Concurrent training in soccer: Is there interference, and how can you maximize resistance and endurance training gains?written by Nikolay Georgiev.

Nikolay Georgiev is a final-year Health and Performance Science Student at UCD. In his blog, Nick outlines his views on concurrent training using preseason in soccer as an example. 

Soccer Demands

Soccer players need a robust aerobic system and sufficient levels of strength/power. Yet, concurrently developing endurance and strength/power is often difficult, especially in preseason, when players may return deconditioned after a decreased training stimulus during the off-season. High-intensity interval training (HIIT) (Table 1) is increasingly favored for improving endurance over moderate-intensity continuous training (MICT). HIIT is a more time-efficient training method and effectively activates molecular pathways similar to MICT (MacInnis & Gibala, 2017).

Concurrent Training

Simultaneously integrating resistance and endurance exercise is termed concurrent training (CT). The interference effect first observed in the 1980s (Hickson, 1980), suggests that concurrent endurance training can reduce strength gains compared to performing RT alone. Conversely, RT may enhance endurance performance by improving neuromuscular performance and running economy (Aagaard & Andersen, 2010). Nevertheless, extensive evidence suggests that training (e.g., intensity, volume, modality, recovery time) and non-training (e.g., training status and nutrient availability) factors influence the interference effect (Fyfe et al., 2014, Seipp et al., 2023). Understanding these elements and the molecular basis of training adaptations is key to minimizing interference. 

Potential Mechanisms for The Interference Effect

Two distinct hypotheses likely explain the interference effect:

• neuromuscular theory: compromised quality of the strength session 

• The molecular theory: molecular and/or biological events that inhibit muscle protein synthesis (MPS) and/or exacerbate muscle protein breakdown (MPB).

This blog focuses on the latter. However, briefly, despite the acute effect being primarily associated with reduced strength session quality, residual RT neuromuscular fatigue may impair running economy/kinematics (Doma et al., 2017) and/or increase injury risk (Lovell et al., 2016) in subsequent endurance sessions. Therefore, coaches should prioritize key HIIT or strength sessions when necessary.

Molecular Adaptations Underpinning Strength and Endurance

Exercise adaptations arise from repeated transient increases in transcript abundance post-workout (Baar, 2014; Hawley et al, 2014). Elevated mRNA levels during recovery drive protein synthesis, resulting in structural remodeling and long-term adaptations.

Strength training can elevate IGF-1 levels, activating the PI3K-Akt pathway and stimulating mTOR. Specifically, mTORC1, described as the primary contributor to RT adaptations (i.e., muscle hypertrophy), activates S6K and 4E-BP, ultimately promoting MPS.

Endurance training skeletal muscle adaptations are associated with signaling pathways that regulate mitochondrial biogenesis (via activation of the transcriptional coactivator PGC-1α, including the AMPK, CaMK, SIRT, and p38 MAPK pathways).

Training Adaptation Specificity

The repeated activation of exercise-induced molecular signaling pathways promotes distinct structural and functional phenotypic adaptations specific to each exercise mode. Atherton et al. (2005) demonstrated this concept by reporting that exposure of rodent skeletal muscle to high-frequency stimulation (60×3 s at 100Hz) selectively activated the anabolic Akt/mTOR signaling pathway, whereas low-frequency continuous stimulation (3h at 10Hz) activated and inhibited the AMPK/PGC-1α and Akt/mTOR signaling pathways, respectively. Subsequently, the existence of an ‘AMPK–Akt master-switch mechanism was proposed to regulate muscle adaptations from strength and endurance training.

However, in humans, little evidence exists for this hypothesis. Apro et al. (2015) reported a five-fold increase in the S6K1 expression has been reported in moderately trained individuals after HIIT. Also, mechanotransduction and leucine availability can stimulate mTORC1 independently of Akt, while low muscle glycogen may activate AMPK (Fyfe et al., 2014). AMPK may decrease MPS or increase MPB by activating TSC2 and MuRF-1, MaFbx, and ULK1, respectively, all of which inhibit mTOR (Fyfe et al., 2014). Therefore, the ‘AMPK–Akt ‘master-switch’ model seems too simplistic to explain training adaptation responses, and the various training and non-training variables likely influence the interference effect.

Variables Influencing the Interference Effect

Intensity. Coffey et al. (2009) reported that performing cycling HIIT before RT attenuated anabolic signaling more so than when employing cycling MICT (Coffey et al., 2009). Conversely, Fyfe et al. (2016) demonstrated that HIIT and MICT concurrent exercise did not compromise mTORC1 signaling during early recovery compared with RE alone. 

Nutrition. The cycling sprints in Coffey’s study were performed in a fasted state which stimulates AMPK. Moderately trained individuals performing HIIT and RT in a fed state with 3h of rest similarly increased AMPK and Akt/mTOR signaling response compared to RT alone (Lee et al., 2024). 

Within Session Order. Lee’s observations were also irrespective of the within-session order. Given the difference in AMPK endurance training (<3) and mTOR resistance training (>24h) responses (Fyfe et al., 2014), performing RT after endurance exercise may allow these early recovery anabolic responses to proceed unimpeded. However, HIIT-induced neuromuscular fatigue may last for at least <6h (Buchheit & Laursen, 2013), depending on the factors modulating the residual fatigue from HIIT (Figure 1). Since an extended recovery period likely reduces HIIT residual fatigue, when RT is prioritized it should precede endurance training. 

Volume. Some observe no interference with <2 endurance sessions/week (Hakkinen et al., 2003), while others report decreased strength gains with >3 sessions/week (Hickson, 1980). Since pre-season typically emphasizes endurance volume, low-volume HIIT may help minimize interference while still enhancing aerobic capacity.

Figure 1. A conceptual framework outlining the practical factors that could impact residual fatigue after high-intensity interval training (HIIT), which may, in turn, impair subsequent strength training performance. Adapted from Laursen & Buchheit 2019, pp. 126.

HIIT and Resistance Training.

Strength/power are arguably more important qualities than hypertrophy in soccer. When concurrently using HIIT and RT, assuming sufficient rest, the interference effect can be minimized by RT with high loads (4x6 RM) (Seipp et al., 2023), and using repeated-sprint training (RST) and sprint interval training (SIT) training (Vechin et al., 2021). 

Modality. Wilson et al. (2012) suggest that running causes greater interference than cycling, yet Sabag et al. (2018) reported the opposite. Conversely, Chen et al. (2024) found that running HIIT + RT is optimal for improving strength, power, and hypertrophy. The inconsistent findings are likely due to the different methodologies. Team sports athletes could benefit more from a modality that mimics their sport. Hence, in soccer running might be preferred.

Training Age. The interference effect likely increases with training age. In untrained individuals, similar mTORC1 signaling responses are observed between resistance and endurance exercise (Camera et al., 2010), whereas in highly-trained individuals, the mTORC1 pathway is preferentially activated by only RT (Vissing et al., 2013). 

Conclusion

While concurrent training can reduce resistance training adaptations, well-designed programs, considering the discussed training and non-training variables, may minimize interference. Practical recommendations are presented in Table 3. 

• References

  Figure 1. A conceptual framework outlining the practical factors that could impact residual fatigue after high-intensity interval training (HIIT), which may, in turn, impair subsequent strength training performance. Adapted from Laursen & Buchheit 2019, pp. 126.

  HIIT and Resistance Training.

  Strength/power are arguably more important qualities than hypertrophy in soccer. When concurrently using HIIT and RT, assuming sufficient rest, the interference effect can be minimized by RT with high loads (4x6 RM) (Seipp et al., 2023), and using repeated-sprint training (RST) and sprint interval training (SIT) training (Vechin et al., 2021). 

  Modality. Wilson et al. (2012) suggest that running causes greater interference than cycling, yet Sabag et al. (2018) reported the opposite. Conversely, Chen et al. (2024) found that running HIIT + RT is optimal for improving strength, power, and hypertrophy. The inconsistent findings are likely due to the different methodologies. Team sports athletes could benefit more from a modality that mimics their sport. Hence, in soccer running might be preferred.

  Training Age. The interference effect likely increases with training age. In untrained individuals, similar mTORC1 signaling responses are observed between resistance and endurance exercise (Camera et al., 2010), whereas in highly-trained individuals, the mTORC1 pathway is preferentially activated by only RT (Vissing et al., 2013). 

  Conclusion

  While concurrent training can reduce resistance training adaptations, well-designed programs, considering the discussed training and non-training variables, may minimize interference. Practical recommendations are presented in Table 3. 

  References

  Aagaard, P., & Andersen, J. L. (2010). Effects of strength training on endurance capacity in top-level endurance athletes. Scand J Med Sci Sports, 20 Suppl 2, 39-47. https://doi.org/10.1111/j.1600-0838.2010.01197.x 

  Apró, W., Moberg, M., Hamilton, D. L., Ekblom, B., van Hall, G., Holmberg, H. C., & Blomstrand, E. (2015). Resistance exercise-induced S6K1 kinase activity is not inhibited in human skeletal muscle despite prior activation of AMPK by high-intensity interval cycling. Am J Physiol Endocrinol Metab, 308(6), E470-481. https://doi.org/10.1152/ajpendo.00486.2014 

  Atherton, P. J., Babraj, J., Smith, K., Singh, J., Rennie, M. J., & Wackerhage, H. (2005). Selective activation of AMPK-PGC-1alpha or PKB-TSC2-mTOR signaling can explain specific adaptive responses to endurance or resistance training-like electrical muscle stimulation. Faseb j, 19(7), 786-788. https://doi.org/10.1096/fj.04-2179fje 

  Baar, K. (2014). Using molecular biology to maximize concurrent training. Sports Med, 44 Suppl 2(Suppl 2), S117-125. https://doi.org/10.1007/s40279-014-0252-0 

  Buchheit, M., & Laursen, P. B. (2013). High-intensity interval training, solutions to the programming puzzle. Part II: anaerobic energy, neuromuscular load and practical applications. Sports Med, 43(10), 927-954. https://doi.org/10.1007/s40279-013-0066-5 

  Camera, D. M., Edge, J., Short, M. J., Hawley, J. A., & Coffey, V. G. (2010). Early time course of Akt phosphorylation after endurance and resistance exercise. Med Sci Sports Exerc, 42(10), 1843-1852. https://doi.org/10.1249/MSS.0b013e3181d964e4 

  Chen, Y., Feng, X., Huang, L., Wang, K., & Mi, J. (2024). Comparative efficacy of concurrent training types on lower limb strength and muscular hypertrophy: A systematic review and network meta-analysis. J Exerc Sci Fit, 22(1), 86-96. https://doi.org/10.1016/j.jesf.2023.12.005 

  Coffey, V. G., Jemiolo, B., Edge, J., Garnham, A. P., Trappe, S. W., & Hawley, J. A. (2009). Effect of consecutive repeated sprint and resistance exercise bouts on acute adaptive responses in human skeletal muscle. Am J Physiol Regul Integr Comp Physiol, 297(5), R1441-1451. https://doi.org/10.1152/ajpregu.00351.2009 

  Coffey, V. G., Pilegaard, H., Garnham, A. P., O'Brien, B. J., & Hawley, J. A. (2009). Consecutive bouts of diverse contractile activity alter acute responses in human skeletal muscle. J Appl Physiol (1985), 106(4), 1187-1197. https://doi.org/10.1152/japplphysiol.91221.2008 

  Doma, K., Deakin, G. B., & Bentley, D. J. (2017). Implications of Impaired Endurance Performance following Single Bouts of Resistance Training: An Alternate Concurrent Training Perspective. Sports Med, 47(11), 2187-2200. https://doi.org/10.1007/s40279-017-0758-3 

  Fyfe, J. J., Bishop, D. J., & Stepto, N. K. (2014). Interference between concurrent resistance and endurance exercise: molecular bases and the role of individual training variables. Sports Med, 44(6), 743-762. https://doi.org/10.1007/s40279-014-0162-1 

  Fyfe, J. J., Bishop, D. J., Zacharewicz, E., Russell, A. P., & Stepto, N. K. (2016). Concurrent exercise incorporating high-intensity interval or continuous training modulates mTORC1 signaling and microRNA expression in human skeletal muscle. Am J Physiol Regul Integr Comp Physiol, 310(11), R1297-1311. https://doi.org/10.1152/ajpregu.00479.2015 

  Häkkinen, K., Alen, M., Kraemer, W. J., Gorostiaga, E., Izquierdo, M., Rusko, H., Mikkola, J., Häkkinen, A., Valkeinen, H., Kaarakainen, E., Romu, S., Erola, V., Ahtiainen, J., & Paavolainen, L. (2003). Neuromuscular adaptations during concurrent strength and endurance training versus strength training. Eur J Appl Physiol, 89(1), 42-52. https://doi.org/10.1007/s00421-002-0751-9 

  Hawley, J. A., Hargreaves, M., Joyner, M. J., & Zierath, J. R. (2014). Integrative biology of exercise. Cell, 159(4), 738-749. https://doi.org/10.1016/j.cell.2014.10.029 

  Hickson, R. C. (1980). Interference of strength development by simultaneously training for strength and endurance. Eur J Appl Physiol Occup Physiol, 45(2-3), 255-263. https://doi.org/10.1007/bf00421333 

  Lee, M. J., Caruana, N. J., Saner, N. J., Kuang, J., Stokes, T., McLeod, J. C., Oikawa, S. Y., Bishop, D. J., Bartlett, J. D., & Phillips, S. M. (2024). Resistance-only and concurrent exercise induce similar myofibrillar protein synthesis rates and associated molecular responses in moderately active men before and after training. Faseb j, 38(1), e23392. https://doi.org/10.1096/fj.202302024R 

  Lovell, R., Siegler, J. C., Knox, M., Brennan, S., & Marshall, P. W. (2016). Acute neuromuscular and performance responses to Nordic hamstring exercises completed before or after football training. J Sports Sci, 34(24), 2286-2294. https://doi.org/10.1080/02640414.2016.1191661 

  MacInnis, M. J., & Gibala, M. J. (2017). Physiological adaptations to interval training and the role of exercise intensity. J Physiol, 595(9), 2915-2930. https://doi.org/10.1113/jp273196 

  Sabag, A., Najafi, A., Michael, S., Esgin, T., Halaki, M., & Hackett, D. (2018). The compatibility of concurrent high intensity interval training and resistance training for muscular strength and hypertrophy: a systematic review and meta-analysis. J Sports Sci, 36(21), 2472-2483. https://doi.org/10.1080/02640414.2018.1464636 

  Seipp, D., Quittmann, O. J., Fasold, F., & Klatt, S. (2023). Concurrent training in team sports: A systematic review. International Journal of Sports Science & Coaching, 18(4), 1342-1364. https://doi.org/10.1177/17479541221099846 

  Vechin, F. C., Conceição, M. S., Telles, G. D., Libardi, C. A., & Ugrinowitsch, C. (2021). Interference Phenomenon with Concurrent Strength and High-Intensity Interval Training-Based Aerobic Training: An Updated Model. Sports Med, 51(4), 599-605. https://doi.org/10.1007/s40279-020-01421-6 

  Vissing, K., McGee, S., Farup, J., Kjølhede, T., Vendelbo, M., & Jessen, N. (2013). Differentiated mTOR but not AMPK signaling after strength vs endurance exercise in training-accustomed individuals. Scand J Med Sci Sports, 23(3), 355-366. https://doi.org/10.1111/j.1600-0838.2011.01395.x 

  Wilson, J. M., Marin, P. J., Rhea, M. R., Wilson, S. M., Loenneke, J. P., & Anderson, J. C. (2012). Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. J Strength Cond Res, 26(8), 2293-2307. https://doi.org/10.1519/JSC.0b013e31823a3e2d 

Background:

I initially studied BSc Sport and Exercise Science at the University of Bath in 2017 but left after one semester to pursue a professional soccer career in Bulgaria. Achieving my childhood dream of becoming a professional goalkeeper was an incredible experience, but in May 2021, I decided to transition into strength and conditioning coaching.

Since September 2022, I have been studying BSc Health and Performance Science at UCD, gaining invaluable S&C coaching experience with the UCD Freshers’ Soccer Team and UCD Men’s Rowing Team. I also spent a year and a half as an S&C coach in the Shamrock Rovers Academy, where working with elite youth athletes in a high-performance environment allowed me to grow immensely as a practitioner.

Now in my final year, I am completing an internship with the UCD Men’s and Women’s Field Hockey Teams and recently started working as a sports scientist with the senior football team of Kilmacud Crokes.