Concurrent Training in Field Based Sports

It is well understood that a prerequisite for field sport-based athletes to build elite performance, must develop and be able to sustain high levels of both maximal strength and aerobic capacity to succeed and achieve high levels of performance. However, concurrent development of strength and endurance within a typical training programme often presents a big physiological challenge. The "interference effect” refers to the decrease of strength and hypertrophy adaptations when endurance training is performed alongside resistance training (Hickson, 1980). The subsequent research surrounding the interference effect has often complicated the original proposition of what the interference effect means, yielding a nuanced body of evidence with significant implications for practitioners who work with field sport-based athletes. This review analyses two central themes: (1) the mechanistic basis of the interference effect and (2) practical programming strategies to mitigate this effect. 

Mechanistic Basis of Interference Effect

Historical Context and Early Evidence

The initial studies in this area conducted by Hickson (1980) demonstrates that two athletes who combined strength and endurance training simultaneously, experienced significant lower strength gain compared to athletes who undertook a training programme that focused on strength training alone, despite those who combined the two had the same volume of strength training. This idea prompted subsequent research to this effect. Early theories often explained this effect due to overtraining and the accumulation of fatigue, and the idea that the concurrent training method exceeded the athlete’s recovery capacity (Leveritt et al., 1999). However, this explanation has often been criticised for providing insufficient evidence as research has matured, and molecular biology has since provided more concise mechanistic accounts for this issue. 

The AMPK, mTORC1 Conflict

The most substantial and compelling explanation for the interference effect has been the conflict of AMP-activated protein kinase (AMPK) and m-TORC1 signalling pathways. Endurance training and activities activates AMPK, a energy sensor that promotes the catabolic process, and critically it is has been cited in research to suppress the activation of m-TORC1, which is the principle anabolic signalling pathway stimulated by resistance training, which stimulates muscle protein synthesis and hypertrophy (Coffey and Hawley, 2007). The conflict between these two molecular compounds has been the most prevalent argument and explanation for why training strength and endurance simultaneously might blunt the adaptations that field-based athletes are trying to achieve, regardless of their nutritional intake and recovery habits. 

The understanding of this phenomenon was extended by demonstrating that the interference effect is modality-dependent (Fyfe, Bishop and Stepto, 2014). This research demonstrated that running-based endurance training in particular had a more profound and noticeable interference on lower body strength in comparison to other activities such as cycling, likely due to the greater eccentric stress which is inherently associated with running, causing greater residual muscle damage that impairs the subsequent training quality for resistance based training. For rugby and football contexts this is particularly pertinent, where running based conditioning is often the most common modality of conditioning. The practical implications is that the modality of endurance training chosen is a variable and culpable of moderating interference which has often been neglected within field sport-based practice. 

Fibre Type and Volume Considerations

A meta-analysis conducted by Wilson et al. (2012) provided an important quantitative perspective of this effect, providing evidence that concurrent training significantly reduced hypertrophy and strength adaptations relative to strength training alone, with the effect size being most pronounced for explosive and power-related outcomes. This research highlighted that fast twitch (Type II) muscle fibres were disproportionately affected, highlighting a direct relevance to field sports, where high velocity force production underpins some key areas of performance (sprinting, jumping and contact performance). The interference to these areas, power quality specifically, highlights the importance of athlete profiling. For rugby forwards for example, whose potential demands emphasise maximal force production, the interference with this specific adaptation they are trying to chase may be more consequential in comparison to a winger whose aerobic base requirements are comparatively higher. 

Programming Strategies to Mitigate Interference

Exercise Order and Session Sequencing

One of the most controllable variables to mitigate interference is the ordering of concurrent training stimuli within a particular session. According to Chtara et al. (2008) the effect of exercise sequencing and order in athletes who were recreationally trained found that strength performed before endurance produced significantly higher improvements in running economy and maximal aerobic power, compared with the reverse order. In addition to this finding, when strength development was the primary adaptation, as typically sought out for during pre-season phases, resistance training performed first is widely recommended to mitigate the interference on mTORC1 signalling prior to AMPK activation (Coffey and Hawley, 2007), therefore for practitioners, they should try and align session order with the adaptation they are primarily trying to achieve first during a phase of concurrent training. 

The concept of training separation, whether this is dividing strength and endurance stimuli across any specific day or training week, has also seen empirical evidence. Separating strength and endurance sessions for a minimum of six hours has been shown to substantially reduce interference for both strength and endurance training in rugby union players, preserving strength and power adaptations across an eight- week preseason block (Robineau et al., 2016). The ecological validity of this study gives a sport specific example of how the interference effect can be mitigated by periodising training more effectively. For practitioners this recommendation clearly outlines that the spacing between sessions can be influential in mitigating the interference effect on concurrent training, and risk reduction strategies for field sport environments. 

Modalities of Endurance Training and HIIT

Common modalities to improve aerobic capacity within an athlete represents a programming consideration which is often underappreciated. High-intensity interval training (HIIT) has been popularised as an efficient strategy for developing an athlete’s aerobic capacity whilst reducing interference with strength training compared to traditional modules of high-volume continuous training (Laursen and Jenkins, 2012). Very low volume HIIT protocols have been shown to improve aerobic capacity significantly with substantially lower overall training volumes (Metcalfe et al., 2011) which reduces the total AMPK activation burden that is posed onto the athlete. This could mean for field sport athletes who accumulate considerable running loads, whether that is through technical or tactical sessions, this modality of training of training has implications for managing concurrent training stress without sacrificing aerobic development. 

In addition to HIIT training being used to combat modalities of training: Rowing, Cycling, Ski-erg, Assault Bikes, have been used to reduce high impact running loads for athletes. Research suggests that this may attenuate interference in the lower body musculature during concurrent training blocks (Fyfe, Bishop and Stepto, 2014). Whilst field-based sports inherently demand run specific fitness, the general preparation for strength-based phases of their training may benefit from non-specific aerobic modalities that preserve the mechanical integrity of the lower limb’s mechanics for resistance training. This approach highlights that training stimulus may not need to always mirror the competitive demands, more specifically when the goal is to train physical qualities simultaneously. 

Periodisation and Phase Potentiation

Another approach to manage the interference effect in field sports is the application of block periodisation, which aims to emphasise one physical quality over another across different distinct training phases. The theoretical foundation of block periodisation argues that concurrent training stimuli achieves superior adaptive outcomes rather than disturbing them (Issurin, 2010), through allowing complete expression of each quality's adaptive potential. Practically this might involve an accumulation block of periodised aerobic base development, followed by a transitional phase which emphasises maximal strength, leading to a block focused on expressing speed and power. This model is increasingly being adopted within rugby programmes typically. 

Structured periodisation is a common operation within elite rugby contexts, where the model has demonstrated improvements in maximal strength and players aerobic capacity across a full season (Smart, Hopkins and Gill, 2013). This approach showed evidence of reduced interference-related actuations compared to non-periodised concurrent programmes. The key takeaway from this is that the interference is not eliminated, rather it is managed temporarily. Qualities can still be developed in parallel to one another. However, during bouts of intensive development, phases should be strategically offset to reduce molecular conflict during any given phase. 

Applied Recommendations for Best Practice

The research provides extensive evidence that converges on several recommendations that practitioners can take on board when working within field-based sport environments. Strength and endurance sessions, where feasible, should be separated by a six-hour window to allow AMPK activity to stabilise before resistance-based training is undertaken (Robineau et al., 2016). Secondly, for endurance-based training, during a phase that prioritises strength development a non-running or low impact aerobic work approach might be more suitable to reduce any mechanical interference, especially in the lower limbs. Lastly, HIIT should replace traditional volume based continuous training where the aerobic adaptations are a key area of development alongside maximal strength training, with the capacity to stimulate aerobic adaptations during periods of lower overall volumes of training loads. 

Long-term athletic development frameworks could incorporate block periodisation models that pose great emphasis of strength and development across an annual plan, to reduce the chronic concurrent exposure during intensive development windows (Issurin, 2010). This could also incorporate neuromuscular readiness assessments alongside subjective wellbeing measures to inform programming adjustments where schedules have constraints on session separation. 

Conclusion

The interference effect remains one of the most practically consequential phenomena in applied sports and exercise science. Early observations to molecular insights of AMPK and mTORC1, field-based sports have shifted from descriptive observations towards applying mechanically informed and context driven prescription of programmes. For the field sport practitioners, the interference effect may not be a constraint that is insurmountable, rather it is a variable that can be responded to by well-informed programming and scheduling, modality selection and the way programmes are periodised. Qualities such as explosive power are the most vulnerable to this effect making the risk ever present in sports that are heavily dominated by contact. Effective concurrent training should be a product of good programming not a side-effect.

References

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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 Medicine, 44(6), 743–762. https://doi.org/10.1007/s40279-014-0162-1

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Leveritt, M., Abernethy, P. J., Barry, B. K., & Logan, P. A. (1999). Concurrent Strength and Endurance Training. Sports Medicine, 28(6), 413–427. https://doi.org/10.2165/00007256-199928060-00004

Metcalfe, R. S., Babraj, J. A., Fawkner, S. G., & Vollaard, N. B. J. (2011). Towards the Minimal Amount of Exercise for Improving Metabolic health: Beneficial Effects of reduced-exertion high-intensity Interval Training. European Journal of Applied Physiology, 112(7), 2767–2775. https://doi.org/10.1007/s00421-011-2254-z

Robineau, J., Babault, N., Piscione, J., Lacome, M., & Bigard, A. X. (2016). Specific Training Effects of Concurrent Aerobic and Strength Exercises Depend on Recovery Duration. Journal of Strength and Conditioning Research, 30(3), 672–683. https://doi.org/10.1519/jsc.0000000000000798

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Wilson, J. M., Marin, P. J., Rhea, M. R., Wilson, S. M. C., Loenneke, J. P., & Anderson, J. C. (2012). Concurrent Training: a Meta-Analysis Examining Interference of Aerobic and Resistance Exercises. Journal of Strength and Conditioning Research, 26(8), 2293–2307. https://doi.org/10.1519/jsc.0b013e31823a3e2d