Being a successful endurance athlete usually is associated with an obsessive personality--not only do we worry about the quality of our workouts, we also are concerned by their quantity. A solid training program is based on the aggregation of component units into a season-long pattern, with the hope that the normal build-up of fitness coincides with our most important events. Most coaches will encourage their athletes to think of the big picture when it comes time to plan and execute daily workouts; we know intellectually that missing an occasional workout won't hurt us--in fact, we might benefit from an unscheduled day or two off--but emotionally the thought of deviating from a carefully structured training plan can cause us anxiety. This anxiety often manifests itself in stacking workouts--increasing the workload in the remaining sessions of a cycle to make up for missed time.
It's illustrative to think of the workloads that training places on our bodies from short and long-term perspectives. Not only do we need to gradually increase workload demands within a specific training cycle so that we adapt and grow stronger, we also must be mindful that workload stress accumulates over time. There are two concepts that help us better understand this phenomenon: acute training load; and chronic training load. If you want the scientific definition of these terms, do a simple Google search; for the purposes of this discussion, think of the acute training load (ATL) as the stresses that training places on the body for a relatively short period of time, such as one week. Chronic training load (CTL) tracks training stress over a much longer period of time (say, forty days) and across multiple training cycles. Graphing the relationship between these two variables helps us gain a sense of whether our fitness is improving; it also helps us place into context the potential impact that missing a workout might have on our ability to achieve our season's goals.
Below is a graph that displays approximately four months of training data. My training is based on a four week cycle: three weeks of build, and one week of recovery.
The blue line tracks my acute training load, a metric that measures the stresses over a seven day rolling period. The dips in the blue line represent recovery weeks; note that there is a dip in the middle of the second month's cycle, when I took two days off because I had the flu. Also note how the intensity of each monthly cycle has gradually increased since I began preseason training in November.
What's more important is the trending of the red line in the graph, which represents my chronic training load. The first month marked by the graph is very jagged; the chronic training load tracks exercise stress over a rolling forty day period and there wasn't enough data points in month one (November) to describe an accurate trend. But tracking the red CTL across multiple months describes a line the generally slopes upward, which means (to simplify considerably) that my fitness is gradually increasing, as signified by my ability to work at higher loads for more extended durations. As I continue to track my data for upcoming training cycles, I would assume that the CTL/red line will continue to trend upward until my first A priority event.
The math underneath the values that inform my training graph is beyond the scope of this specific article; for now, what I am trying to show is that it is important to consider daily workouts from a broad perspective and that missing an occasional workout won't have a negative impact on your overall preparation and performance.