Physical Activity in Adolescence

Position Statement

The Faculty of Sport and Exercise Medicine UK (FSEM) has analysed the evidence associated with the effects of physical activity (PA) during adolescence and developed evidence-informed recommendations for health-related physical activity (PA) in adolescents.

Physical Activity

In adolescents, high levels of sedentary behaviour such as time spent lying and sitting (e.g. playing electronic games) during waking hours are associated with poor health. In contrast, moderate-to-vigorous PA (MVPA) is associated with benefits to health and well-being. Moderate PA (MPA) is classified as at least 4 METS (4 x resting metabolic rate) which is broadly equivalent to brisk walking (i.e. heart rate [HR] of about 140 bpm or about 70% of HRmax). Vigorous PA (VPA) is defined as 7 METS (i.e. HR of about 160 bpm or 80% of HRmax) which is broadly equivalent to jogging.

Adolescent boys participate in more MPA than girls with the gender difference being more marked in comparisons of VPA. The PA of both genders declines as they move through adolescence. PA patterns are sporadic and sustained periods of MVPA are not part of the lifestyles of the majority of adolescents. Recent objective studies, which have collected data using accelerometry, indicate that less than 25% of adolescents accumulate an average of 60 min per day of MPA.

Cardiorespiratory Fitness (CRF)

Credible international norms for adolescent CRF are not available but CRF can be increased with appropriate exercise. Exercise at an intensity of 85-90% of HRmax (i.e. HR of 170-180 bpm), for 20-40 min, 3 times per week will induce 8-10% improvements in CRF within 8-12 weeks. Greater gains in CRF are likely if the exercise programme is sustained for longer than 12 weeks.

There is no compelling evidence to suggest that exercise-induced increases in CRF are influenced by gender, age, or maturity status. The CRF benefits of this type of constant intensity exercise (CIE) programme manifest themselves principally through an increase in maximal stroke volume and therefore enhanced oxygen delivery to the muscles (central factors).

Recent research has demonstrated the efficacy of high-intensity exercise (HIE) in improving adolescent CRF. HIE consists of short duration (20-30 s) exercise intervals at 90-95% HRmax interspersed with short (10-20 s) recovery periods. There are indications that HIE-induced changes in CRF are principally through increased oxygen utilisation in the muscles (peripheral factors) which suggests that a combination of HIE and CIE might optimise increases in CRF but more research is required to determine precise dose-response effects.

Obesity and Overweight

Active adolescents tend to have less fat than those with low levels of PA but increased PA in normal weight adolescents has little effect on body fatness. However with overweight and obese adolescents, MVPA 3-5 times per week, for 30-60 min has been shown to reduce both overall fatness and visceral adiposity. Evidence showing the efficacy of HIE in reducing body fat is accumulating but dose-response data are currently not available.

Cardiovascular and Metabolic Health

PA enhances adolescents’ cardiovascular and metabolic health. The positive effect may be mediated through increasing CRF and reducing body fatness. A precise dose-response pattern has not been established, but, taken together, research studies suggest that daily, MVPA for 60 min helps to maintain a healthy cardiovascular and type 2 diabetes risk profile. A body of evidence is emerging indicating that bouts of HIE may also be beneficial in promoting cardiovascular and metabolic health.

Muscle strength

Muscle strength can be improved through a range of semi-formal activities, including the use of body mass and external resistances, being incorporated into daily life. To optimise increases in muscle strength, a programme of developmentally appropriate and progressive resistance exercise 2 or 3 times per week, not on consecutive days, is recommended. Beginners, initially under supervision, should start with 8-12 repetitions, of 6-8 exercises, against a resistance of 50-70% of 1 repetition maximum (1RM). Improvements in strength of up to 40% can be expected within 12 weeks. There appear to be no gender differences in the efficacy of resistance exercise training. Further strength gains will result from progressive resistance exercise being sustained for a longer period than 12 weeks but increases in muscle strength gradually decay at a rate of about 3% per week if the exercise programme is stopped.

Skeletal Health

10 min of high impact, weight-bearing exercise (e.g. high-intensity jumping) supported by 40-50 min of general weight-bearing PA, on 2-3 days per week has been demonstrated to significantly increase bone mineral content. The pre- and early-pubertal (in girls, pre-menarche) years provide a ‘window of opportunity’ for the enhancement of bone mineral content through PA.

Mental health and well-being

Although the optimal prescription of PA is unclear, MVPA is associated with increases in self-concept and reductions in depression and anxiety. Positive effects of MVPA on classroom behaviour, cognitive performance and academic achievement have also been consistently reported.

Recommendations

The minimum and optimum doses of PA required to promote specific aspects of adolescents’ health and well-being are yet to be established and more rigorous dose-response studies are urgently required. However, the extant scientific evidence strongly supports the conclusions that:

i) MVPA reduces body fat and benefits cardiovascular, metabolic, and mental health and well-being.

ii) Resistance exercise enhances muscle strength and the ability to perform day-to-day tasks.

iii) High impact, weight-bearing PA promotes skeletal health at an optimum time to enhance bone mineral content. Few adolescents regularly experience the intensity and duration of PA associated with health-related outcomes.

The FSEM (UK) therefore recommends that adolescents should:

Accumulate an average of at least 60 min of MVPA per day including bouts of VPA of at least 5-10 min duration.

On 2-3 days per week include resistance exercise to enhance muscle strength and weight-bearing and other high impact PA to promote skeletal health.

Moreover, the FSEM (UK) recognises that these recommendations represent a minimum target and that regular high intensity exercise will provide additional benefits to adolescents’ health and well-being.

©Faculty of Sport and Exercise Medicine UK Physical Activity in Adolescents first published July 2014, reviewed March 2018, next review due March 2021.

Author: Professor Neil Armstrong

References:

Armstrong N, Van Mechelen W, editors. Oxford Textbook of Children’s Sport and Exercise Medicine. 3rd edition. Oxford, Oxford University Press, 2017, 225-409, 465-506.

Bond B, Weston KL, Williams CA, Barker AR. Perspectives on high-intensity interval exercise for health promotion in children and adolescents. Open Access Journal of Sports Medicine. 2017; 8: 243-265.

Janssen I, LeBlanc AG. Systematic review of the health benefits of physical activity and fitness in school-aged children and youth. International Journal of Behavioral Nutrition and Physical Activity. 2010; 7: 40.

Mountjoy M, editor. Sports: Keeping young people happy. British Journal of Sports Medicine. 2011; 45: 837-942.

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