Every runner has days when motivation is
missing and the legs feel like wet cement. Most of the
time, it’s just fatigue from training, work and
life piling up. But occasionally that “off day”
is something deeper—a sign you’re pushing
too far. A recent study on recreational runners, published
in the European Journal of Science and Sport, offers clues
on how to tell the difference between ordinary tiredness
and the early stages of overtraining.
The
study behind the findings
Researchers followed 24 runners through three phases:
three weeks of normal training, two weeks of heavy overload
and one week of recovery. They tracked both heart-rate
data (resting heart rate and heart-rate variability (HRV),
recorded at night) and subjective measures, such as soreness,
sleep quality and “readiness to train.”
When the intensity spiked
by roughly 80 per cent, half the group adapted and got
faster, while the rest hit a wall. Despite all the extra
work, their 3-km time trials slowed slightly—a state
known as functional overreaching. The combination of nighttime
heart rate, HR-effort index and readiness-to-train scores
correctly identified who was struggling with more than
90 per cent accuracy.
Elisabeth Scott, running coach and host of the podcast
Running Explained, says: “The study shows that both
heart data and how you feel are powerful indicators of
fatigue. Neither alone gives the full picture—but
together they can help you train smarter and avoid burnout.”
What happens when
you overreach
The runners who faltered not only felt sore, but their
bodies showed measurable stress. Average nighttime heart
rate rose about three per cent, while heart-rate variability
dropped. Sleep quality worsened and motivation plummeted.
Others, however, thrived under the same load, showing
lower heart rates and slightly improved HRV—proof
that recovery capacity is highly individual.
“Fatigue is personal,” Scott explains. “Two
runners can follow identical programs, and one will thrive
while the other crashes. It’s not about toughness;
it’s about how your system handles stress and recovery.”
Heart data meets real-world feelings
The heart doesn’t lie, but it can whisper instead
of shout. A single elevated reading isn’t a reason
to panic. What matters is the trend. If your resting heart
rate climbs for several days or HRV keeps dropping, you’re
likely not recovering fully. Low-tech signs are also important:
heavy legs, poor sleep, irritability or a sense of dread
before workouts. In the study, feelings of low readiness
and high soreness were among the first red flags. Listening
to those cues early can save weeks of frustration later.“Your
feelings are data. When motivation disappears or everything
feels harder than it should, your body is sending you
useful information,” says Scott.
Putting
the research into practice
You don’t need a sports lab to apply these findings.
Start by keeping a simple log that pairs your daily effort
level with how you actually feel. Write down your mood,
soreness and sleep, along with heart-rate or HRV data
if you track them. Over time, patterns start to emerge:
one tough day isn’t a problem, but when several
stack up, it’s a sign to ease off.
Building recovery into your
plan, such as an easy week every few cycles or rest days
before fatigue forces them, helps you stay consistent.
Pay attention to how your body responds to the same training
load. If your pace is steady but your heart rate keeps
climbing, that’s a cue you’re not bouncing
back.
Scott reminds her athletes,
“The goal isn’t to collect data—it’s
to understand yourself well enough to know when to push
and when to pull back.” A few mindful adjustments,
guided by both numbers and intuition, can make the difference
between steady progress and hitting the wall.
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