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08. Exercise, Muscle and Metabolism: Aerobic and Strength Training
Walking, cycling and strength training provide different stimuli for the body. Their value, however, cannot be reduced to the calories displayed on a watch.
In this article, we compare aerobic and resistance training, look at research on blood glucose and explain what short-term changes in GLP‑1 after exercise mean.
Aerobic and resistance training: what is the difference?
Aerobic activity
Examples include brisk walking, cycling, swimming and running. At sufficient intensity, it increases breathing and heart rate and develops cardiorespiratory fitness. [1, 2]
Resistance training
This involves muscles working against resistance. It may use weights, machines, resistance bands or suitable bodyweight exercises. Strengthening the major muscle groups is a separate component of physical activity recommendations. [1, 2]
Isometric exercise
The muscle produces tension without visible joint movement. Examples include holding a forearm plank or gently pressing your palms together. This can build strength in the position you practise and help with stability. Breathe steadily and avoid maximal effort. If you have high blood pressure or a heart condition, discuss suitable intensity with your doctor. [7]
Stretching
Stretching helps maintain flexibility and range of motion. After warming up, hold a stretch for around 10 to 30 seconds and breathe steadily. Avoid bouncing or stretching into pain. [8]
These activities complement each other. The choice need not be “cardio or weights”, but an appropriate combination based on a person's circumstances and goals.
Muscles and metabolism: what is useful to track?
When assessing training, it is also useful to consider strength, endurance and the ability to manage everyday activities. Body weight alone does not capture all the reasons regular activity is recommended. The WHO describes benefits for both physical and mental health. [1]
It is equally inappropriate to promise that every kilogram of muscle will “dramatically speed up metabolism”. Such a claim requires specific measurements and cannot replace an assessment of the overall routine.
Endurance and weight loss
Start with an easy walk and gradually increase the time or pace. Choose an effort you can sustain and return to regularly. [1, 5]
A meta-analysis of 116 randomised trials involving 6,880 adults with overweight or obesity linked more weekly aerobic exercise to larger average reductions in weight and waist circumference. The findings mainly concern moderate to vigorous activity. [11]
Blood, oxygen and endurance
Haemoglobin in red blood cells picks up oxygen in the lungs and releases it in tissues. Endurance also depends on cardiac output, blood flow through small vessels and how well the muscles use oxygen. [10]
Blood photobiomodulation in the Raggi and Vallesi study
The researchers followed four male bodybuilders. After ten sessions of intravenous laser blood irradiation with red and green light, the average time spent skipping rope before fatigue increased by 83.33%. The maximum bench press load rose from 89.5 to 99.75 kg, an increase of 11.45%. [9]
The skipping-rope result was still above baseline after 16 weeks and had returned to baseline on average after 20 weeks. The study had no control group and did not directly measure blood cell function or oxygen transport. Whether the method could help people maintain moderate activity or lose weight remains an open question. [9]
What did a study in type 2 diabetes show?
The randomised HART‑D trial included 262 previously inactive adults with type 2 diabetes. Over nine months, it compared aerobic training, resistance training, their combination and a control group. [3]
Combined training significantly improved HbA1c compared with the control group. HbA1c is an indicator of longer-term blood glucose levels. The aerobic-only and resistance-only groups in this particular trial did not achieve a statistically significant difference in HbA1c compared with the control group.
This does not mean that walking or strength training alone has no value. The result concerns a specific measure and training programme. Moreover, this was supervised exercise in people with diabetes, not a universal promise of results for everyone.
Exercise and GLP‑1: a short-term response
In a human study published in 2017, researchers measured appetite, food intake and hormones after aerobic exercise. Exercise briefly reduced appetite ratings and increased GLP‑1 and PYY levels. However, energy intake at the observed freely eaten meal did not differ significantly between the exercise and control conditions. [4]
The result shows why hormones, subjective hunger and actual food intake need to be distinguished. A short-term increase in GLP‑1 after training does not demonstrate lasting hunger suppression or an effect comparable to a medicine.
A single exercise session and long-term training are different questions. An experiment following the hours after exercise does not automatically predict changes in weight over months.
An overview of activities and expectations
| Activity | Example | How should it be viewed? |
|---|---|---|
| Aerobic | Brisk walking, swimming, cycling. | Part of developing cardiorespiratory fitness and weekly physical activity. |
| Resistance | Weights, resistance bands, bodyweight exercises. | Works the major muscle groups and complements aerobic activity. |
| Movement throughout the day | Walking for transport, taking the stairs, breaking up sitting. | Helps incorporate more activity into a daily routine. |
| Combined routine | Regular walking and two days of strength training. | Combines different activity stimuli; it does not guarantee a specific amount of weight loss. |
How much activity does the WHO recommend?
For adults, the WHO recommends 150 to 300 minutes of moderate-intensity aerobic activity or 75 to 150 minutes of vigorous-intensity activity per week, or an equivalent combination. This also includes strengthening the major muscle groups on at least two days a week. [1]
These are general health recommendations, not an individual weight-loss plan. Some activity is better than none; when starting from low activity levels, gradually increasing the workload makes sense.
What could a simple week look like?
One example provided by the CDC is five 30-minute brisk walks per week and two days of muscle-strengthening activity. Aerobic activity can also be divided into shorter periods. [2]
Such an example should be adapted to fitness, health status and recovery. After prolonged inactivity or with health limitations, discuss the choice and intensity of activity with a healthcare professional. [5]
Frequently asked questions
Do I have to run for activity to count?
No. Brisk walking is also an aerobic activity. Movement can be incorporated into transport, leisure time or everyday tasks. [1, 2]
Is resistance training alone enough?
The recommendations include both aerobic and muscle-strengthening activity. They complement each other, and one does not automatically replace the other. [1]
Does training increase GLP‑1?
The cited experiment recorded a short-term increase after aerobic exercise. This does not mean the same response occurs after every type of training or in every person. [4]
Why might I not lose weight after exercising?
Neither a short-term hormonal response nor a single session predicts long-term weight changes. Exercise also matters in areas that the scales do not show.
Can exercise replace diabetes treatment?
The cited study does not make that recommendation. Activity is part of care, but do not stop or adjust medicines on your own. [3]
Simply put
Choose a mix of activities you can do regularly. Aerobic exercise builds endurance, strength training including isometrics builds strength, and stretching supports flexibility. Notice what you can do more easily in daily life. [1, 7, 8]
Next article 09: Insulin resistance and blood glucose — what they mean and how they are assessed.
Continue to article 09: Insulin resistance and blood glucose →Curious about what’s in food supplements?
Compare ingredients, amounts per daily dose and precautions for use.
Findings from intravenous blood irradiation cannot be generalised to non-invasive wellness devices.
Educational purpose: This article does not replace an individual training plan, medical assessment or treatment. If you have an illness, injury or movement limitation, adapt activity to the advice of a healthcare professional.
