Testing and prescription

According to the WHO 2020 guidelines, aerobic PA performed at moderate and vigorous intensities refers to any bodily movement involving large muscles performed at an intensity between 3 to <6 and ≥6 times the resting energy equivalent expended (metabolic equivalent of tasks; METs), respectively.1 This categorisation is useful for providing overall recommendations; however, it has some limitations when categorising PA at relative intensities based on fixed METs, as it does not account for individual differences in fitness level, body mass, age and sex, among other factors.11 12 Further, exercising at a fixed MET or relative percentage of maximal oxygen uptake (V̇O_2max) is not optimal because, in some cases (ie, poor fitness levels), performing moderate to vigorous-intensity exercises (ie, ~6 METs) represents intensities close to V̇O_2max,11 generating different levels of cardiac and metabolic demands13 14 that could lead to discomfort and higher unplanned stress. Therefore, it is advocated to associate moderate and vigorous-intensity exercises with individualised homeostatic disturbances, such as ventilatory or lactate thresholds 1 and 2 (VT1, VT2, LT1 and LT2, respectively),15 and thus we suggest including these definitions in future guidelines for aerobic exercise prescription at the individual level in populations with different health conditions. However, we recognise that these fitness assessments are usually not available or easy to understand for the general population, so it is essential to provide tools that are accessible to everyone. Nonetheless, we emphasise the importance of educating the general population about their fitness level, PE testing and prescription, as well as having access to assessments in healthcare or training centres.

In line with the above, a positive addition to the WHO 2020 guidelines is the use of the rating scale of perceived exertion (RPE) in the definitions of PE intensity. A study conducted on 2560 subjects (13–83 years old), including both sexes and different fitness statuses, showed that during incremental aerobic exercise tests, the mean values for LT1 and LT2 were closely associated with an RPE (6–20 Borg’s scale) of ~10.8 and ~13.6, respectively.16 Similarly, during a progressive aerobic exercise test, RPE values of ~4.3 and ~6.5 (0–10 scale) corresponded to blood lactate (BLa) levels of 2 and 4 mmol/L, respectively.17 Importantly, this approach is not only limited to traditional aerobic exercise modalities like walking, running or cycling but also to effective and recently evaluated outdoor fitness equipment (OFE) exercises (ie, air walker and ski machine),18 where low, moderate and high RPE values can be achieved by manipulating the cadence of movement19 and consequently regulate exercise intensity. Moreover, the use of RPE for intensity distribution allows to determine specific training zones for aerobic exercise testing and prescription, consistent with the typical three-intensity zone model used by endurance athletes (zone 1 (Z1): <LT1/VT1; zone 2 (Z2): ≥LT1/VT1 up to ≤LT2/VT2; zone 3 (Z3): >LT2/VT2),20 21 and its use should continue to be recommended. However, because the RPE in subjects with health complications shows only a good agreement with BLa concentrations at low-intensity exercise,22 we suggest caution when professionals prescribe moderate and high-intensity exercises based on RPE in these populations.

To reinforce future guidelines, we also suggest the incorporation of the ‘Talk Test’ (TT) as a simple way to regulate PE intensity.23 The TT asks the participants how comfortable they feel speaking during exercise, and its use has been associated with low (≤2 mmol/L; speaking comfortably), moderate (~3–4 mmol/L; not speaking comfortably) and high (>5 mmol/L; unable to speak comfortably) levels of BLa during continuous aerobic type exercise, and has a close relationship with RPE24 and VT1 or gas exchange threshold.25 Moreover, the use of the TT can be extended to different populations, including cardiac patients,26 overweight and obese people27 and elite athletes,28 where the use of an analogue scale can strengthen this approach.27 However, it is important to highlight that the RPE and TT must be approached individually according to the type of exercise prescribed. In support of the use of the RPE and TT, recently Bok et al reported that both instruments are reliable and valid measures for the demarcation of ventilatory and lactate thresholds and can be used to elicit homeostatic disturbances associated with moderate, heavy and severe-intensity domains during continuous exercise.29 Therefore, the TT could be added as another practical and inexpensive method for professionals to determine specific training zones for aerobic exercise testing and prescription in a simple and fairly accurate manner. In a practical way, professionals can recommend for people to talk with others or simply repeat a standardised sentence during the exercise session and thus easily know at what intensity zone they are exercising.

Programming

Notably, one aspect of the WHO 2020 guidelines that we believe could be further complemented relates to aerobic exercise programming. Even though it is mentioned that ‘many of the benefits of physical activity are observed within average weekly volumes of 150–300 min of moderate-intensity or 75–150 min of vigorous-intensity, or an equivalent combination of moderate-to-vigorous physical activity’, we consider that the current recommendations may be more precise for exercise programming by adding a fundamental aspect, which is the training intensity distribution (TID), and not only total amounts of weekly PA. Olympic medallists in endurance and mixed sports,30 and elite athletes live longer than the general population and have a lower risk of mortality, cardiovascular disease and cancer.31 Interestingly, endurance athletes typically adopt a TID programme where ~80% of the training volume is performed at low-intensity (ie, <LT1/VT1) and the remainder (~20%) at moderate to high-intensity (ie, ≥LT1/VT1) under a pyramidal (Z1>Z2>Z3) or polarised (Z1>Z3>Z2) model with a hard day-easy day approach.20 32 33 Although athletes perform higher training volumes (hours/week; km/week) than untrained individuals,34 we think that the use of the TID model in the general population could be a promising approach. Notably, recent evidence shows that in overweight/obese women (21±2 years, body mass index 32±3 kg/m²), a combination of high-intensity interval training (HIIT; 90% V̇O_2peak) and moderate-intensity continuous endurance training (MICT; 95% VT1) in a polarised intra-session volume distribution, similar to the TID model used by athletes, is a more effective exercise regimen compared with HIIT or MICT alone, for improving cardiorespiratory fitness and to counteract the cardiometabolic risks associated with overweight and obesity.35 According to current guidelines, MICT (low-intensity training in the three-zone model)20 can be prescribed in bouts of any duration,1 yet longer continuous bouts of 10 min or more may be more beneficial.36 37 Regarding interval training during moderate-intensity to high-intensity exercise, we recently proposed that long intervals (ie, ≥1 to 2 min) with ≥1 min recovery period should be prescribed for greater adaptations.38 Certainly, more evidence is needed regarding aerobic exercise programming and the use of the TID model in physically inactive subjects or with health complications; however, we believe it is essential to include more details regarding aerobic exercise programming in future WHO guidelines.

In summary, the use of the RPE for intensity distribution is a strength of the current WHO guidelines for aerobic exercise prescription; however, we believe that incorporating other simple and practical tools available to the general population for monitoring intensity, such as the TT, is warranted, as it provides greater specificity for aerobic exercise testing and prescription by professionals. In addition, we suggest incorporating the TID model used by athletes for aerobic exercise programming in the general population and physically inactive subjects, which typically involves continuous (Z1 and Z2) and interval (Z2 and Z3) aerobic exercise.21 32 33 From a practical perspective, people should first determine their aerobic training zones using the RPE scale and/or the TT and then translate this information to an aerobic exercise programme according to the goal of the TID model. For instance, if a person wants to exercise at low-intensity (Z1), they should feel ~3 on the RPE scale of 0–10 and/or be able to sing their favourite song; likewise, an RPE value >4 and/or not being able to sing their favourite song is a good indicator that a person is exercising at moderate-intensity to high-intensity (Z2 and Z3). According to the typical TID of athletes, improvements are observed after 6–8 weeks,39 40 therefore, we suggest testing with a similar periodicity. Figure 1 shows our approach to the continuum between aerobic exercise testing and prescription concerning these simple and practical tools.

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Figure 1

General diagram for testing and prescribing an aerobic exercise programme for the general population. (A) The diagnosis (test) of the current state (1) is the first step for the prescription of aerobic exercise by training zones based on simple and practical tools (2). (B) After determining the training goal (1), the training intensity distribution is applied under the pyramidal (zone 1>zone 2>zone 3) or polarised (zone 1>zone 3>zone 2) model format (2). For further details, refer to the text. LT, lactate threshold; RPE, rating scale of perceived exertion; RPE 0–10, rating scale of perceived exertion from 0 to 10; RPE 6–20, rating scale of perceived exertion from 6 to 20; TT, Talk Test; VT, ventilatory threshold; zone 1, exercise intensity <LT1/VT1; zone 2, exercise intensity ≥LT1/VT1 up to ≤LT2/VT2; zone 3, exercise intensity >LT2/VT2.

Testing and prescription

The WHO 2020 guidelines have emphasised the importance of strengthening or resistance exercise (RE) for enhancing overall health. However, the recommendation may be too broad when transferring this to testing and prescription. It only proposes that ‘additional health benefits will occur through participation in muscle-strengthening activities at moderate or greater intensity on two or more days a week’. Typically, the objectives and methodology of RE have been associated with neural and morphological effects,41 where the prescription of RE intensities is strictly linked to the load in relative terms.42 However, from a contemporary view, the ultimate goal of a resistance training programme is to improve the maximal force production applied against a specific absolute load(s) (mass).43 44 Regardless, it is essential to determine the magnitude of the external or absolute load before prescribing RE. The most traditional way to assess dynamic strength, although stressful and more likely to cause injury, is by setting how much weight an individual can lift for one-repetition maximum (ie, 1RM),45 where the most used indicator of intensity for RE prescription is the percentage associated with the 1RM (ie, %1RM).46 However, a safer and popular way to assess strength is by using submaximal loads and counting the number of repetitions to fatigue (ie, nRM), relating this to a %1RM.45 Although these procedures are simple and practical, they have their limitations. For instance, to achieve a true 1RM, traditional multi-joint strength exercises must reach a specific movement velocity (MV) that characterises them,47–49 so if this is not achieved, it is not possible to speak of a true 1RM. Regarding the nRM, the number of repetitions performed between 50% and 85% 1RM shows a large inter-individual variability (~20%) with bench press exercise,50 so if two individuals train with the same number of maximum repetitions, they may be training at a different %1RM. That being said, the nRM test can be used as a practical tool to individually determine an absolute load (kg) for RE prescription, as recently reported in older adults and master athletes.51 Furthermore, as moderate-load multi-joint REs of the upper and lower limbs (ie, 65%–75% 1RM) have a range of ~10 to 20 nRM,52 we suggest using the nRM within the 10–20 repetition range to assess moderate loads (kg), where a higher or lower nRM will robustly represent light and heavy loads, respectively.

Recent evidence has reported that traditional multi-joint strength exercises have a very high relationship between MV and %1RM,47–49 allowing with few submaximal loads to estimate 1RM, reducing the risk of injury and the variability of applying nRM. Furthermore, control of MV allows assessing the velocity loss (VL), with the latter being associated with the level of effort (LoE) in relation to the repetitions in reserve (RIR) and to the percentage of repetitions performed for the maximum possible (%rep).52 Therefore, monitoring MV and VL during RE allows a precise knowledge of %1RM without the need to perform any 1RM or nRM test43 and to quantify neuromuscular fatigue objectively.53 However, measuring MV and VL requires specialised instruments (ie, transducers or validated mobile applications); therefore, we again propose using the RPE scale, as it validly measures exercise intensity and physiological exertion during RE.54 55 For example, the RPE (0–10 scale) in experienced and novice subjects has been reported to be a valid indicator for estimating %1RM and RIR at moderate-loads to high-loads, where an RPE of 1–2, 5–6 or 10, represented little to no effort, more repetitions can be performed or no more repetitions (max effort), respectively.56 Besides the RPE, the LoE approach, which is the relationship between the number of repetitions that are done in a set and those that could be done53 can also be used for prescribing RE. Interestingly, the LoE approach can be applied with traditional multi-joint exercises, relative intensities and in subjects with different strength levels.52

In an integrative and practical way, despite nRM (ie, exercise to failure) being suboptimal for RE prescription,57 58 it can be applied as a simple test to assess dynamic strength at moderate to heavy loads.51 Therefore, if a subject performs ~16 nRM at a specific absolute load (kg) and plans to train at a low to moderate LoE, it would be recommended to prescribe ≤8 repetitions (ie, 5–8 (16)) with an RPE value of 5–6 (0–10 scale). As a general rule, 3–4 sets should be performed with 2–4 min of intra-set recovery.49 59

Programming

Concerning RE programming, the WHO 2020 guidelines, as stated before, only refer to performing two or more days per week of muscle-strengthening activities. Again, although this approach has solid evidence,60 we consider it too general for RE programming. Greater upper-body and lower-body muscular strength levels are associated with a lower mortality risk in the adult population.61 Furthermore, greater muscular strength is associated with enhanced force-time characteristics, general and specific sport skill performance, enhanced potentiation effects and decreased injury rates.62 Just as athletes may have specific strength requirements,63 physically inactive or untrained subjects can also benefit from RE in its different manifestations (ie, light, moderate and heavy loads) according to their daily tasks and needs (work, leisure, housework, etc). For instance, a recent within-subject study in older adults observed that heavy loads were more appropriate for developing high-force capabilities. In contrast, using light loads was superior in promoting rate of force development, even though both protocols led to similar gains in power and muscle size.64 These results imply that it is possible to choose a variety of intensities for RE programming, which not only yield different adaptations but could positively affect participant enjoyment and adherence, avoiding training monotony.

Again, we want to highlight the role of VL and RPE for optimal RE programming. Low to moderate VL thresholds (≤25%) are superior for promoting strength, possibly by minimising acute neuromuscular fatigue while maximising chronic neuromuscular adaptations, whereas moderate to high VL thresholds (>20%–25%) are superior for promoting hypertrophy.65 These VL-based effects have been evidenced with upper and lower multi-joint exercises using moderate to heavy loads in healthy young adults66 67 and moderate loads in older adults.68 Recently Varela-Olalla et al found a high positive relationship between %rep and RPE and VL, where >50% rep was associated with >6 RPE (0–10 scale) and with >30% VL during the concentric action at the maximum possible velocity of a moderate to heavy load bench press exercise, allowing to quantify the LoE objectively.69 Similar results were found using the RIR-based RPE approach during heavy-load lower limb exercises.70 Although caution should be taken when relationships are considered, RPE is a valuable tool for estimating the LoE without having to measure MV, where the higher the RPE, the greater the LoE (ie, VL, %rep and RIR), independent of %1RM.

A relevant aspect to optimise RE adaptations is the concentric velocity at which the load is lifted. Repetitions performed at maximal intended velocity during the concentric phase have a more beneficial effect on dynamic neuromuscular performance than those performed at an intentionally slower half-velocity.71 Therefore, we suggest that the concentric phase of each exercise should be performed at the fastest possible velocity, according to the individual capacity. Thus, to achieve the maximum possible velocity against a specific absolute load, the applied force must be the maximum that the subject can exert against that particular load.43 However, we understand that for learning reasons, subjects could be asked to perform at a controlled velocity during the programme’s initial phase. In this case, the use of RPE to control the LoE can also be extended to multi-joint72 and single-joint73 exercises performed at a controlled velocity.

Finally, we know that not everyone has access to training centres. In this context, it is interesting to highlight that public OFEs (ie, rowing machine; bonny rider) are also effective for the improvement of muscle strength18; where low, moderate and high RPE values are achieved by manipulating the cadence of movement19 and consequently regulating the LoE. Furthermore, the RPE scale has been used to determine the stress imposed on all-out body-weight (ie, callisthenics) and elastic band (grip-related tension) exercises.74 75 This last element suggests an exciting alternative for subjects with muscular weakness or sarcopenia. In this regard, Colado et al have validated an OMNI-Resistance Exercise Scale (0–10; extremely easy to extremely hard) with elastic band RE in older adults.75 However, despite the attractiveness of these tools, it is essential to point out the difficulty of determining the force manifestations (light, moderate and heavy loads) with them, where a velocity-effort (eg, load, %RM) relationship might not be the primary RT training goal.44

In summary, although nRM is not an optimal training methodology, it is a simple and practical individual testing tool for muscle-strengthening exercises and is within reach of the general population. For the prescription and programming of RE, the VL estimated through RPE and %rep (or LoE, RIR) allows to project the desired effects of the training programme. From a practical perspective, once the muscle-strengthening exercises are chosen, the subject can determine the absolute load (kg) through nRM testing and prescribe each exercise considering the RPE scale and/or the %rep (or LoE, RIR). This information is then transferred to an RE programme based on the daily force application needs (ie, light, moderate or heavy load). Thus, if a subject performs ~10 nRM (ie, moderate load) of a strength exercise and wants to maximise neuromuscular adaptations, he/she could prescribe ≤5 repetitions (ie, 3–5 (10)) at a fast concentric velocity reaching low to moderate RPE values (ie, ≤6 RPE; 0–10 scale). On the other hand, if the goal of the person is to maximise structural adaptations (ie, hypertrophy) at the same moderate load, >6 repetitions (ie, 8–9 (10)) should be performed, reaching moderate to high RPE values and %rep (high LoE; lower RIR) (ie, ~8+ RPE; 0–10 scale). According to previous studies,49 59 we suggest 3–4 sets with 2–4 min of recovery between them. In agreement with the observed changes in the load–velocity relationship,66 71 we suggest to adjust the load every 6–8 weeks by performing a new nRM test. Although with certain limitations, this approach can also be applied with OFE, body-weight (callisthenics) and elastic band exercises. Figure 2 summarises our approach regarding RE programming based on VL with simple and practical tools (ie, RPE and %rep) depending on the objectives pursued.

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Figure 2

General diagram for testing and prescribing a resistance exercise programme for the general population. (A) The diagnosis (test) of the current state (1) is the first step for the prescription of resistance exercise through percentages of repetitions with respect to the maximum possible (ie, nRM) to then determine the intra-set velocity loss at different external loads (kg) based on simple and practical tools (2). (B) Once the training goal has been established (1), the intra-set velocity loss is planned through the percentage of repetitions with respect to the maximum possible and the rating scale of perceived exertion (RPE) (2). For further details, refer to the text. Fast MV, fast movement velocity (concentric phase); LoE, level of effort; nRM, repetitions with respect to the maximum possible; %rep, percentage of repetitions with respect to the maximum possible; RPE, rating scale of perceived exertion; RPE 0–10, rating scale of perceived exertion from 0 to 10; RIR, repetitions in reserve; VL, velocity loss.

Conclusions and perspectives

In the present article, we propose that current reference guidelines on PA for the general population from the WHO may be moved forward by adding specific recommendations for exercise prescription in apparently healthy individuals or those with different health conditions. The research in the field of PA during the last decades has set an opportunity for providing overall recommendations based on high-quality evidence. Further efforts should focus on providing complementary and more specific recommendations. In the meantime, we propose a methodology in which the prescription of aerobic exercise should be based on individualised metabolic disturbances and the TID model used by endurance athletes. For RE prescription, we suggest that loads based on MV associated with VL are a more reliable approach than a fixed set number of repetitions. In both cases, the RPE scale can be a useful and valid tool for aerobic and RE testing and prescription. In addition, for aerobic exercise prescription, the TT could be added to provide additional support. These simple tools will allow the general population to be educated about their fitness level and self-management of exercise intensity, and aid professionals, clinicians and primary care providers to optimise exercise programmes for improvement of fitness status, and exercise adherence without the need for specialised equipment and measurements. To improve the specificity of exercise adaptation, future research should focus on further developing training programme components for the general population, such as exercise frequency, intensity, time and type (ie, the FITT principle).