by Joseph Giandonato, MBA, MS, CSCS Faculty Member World Instructor Training Schools
Fitness professionals are faced with a multitude of dilemmas in their practice. Prominently among them lies the controversial issue of prescribing both aerobic endurance training and resistance training simultaneously, which is known as concurrent training. Concurrent training has its roots in ancient Egypt, which boasted the world’s wealthiest kingdom, buttressed by a robust military force that had prevailed over Hittite and Sea People contingents and ousted Hyskos invaders, sustaining a reign lasting over two thousand years. According to scrawlings on papyrus scrolls, Egyptian soldiers performed a variety of bodyweight exercises and running in preparation for battle, helping them surmount their opposition. On the other side of the Mediterranean, Olympic athletes in ancient Greece engaged in concurrent training, often swimming or running to improve endurance and lifting weights and performing resisted running and running in sand to improve strength. Exercises performed by ancient societies serve as the foundation for programming to this day and while an exploration of the literature demonstrates a synergism between resistance training and aerobic endurance training, the greatest challenge is striking a fine balance conducive to elicit desired adaptations, which specifically encompass improved physical preparedness and athletic performance.
Aerobic Endurance Training
In isolation, regular participation in aerobic endurance training strengthens the myocardium, resulting in increased cardiac output, which in conjunction with improved maximal oxygen consumption (VO₂max), boosts the supply of oxygenated blood to working musculature. Notable adaptations such as decreased heart rates and blood pressure, increased lactate threshold and clearance rates, improved glucose tolerance, insulin sensitivity, free fatty acid mobilization and oxidation, culminating in reduced body fat. Reduced body fat is paramount in lowering cholesterol and optimizing metabolic functioning (Dolezal & Potteiger, 1998).
Resistance training, commonly referred to as strength training, entails intermittent exercise of short durations at higher intensities interspersed with varying rest periods during a predetermined period of time (i.e., workout, training session, et cetera). In the past half century, the popularity of strength training has mushroomed as evidenced by a proliferation of health clubs throughout the industrialized world and publications showcasing its health and performance evoking capabilities in a spectrum of populations. It has become common knowledge that people of all ages, activity levels, and athletic backgrounds and goals can derive benefits from incorporating strength training within an exercise program. Regular participation in resistance training confers improvements in muscular strength, local muscular endurance, hypertrophy (Evans, 2019), strengthening of tendinous and ligamentous structures (Brumitt & Cuddeford, 2015), improved bone mineral density (Holubiac, Leuciuc, Crăciun, & Dobrescu, 2022) and coordinative abilities (Carroll, Barry, Riek, & Carson, 2001). Similar to aerobic endurance training, strength training has been shown to improve cholesterol (Mann, Beedie, & Jimenez, 2014), glucose tolerance (Craig, Everhart, & Brown, 1989), insulin sensitivity (Ishii, Yamakita, Sato, Tanaka, & Fujii, 1998), and reduce resting blood pressure (Cornelissen, Fagard, Coeckelberghs, & Vanhess, 2011).
Review of the Literature
An early investigation by Hickson (1980) garnered concerns about the compatibility of resistance training and aerobic endurance training. Concurrent training which consisted of 30 minutes of strength training five days per week and 40 minutes of endurance training performed six days per week over a period of 10 weeks was found to diminish strength development in comparison to those engaging only in strength training. However, these concerns were rebuked by later studies and a series of recent meta-analyses demonstrating that concurrent training does not compromise muscle hypertrophy and strength (Schumann, 2022) as long believed, and the resulting interference effect is largely dependent upon loading parameters, such as frequency, intensity, time, and type (Wilson, 2012). Lower aerobic endurance training volume, such as distances of 3km or less or at 18 minutes in duration was found not to inhibit strength endurance performance in comparison to greater volume entailing distances of 5 to 7km or at 30 to 42 minutes in duration (Panissa, 2014). Weekly aerobic endurance training volume was strongly correlated with decrements in strength performance (Sousa, 2020). The type of aerobic endurance training activity was also shown to be a determinant in eliciting an interference effect. Cycling was shown to inhibit strength endurance performance more than running (Panissa, 2014).
Concurrent training can be beneficial in increasing total daily caloric expenditure (Poehlman, 2002), which will hasten their resting metabolic rate, and in turn, assist with weight control (Pollock, 2000). Improvements in hemodynamic response, arterial stiffness, muscular strength (Cortez-Cooper, 2005), and submaximal exercise capacity (Beckers, 2008) have been shown among concurrent training samples. Additionally, concurrent training has also been proven effective in cardiovascular disease management (Meka, Katragradda, Cherian, & Arora, 2008) and has been shown to restore impaired aerobic endurance and strength in heart transplant patients (Chtara, 2005). Jointly incorporating aerobic endurance and strength training protocols is also postulated to be effective in improving upper and lower body strength, aerobic endurance, and balance in the elderly (Toraman, Erman, & Agyar, 2004). Further, a recent randomized controlled trial revealed that the concurrent training group significantly reduced peripheral and central diastolic blood pressure and experienced greater increases in cardiorespiratory fitness, upper and lower body strength, and lean body mass in comparison to aerobic endurance and resistance trained groups over an 8-week period (Schroeder, Franke, Sharp, & Lee, 2019). More specific to performance, concomitant modalities of aerobic endurance and resistance training have been shown to produce greater improvements in endurance performance and aerobic capacity (Chtara, 2005; Rønnestad & Mujika, 2014).
Lower volume, high-intensity strength training has been shown to evoke greater improvements in both aerobic endurance and strength performance than moderate-intensity training (Rønnestad & Mujika, 2014). Among endurance athletes, concurrent training entailing heavy or explosive strength training has been shown to improve running, cycling, and swimming economy (Rønnestad & Mujika, 2014; Giandonato, 2011).
Fitness professionals should be cognizant of the varying physiological and biomechanical demands of their clients, especially those who are engaged in competitive pursuits. For example, a distance running client who competes in local 5k races and half marathons and clients who avid lifters likely possess disparate fitness qualities, biomotor skills, and metabolic profiles. These differences are likely to be more pronounced at higher levels of competition. While both clients can and should be encouraged to engage in concurrent training, preventing undesirable adaptations, specifically reduced muscular power and strength, can be attenuated by accounting for the quaternary of loading parameters: frequency, intensity, time, and type, colloquially known as the “FITT principle”. For distance runners, lower volume, high-intensity resistance training is optimal, whereas those desiring increases in strength should have their participation in aerobic endurance training capped at no more than 18 minutes per session based on aforementioned literature. Though maximal durations of aerobic endurance training sessions may depend on the individual athlete’s training history, cardiovascular health, cardiorespiratory fitness, and performance vectors specific to their event or sport.
Additionally, if sessions are to be performed subsequently on the same day, priority should be given to which fitness qualities and biomotor skills may be insufficient or needing improvement. Further, it should be considered that performing aerobic endurance training will deplete muscle glycogen stores needed to facilitate repetitive high-intensity outputs. This is critical especially if the athlete needs to learn, practice, and ingrain technique on given movements or drills, as fatigue can impede motor learning. Ideally, same day aerobic endurance and resistance training sessions should be interpolated by a 4-to-8-hour recovery interval to reduce the interference effect and strength endurance performance. A review by Eddens, van Someren, and Howaston (2018), reported that resistance training followed by aerobic endurance training is conducive to improving lower-body dynamic strength, which is a worthy finding for clients who participate in endurance- or strength-oriented sports.
Preferably, aerobic endurance and resistance training should be performed on different days. However, if that is not possible, frequency, intensity, and volume of both aerobic endurance and strength training should be undulated throughout the year, especially during a time when the client may be competing in races or events. Additionally, fluctuations in loading parameters should account for a client’s nutritional and hormonal status, sleep quality, available time, training and chronological age, and health and injury status.
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