Less than recommended training of aerobic fitness and muscle strength: What to expect?

According to the recommendations by The American College of Sports Medicine (ACSM), people need to exercise in long sessions, performed at high intensity, to achieve maximum oxygen uptake (VO2max, “Fitness”)1 and muscle strength.1, 2 This implies more than the 30-minute daily activity generally recommended by health authorities. But if one wants to stay fit, how often, how long and how intense should the training be to give a satisfactory result? In a BBC program from 2012 (http://www.bbc.com/news/health-17177251),3 it was claimed that good aerobic fitness may be achieved by riding an ergometer bike at maximum intensity for 1 minute 3 times per week. To find out what is lost by working out less and gained by working out more, at least 3 doses of exercise are required. Ideally, one could wish to stratify sampled results from the world literature into homogeneous groups. Group data could then be meta-analysed, followed by regression analysis of group means. From this, one might estimate loss of training effect associated with a given reduction in, for example, training volume. However, both training variables and study protocols are numerous and disparate, and there exist no internationally agreed standards for training protocols. One can vary frequency, duration and intensity, length of study period, sex and age of study participants. Moreover, a multitude of different exercises are available, and different outcome variables are used like heart rate, time to fatigue, maximum force (1 RM), oxygen uptake, lactate threshold, etc. Consequently, no dose-response studies of training along such lines have been published, to our knowledge. We therefore elected to find studies of randomized dose-response studies with at least 3 dose levels (deposited in the Zenodo database).4 The works we found (16 studies of aerobic fitness and 27 strength studies) supported the commonly held view, namely that one is trainable even at an advanced age, and that the fitness and strength effects from exercise are relatively better when the starting point is at low level rather than a high level of performance. In general, the results were better when the aerobic fitness and strength training were performed at high intensity, and high exercise volume often increased the effect. However, there were unexpected findings, as pointed out below. We found few studies that compared the effect of varying the frequency of training days (sessions), either concerning fitness or strength training. Increasing the number of sessions did not consistently increase the training effect. Concerning duration, an average session of fitness training could give satisfactory results; 4 (near) maximal 20-seconds spurts, with 10-seconds intermissions were as good as 2 and 5 spurts.5 For strength training, some studies showed no clear relationship between number or duration of workout bouts and improvement. For example, young, well-trained men with 4 training days per week for 10 weeks and 3, 6 or 12 sets per session had a 5.7%, 5.2% and 6.7% gain in strength, respectively.6 However, most studies found that longer workouts were rewarded by increased strength. Usually, high-intensity interval training is best for training aerobic fitness. In biking, it turned out that three 3-minute interval cycles over the course of 18 minutes could provide a better aerobic fitness boost than 45 minutes of continuous cycling (although the energy consumption with the latter was twice the amount of the former7). Other studies showed that an increase in exercise intensity increased the aerobic fitness. However, those who, in each workout, ran a 4-minute sprint 4 times, did not increase their aerobic fitness (VO2max) more than those who ran just one.8 Concerning strength training, some studies concluded that lower-load contractions were as good as higher loads, when lower-load training was compensated by an increase in the number of repetitions. Some found that increasing intensity could lead to modest improvements and that exercise to exhaustion had nothing to recommend it. As strength programmes traditionally last for 45-60 minutes, one can save time by exercising with near the maximum load. In addition, in several studies, one training day per week resulted in about the same increase in strength as 2 or 3 per week, shown both by our compilation and by others’ review.9 Increasing the number of sets of strength exercises did not always augment the training effect. One explanation might be the finding that lower extremities became stronger with 3 sets, while there was no difference between one and 3 sets for upper limb muscles.10 Perhaps it requires more to achieve a training effect on muscles that are in static, long-term, continuous use than on those in more phasic use. Training programmes often combine aerobic fitness or endurance and strength training. Even though development of high levels of endurance may prohibit development or maintenance of muscle mass and strength in trained athletes, this effect is probably less relevant for sedentary individuals. Some practical points, if one wants to design workouts that are compatible with everyday life: Home training may give as good results as group training in gyms. Isometric strength training can apparently provide as much of a gain in strength as concentric and eccentric training. Use of rubber bands or slings and one's own body as a counterweight, rather than dumbbells or barbells, can be effective. Planned variations of the weekly programme may be physiologically sound and boost motivation to continue training. A significant loss of aerobic fitness has been found after just 2 weeks without exercise.9 If, on the other hand, the intensity of aerobic fitness training remained stable, VO2max could last for 15 weeks, even though the training's frequency and duration were reduced to one-third. However, reduction of one or two-thirds of the intensity, with sustained frequency and duration of exercise, significantly reduced both VO2max and strength gains.9 To find out which type of exercise works best, blood-borne biomarkers for aerobic fitness and strength development would be desirable, so one did not have to wait for many weeks of training before being able to judge the results—results obtained after few weeks may be compounded by the spurious effect of increased adaptation to the testing procedure. To our knowledge, useful biomarkers are not yet available. In conclusion, one may lose little in aerobic fitness and strength if one practices an easier routine than the exercise programmes recommended by ACSM. We found that as little as a 20-minute exercise (vs ACSM's 20-60) twice a week (vs ACSM's 3-5) may be sufficient to develop and maintain satisfactory aerobic fitness, provided that the training is in, for example, 4-minute intervals with 85%-90% of maximum heart rate. For strength gain and maintenance, resistance training at 60%-70% of 1 RM, once a week (vs ACSM's 2-3), with one set (vs ACSM's 2-4) of 8 repetitions (vs ACSM's 8-12) per muscle group, appears to give satisfactory results for most sedentary adults. The authors declare no competing interests.