To lose fat, do you need strength training or is endurance training enough?
A combination of strength and endurance training makes sense. Strength training is intense and accordingly requires a lot of energy. It also raises the rate of muscle protein synthesis for up to 48 hours. This goes hand in hand with increased thermogenesis (heat production) and, as a result, a higher basal metabolic rate. Finally, strength training applied consistently over time leads to more muscle mass, which itself contributes to a higher basal metabolic rate. Strength training therefore has a threefold energetic effect on the energy balance and should be a fixed part of any training plan aimed at reducing fat mass.
What does calorie consumption fundamentally depend on?
Daily energy expenditure fundamentally depends on basal metabolic rate and activity-related expenditure. Basal metabolic rate is influenced by height and body mass, sex and age. Activity-related expenditure essentially depends on daily activity level, that is, how much physical activity someone does and at what intensity.
Why is exercise so important for weight loss? Surely eating fewer calories would be enough?
In principle, that's correct. If energy intake is reduced below the level of actual energy expenditure, the body essentially starts breaking itself down. But there's a problem with this self-breakdown: the goal is to break down fat. What usually gets broken down first, though, is muscle. This loss of muscle needs to be prevented with targeted training. What's more, the health benefits of exercise go far beyond the positive effect on body composition.
And people with a lot of muscle burn more fat than untrained people ...
People with a lot of muscle have a higher basal metabolic rate, because maintaining muscle costs energy. Strength training can raise muscle protein turnover for up to 72 hours after training, which goes hand in hand with increased energy expenditure. Whether this is durably linked to increased fat oxidation — colloquially also known as fat burning — has not yet been clearly established.
What type of training do you recommend in general?
A combination of endurance training and muscle-building training. With endurance training, fat is oxidised during the activity itself (more on this below). Muscle-building training — strength training, for example — raises the basal metabolic rate.
At what time of day is endurance training most effective?
If the goal is maximum fat oxidation during the session, then rather in the morning in a fasted state. At that point glycogen levels tend to be lower, which raises the fat-burning rate. That doesn't mean, though, that you'll automatically and visibly lose fat after a few training sessions. This also depends on energy intake, which in turn can itself be influenced by the same training, for example through changes in hormone and appetite regulation.
When it comes to the optimal endurance training to support body fat loss, three aspects need to be considered:
The total energy expenditure during training
is higher the more intense the workout is and the longer it lasts.
The amount of fat in grams that is oxidised — or "burned" — per minute of training,
is, contrary to the persistent myth, highest during relatively intense training. When cycling, that's at around 65 percent of maximum oxygen uptake, or roughly 75 percent of maximum heart rate. For anyone who wants to know exactly at which training intensity their fat oxidation rate peaks, specialised scientific tests are available commercially.
The durability of the rise in fat oxidation rate at 24 to 48 hours after exercise
is primarily determined by the total energy expenditure during the session. 24 hours after an endurance workout, on a bike for example, the fat oxidation rate is still slightly elevated. This happens regardless of whether someone trained for 60 minutes at 65 percent of maximum oxygen uptake or for 90 minutes at 45 percent of maximum oxygen uptake. For averagely well-trained young men, both examples work out to around 700 kcal (2.93 MJ*); for women, because of their lower absolute physical capacity, it's around 440 kcal (1.67 MJ). Regardless of training intensity, women appear to mobilise more energy from fat relative to total energy expenditure during training (about + 15 percent) than men do. However, in women the effect of an elevated fat oxidation rate has almost disappeared after 24 hours and is completely gone after 48 hours. In men, by contrast, the effect persists for up to 48 hours after training. Finally, people with a good level of endurance fitness can mobilise more energy from fat during training.
For all these reasons, and also for reasons of time and practicality, it's worth moving away from "homeopathic" intensities in endurance training too and training intensely instead. Interval programmes are well suited to this. Four-minute intense blocks at a minimum of 65 percent of maximum oxygen uptake, alternated with one- to three-minute easier blocks (for example at 45 percent of maximum oxygen uptake), are recommended. The session should last between 30 and 60 minutes.
* MJ = megajoule: the amount of energy released during combustion.
