF (0.71%, 28.00% ± 0.60% vs. 28.20% ± 0.50%) and a decrease in FT (1.06%, 156.61 ± 5.74 vs. 154.95 ± 5.14 ms), VO (1.20%, 9.19 ± 0.36 vs. 9.08 ± 0.32 cm) and ID (3.37%, 66.22 ± 20.52 vs. 64.02 ± 20.95 ms). These types of adaptations to fatigue have been previously reported and suggest that for constant speed during a prolonged run, trained athletes prefer to increase the number of steps and reduce their length, as it requires less intensity of vertical impacts (Giandolini et al., 2016; Morin et al., 2011). Although these fatigue-induced biomechanical adaptations, no differences were detected between footwear conditions and shoe × time interaction, indicating that these temporal adaptations likely reflect generalized fatigue responses rather than effects of footwear mechanic characteristics. This absence of condition effects may be partly explained by the limited sensitivity of the selected spatiotemporal and trunk accelerometry-derived variables to capture shoe-related differences. Furthermore, the 60-min duration, while sufficient to elicit moderate fatigue, might not replicate the biomechanical alterations expected during longer running protocols, such as half-marathon or marathon distances, where cumulative effects become more evident.

In this regard, Cartón-Llorente et al. (2022) found that, when trained athletes performed a 60 min time trial on a treadmill, no biomechanical adaptations occurred during the test. The reason why may be that participants were allowed to make variations on speed during the test. In longer efforts, such as a 24 h treadmill run, previous literature shows that participants tend to evolve to a running style which characterised by a higher step frequency and less vertical oscillation (Morin et al., 2011). These mechanisms have been also reported in ultra-marathon racing conditions (Giandolini et al., 2016), and seem to be protective adaptations to reduce the intensity of vertical impacts at each step (Patoz et al., 2023) and be more efficient for running economy (Folland et al., 2017). Although in this study, our test was a significantly shorter effort than an ultramarathon or a 24 h treadmill run, we found similar adaptations: the reduction in VO, FT, DF and ID, which imply that athletes made a transition to a more protective running style requiring less intensity of vertical impacts., and seem to be protective adaptations to reduce the intensity of vertical impacts at each step (Patoz et al., 2023) and be more efficient for running economy (Folland et al., 2017).

This study faced several limitations. These include the relatively small sample (n = 12) for some of the biomarkers, such as IL-6, and the fact that this study only tested men. This makes it difficult to generalise the results obtained as AFT might potentially have greater performance effects in women (Mason et al., 2024). Also, despite participants were asked to mimic their food, hydration and sleep patterns within the tests, no monitoring of these aspects was performed, which could have influenced the obtained results. Similarly, biomechanical parameters measured in this study might vary from overground running and motorized treadmill running (Riley et al., 2008). In addition, the outcome measures related to muscle damage, metabolic and oxidative stress are relatively basic, and it may be that other biomarkers related to inflammation and soreness (C-reactive protein, aspartate aminotransferase, myoglobin, troponin.) or oxidative stress (protein carbonyl, thiobarbituric acid reactive substances, total antioxidant capacity.), not measured here, are determinants of the DOMS differences observed between condition in this study. Also, the chosen timing for blood samples and DOMS assessment may have missed transient peaks in IL-6 and cortisol for blood samples, and 24–72 h peak dynamics for subjective measures. Future studies should include immediate and 2–6 h post-exercise blood samples and more timepoints for DOMS dynamics, as well as other objective metrics such as pressure pain threshold or creatine kinase correlation.

In conclusion, according to our results, both the Cloudboom Strike and the Cloudboom Echo 3 AFT shoe models appear to provide notable benefits with regard to reducing muscle damage, oxidative and metabolic stress, soreness, and inflammation in highly trained/national level -tier 3- male runners. Despite the lack of differences between conditions in the muscle damage, oxidative and metabolic stress biomarkers measured, the Cloudboom Strike implied significantly lower DOMS 24 h post-exercise than the Cloudboom Echo 3. These differences might be attributed to a biomarker that was not measured in this protocol. In addition, and in agreement with previous research, in both conditions, during the 60-min run, participants tended to increase their SF, reduce their SL, and, due to fatigue, also experienced a significant increase in DF and a decrease in FT, VO, and ID. However, there were no biomechanical differences between conditions.