Sports & Exercise Research Volume 25 Number 3
Author：Andrew Nicholls; Chia-Hua Kuo
Period/Date/Page：Vol. 25 No. 3 (2023 / 09 / 30) ， Pi - vi
DOI：10.5297/ser.202309_25(3).0000
Zone 2 Training: What You Need to Know
Abstract：What Is Zone 2 Training? Zone 2 training has become a hot topic in the world of fitness and running for both seasoned athletes and newcomers. But what exactly is Zone 2 training? In simple terms, it's a form of exercise that involves working out at a relatively low intensity for an extended period, often described as a "comfortable challenge." Imagine jogging at a pace where you can hold a conversation without gasping for breath-that's the essence of Zone 2. The concept of Zone 2 training is originated in the realm of endurance sports such as cycling, triathlons, and marathons (Esteve-Lanao et al., 2017). Athletes have delved into the idea of "training intensity distribution (TID)" to optimize their athletic performance. This involves strategically incorporating different exercise intensities into their training routines. To make it more accessible, sports scientists have divided exercise intensity into distinct zones, often using heart rate as a gauge since most individuals don't have access to advanced assessments like blood lactate and oxygen consumption. Zone 1 intensity is considered dynamic recovery below the lactate threshold (50%-80% of maximum heart rate). Zone 2 intensity falls between the lactate threshold and the anaerobic threshold (80%-90% of maximum heart rate), while Zone 3 intensity is above the anaerobic threshold (above 90% of maximum heart rate; Seiler & Kjerland, 2006; Sylta et al., 2014). These zones help athletes and coaches track their training intensity and make necessary adjustments for better performance. With the advent of wearable devices like sports watches, athletes can easily monitor the time they spend in each of these training zones, making it a valuable tool in improving their training. In most fitness media and applications [APPs] like Strava, Oura ring and Whoop band, these three zones are further split into Zone 1 and Zone 2 (pre-first ventilatory threshold [Vt1] "active recovery" and "endurance"), Zone 3 and Zone 4 (Vt1-second ventilatory threshold [Vt2]-lactate threshold training, also called "tempo" and "threshold"), Zone 5 ("maximal oxygen uptake [VO_(2max)]") and some use Zone 6 and Zone 7 (maximal anaerobic). This may be confusing when reading the literature, as the common use of Zone 2 training (endurance conditioning) is actually Zone 1 in the academic literatures. The remainder of this article will refer to the common use of Zone 2 as endurance training up to a level of the Vt1. Key Questions Surrounding Zone 2 Training. 1. Is Zone 2 the Most Effective Intensity for Fat Loss and Muscle Gain? The short answer is "No." Many people confuse fat burning (fatty acid oxidation) with fat loss (Harris & Kuo, 2021). Exercise increases plasma fatty acid levels from hydrolyzing triglyceride (lipolysis) in an intensity-dependent manner-that is, the higher the intensity, the more fatty acids are released into circulation. However, the 24-hr fat burning rate (fatty acid oxidation) remains unchanged during and after exercise regardless of the intensity. You may wonder why there is a need for extra fatty acids entering circulation after high intensity exercise when it is not being oxidized to carbon dioxide? Recent studies have found that fatty acids released from fat cells are used for tissue damage repair and building new cells. Rebuilding cell membranes demands fatty acid. Blocking this process decreases wound healing (Merrick & Seale, 2020). Therefore, the higher levels of fatty acids released during high intensity exercise are more likely preserved for tissue repair and not for energy production. Based on studies employing reliable fat assessment instruments (Vissers et al., 2013), training at Zone 2 intensity is not very helpful for fat loss, despite fatty acid oxidation being greater than Zone 3 intensity. Additionally, Zone 2 training alone is not beneficial for muscle mass gain. Only high intensity workouts possess significant tissue-damage effects to elicit muscle mass gain. 2. Can Zone 2 Exercise Contribute to Anti-Aging Benefits? Again, the answer is "Not the best." If you compare cycling exercise at the intensity of Zone 2 and Zone 3, only the latter produces a senolytic effect (clearance of old or weak cells; Jean et al., 2023), which has the best potential anti-aging benefits. Additionally, studies have shown that increasing exercise intensity to a vigorous level can lower mortality rates for individuals (aged > 50 years; Byberg et al., 2009). This reminds us-we also need high intensity zone training as part of our health regimen. In conclusion, Zone 2 exercise should be viewed as a complementary component of an intensive training regimen, most suited for endurance athletes. While it has its merits for fitness, it may not be the most effective approach for fat loss or anti-aging benefits. Athletes and fitness enthusiasts should consider incorporating a variety of training intensities to achieve their specific goals and optimize their performance. (Full text)
