The term “metabolic conditioning” or METCON is an unfortunately vague term. Frequently, when two people are speaking about METCON, they are thinking about completely different concepts. Generally (and this is not always true) what is meant by METCON is a training session that is high intensity and results in a heart rate in zone 4 or 5 (in the 5 zone system we discussed earlier). There are three important facts to know about METCON. The first concerns the sites of physiological adaption (physical changes due to training). The second concerns transfer of training effects and the third concerns the adaptation timeline (how fast fitness develops).
Although the reality is a bit more complex, it is useful to think of there being two adaptation sites for METCON training, central and peripheral. The primary central adaptations are cardiovascular. The heart becomes stronger (greater stroke volume). There are also some hormonal changes. The peripheral changes occur in the specific muscles that are in use during the METCON. Only the muscles that are recruited and used adapt. Furthermore, some muscles are used to a much greater extent, so they adapt more. Think of a METCON exercise like the “thruster.” The biceps are used a little, but not nearly as much as the deltoids and gluteus (if you are doing it right!), so the biceps will not adapt much to that exercise. There is a specific pattern of adaptation that depends on how much specific muscles were recruited, how long they were used, and the pattern of use (i.e., intervals, or on/off cycles). This makes the peripheral adaptations very mode specific (mode refers to the type of exercise used.). The central adaptations are very general and the peripheral adaptations are very specific.
This brings us to the concept of the transfer of training effects. Does one METCON exercise make you better at another METCON exercise, or a real life challenge? The central adaptations have a high degree of transfer. After all, it is the same cardiovascular system being used no matter what exercise is performed. So the improvement in cardiovascular capacity is expected to result in improvements across a wide range of training and life challenges. However, the peripheral adaptations are very mode specific. There is little transfer from one exercise or mode to another. The transfer effect is proportional to the extent of overlap in muscles used. Even if there is lots of overlap in muscles used, there may be little training transfer because the weak link muscles may be different. For example, an athlete may have done tons of “thrusters” but when they transition to “sumo deadlift high pull” they may find that they can’t do many because their grip gives out. Grip strength is not trained significantly with “thrusters.”
The real issue here is that most of the training effect is peripheral, not central. Central adaptations account for only a small part of the training effect. Therefore, the concept of improving general work capacity is a flawed one. There really is not “general” work capacity. If I want to improve a wrestler’s work capacity do I have him swing a sledge hammer and row a Concept 2, or do I have them grapple? Specificity matters, a lot. Everyone knows that strength is mode specific. A big bench press does not necessarily mean you have a big squat. However, other fitness modes are very mode specific as well (i.e., METCON, endurance, flexibility). Exercise programming should take this into consideration. METCON, if needed at all, should closely mimic known job demands. Where job demands are unknown but likely to be intense, METCON should focus on movements that are most likely to be encountered such a gripping, pulling, lifting, throwing etc.
The third important fact about METCON is that fitness adaptations happen quickly. Anyone who has trained and measured METCON performance knows that significant improvements can happen after only 2-3 specific METCON workouts. What you may not know is that although results happen quickly, they plateau quickly as well. Three to 6 weeks can get an athlete very close to their max METCON performance at their current level of strength. METCON fitness is built quickly. This is good news and bad news. Athletes can expect big improvements quickly. However, pretty quickly results will taper off with little improvement to follow unless they get stronger. This has programing implications. Doing METCON year round, or starting it too early may be a mistake. If you are training for a specific school, selection or deployment, you may be better served by saving your METCON training for the last couple of months prior, and focusing on fitness qualities that take a long time to develop in the months or years prior to that (i.e., strength and hypertrophy). Also, METCON incurs a high recovery cost and can directly interfere with strength and hypertrophy gains. Both are very important considerations that are rarely discussed. Depending on the athlete’s goals, it may make sense to minimize METCON training until it is needed.
