There are a lot of reasons a strength athlete may want to incorporate cardio into their resistance training program. But what does the research say about concurrent training and how it affects strength?
Concurrent training is the combination of resistance training and endurance training. The aim of this review is to provide evidence-based information that will cover concurrent training considerations, possible adaptations to HIIT, possible concerns and recommendations for strength athletes (with an emphasis on heavy resistance training combined with HIIT for strength athletes, like powerlifters).
What is HIIT?
Spoiler: Because this review will suggest HIIT as the mode of cardio, let’s define it first. High intensity interval training (HIIT) utilizes high intensity bouts of exercise (i.e. 10 seconds to 5 minutes) repeated at an intensity greater than the anaerobic threshold with brief recovery periods in between. Typically, HIIT training incorporates running or cycling based modes. The idea is to place added stress on the physiological systems that are used in endurance exercise in a repetitive fashion (more than what is actually required to complete the activity).
Benefits of HIIT
According to Buchheit and Laursen, HIIT may be “one of the most effective forms of exercise for improving physical performance in athletes” (Fleck & Kramer, 2014). In addition to improving overall cardiorespiratory health, possibly improving running economy and speed, as well as body composition changes, there are many reasons an athlete would want to incorporate endurance training. For untrained athletes, if the athlete is looking to enhance speed or anaerobic endurance, HIIT can improve endurance performance greater than continuous training alone (Laursen and Jenkins, 2002). This is related to up regulation of both oxidative and glycolytic energy systems, which means improved energy state in working muscles and greater preservation of high energy phosphates. Additionally, enhanced peak anaerobic power and output and VO2Max seem to be common responses to HIIT in untrained individuals. Another benefit of HIIT training is that an athlete can have rapid improvements despite misconception that it takes years. For example: VO2Max increased after only 10 weeks of HIIT alternating 40 min cycling intervals at VO2Max1 day and 40 min high intensity running the next. Even a single session had skeletal muscle adaptations occur (Laursen and Jenkins, 2002).
For trained athletes, benefits include overall endurance performance, improved heat tolerance, greater use of fatty acids, enhanced oxidative enzyme activity, improved skeletal muscle buffering capacity, adaptation of the CNS and endocrine systems, increases in myoglobin, capillary density (may improve lactate removal), and changes in fiber type characteristics (Laursen and Jenkins, 2002). In short, strength athletes can benefit from incorporating this type of training; however, there are considerations that should be examined first.
When prescribing HIIT, it’s important to consider the athlete’s training status, goal and overall demands of total programming. Strength and power athletes may want to limit aerobic training because concurrent use of heavy resistance and intense aerobic exercise can weaken the quality of signals needed for anabolism. Specifically, the high oxidative stress that comes with high intensity may hamper power development (Fleck & Kramer, 2014). Keep in mind that this is especially at high velocities of muscle actions and may occur after weeks of concurrent training. However, this will depend on the athlete’s training status (incompatibility is more prominent in untrained individuals), overall volume and frequency and whether or not both types are performed on the same day. Also keep in mind that there may also be an upper genetic limit, which goes without saying for any fitness parameter.
Much research has claimed that aerobic exercise hinders maximum muscle fiber growth when combined with resistance training; however, this is when concurrent aerobic exercise mode is not HIIT (Babock, 2012). Although not fully understood, it may be because the responsiveness of satellite cells. When satellite cells were assessed, their response to resistance training was reduced when it was performed after aerobic exercise. Data concluded that perhaps the environment created by aerobic exercise that was not HIIT (continuous, steady state or distance) may attenuate addition of myonuclei that is important for muscle fiber growth (Babock, 2012). Therefore, it may be reasonable for a strength athlete to limit continuous or steady state aerobic exercise to avoid said interference.
Additionally, it has been hypothesized that resistance training and endurance training may not be compatible as it blocks some processes that help increase strength. Although not proven in humans yet, the theory is that an athlete’s skeletal muscle may not be able to adapt to both types of training at the same time because many of the adaptations are different. Over time, this may lead to impairment of strength development (Leveritt, 1999).
That said, before eliminating endurance training from a strength athlete’s program completely, there are additional considerations. As previously mentioned, trained strength athletes may be less likely to have interference with simultaneous resistance training and either HIIT or continuous endurance. Evidence has shown that athletes with a history of resistance training were able to increase strength after concurrent training for a short period of time (Petre, 2018). So, if an athlete is experienced, and if they incorporate a short concurrent training block, they may be less likely to have levels of strength affected.
Also, in this study, it was mentioned that HIIT would be a more efficient intervention as it was the only instance where VO2max improved (Petre, 2018). When it comes to a duration, there is evidence that suggests HIIT that is completed after heavy resistance training may not interfere with strength when the duration of two months. In this instance, interval cycling was performed after resistance training (Tsitkanou, 2016). Although it has been concluded that high volume endurance training that is continuous and often may interfere with strength adaptations that come with stand-alone resistance training, conversely, low volume or HIIT, may have little to no affect when recommendations are followed (Methenitis, 2018). It’s important to note that this study also favored cycling as the mode of HIIT as it demonstrated the least interference with resistance training. In short, it is important to consider the status of the athlete (trained), the duration of the endurance training (short), as well as the mode of training (HIIT, cycling).
Though not the focus of this review, it may also be useful to state that strength training does not negatively affect endurance performance, including the development of peak oxygen consumption. In fact, resistance training programs may help endurance athletes by improving performance, preventing injuries and increasing lactic acid threshold (Fleck and Kraemer, 2014).
In the event that a strength athlete concurrently trains, there are ways to reduce compatibility issues. Keep in mind that many athletes do not appear to be able to adapt to both modes of training in high frequencies and intensities for a long duration of time.
- Each athlete should have regular assessments of training status to make improvements to the HIIT program.
- Sufficient recovery is necessary to be able to detect benefits from HIIT (fatigue and overtraining can play a role in decreased performance).
- Although a shorter rest period may mean less work achieved, it has also been suggested that supramaximal HIIT with short rest periods may maximally tax aerobic and anaerobic capacities.
- An active recovery may be justified to help facilitate lactate removal. Keep in mind that when you incorporate activities what produce high amounts of lactic acid (like HIIT) your body learns how to use lactic acid as a fuel source more efficiently.
- A taper is essential following a phase of increased volume and intensity. Example: reduce volume by at least 75% during a 6-day taper (there was no difference between 50-75% reduction) (Laursen and Jenkins, 2002).
- Higher and longer intensities of interval training should be periodized as they can interfere with strength, power and muscle size, especially in those untrained (Fleck & Kramer, 2014.
- It has been noted that several minutes above 90% of VO2max for an optimal stimulus.
- Reduce intensity and volume of HIIT, while considering goals of the athlete (example: if peaking for a meet, it would be reasonable to schedule HIIT training further away from this block).
- Use non-running forms of aerobic conditioning when you can (cycling is favorable).
- Perform lower body resistance training on days that lower body aerobic endurance training is not being performed / upper body resistance training on days that lower body aerobic endurance training is being performed.
- Take 1-2 days off for complete rest and recovery.
- Position each type of training on separate days, which may help avoid interference (24 hours).
- If time is a factor, and if training cannot be separated, resistance training should come before HIIT (Murlasits, 2018).
In this review, a thorough discussion of concurrent training related to strength athletes is presented. It is possible, that concurrent training can have little interference with strength if proper guidelines are followed. This will include close monitoring and assessment of the athlete’s program, addressing the athlete’s needs and status (individualized), placing an emphasis on HIIT training versus continuous endurance training as well as proper rest and recovery. Whichever method of concurrent training that is chosen, it is important that the athlete and coach understand each phase so recommendations can be followed, and positive results can be achieved.