The big issue around long distance and long duration events is the orders of magnitude of the damage and therefore subsequent recovery.
In specific Ironman Triathlon research , various blood biomarkers of inflammation were tested 1, 5 and 19 days post event. The research concluded that although in the acute phase of recovery (1-5 days post event) much of the inflammatory markers withdrew, there was still a low grade systemic inflammation beyond this point, suggesting complete recovery takes beyond a week.
To further enhance our knowledge of the topic, research from 2017 suggests there may be a sex-difference in the tolerance of mechanical stress associated with endurance running . Researchers involved with the study said “we saw high values of myoglobin, CK and AST. This ‘cluster’ is related to the breakdown of skeletal muscle”, but this cluster was in lower levels in the female athletes. An explanation for this could be in that oestrogen protects against muscle damage and is naturally higher in women.
The nutritional aspects of recovery have to be taken into account as well. Although athletes competing in extreme endurance events will fuel throughout the event, the reality is the sheer energy expenditure will result in weight loss.
In a single-person study on an endurance cyclist, various biomarkers and anthropometric data points were assessed . The event consisted of 2,272 km distance covered across 5 days. Despite the athlete consuming nearly 40,000 calories during the 5 days, his energy expenditure was measured at over 54,000 calories and he subsequently lost nearly 2kg in weight. This was from an already very lean, endurance-trained man so arguably it’s more impactful.