Life is full of risk – from the dangers posed by a famished hunter that may be lurking in the shadows to the challenge of negotiating an unpredictable environment – and some animals are simply better at dealing with risk than others. These bold creatures seem more content to explore unfamiliar situations than other, timid creatures that would prefer just to hide. However, Frank Seebacher and his colleagues Alexander Little and Rob James were curious to determine how much of an impact the muscles that give an animal strength might have on their courage. ‘Locomotor performance is determined to a large extent by energy metabolism and muscle function’, Seebacher says, so the team decided to find out how the strength of zebrafish muscle contractions affects their boldness.

The team first exposed fish to a drug (nifedipine) that reduces the strength of muscle contractions and then filmed the animals as they explored a new territory and an unfamiliar object, assessing the fish's boldness and swimming performance as they became weaker. They then directly measured the strength of each fish's muscular contractions before investigating the contribution of muscle function to the animals’ audacity.

Combining various muscle contraction characteristics and analysing the impact of this ‘muscle factor’ on the fish's swimming performance, the trio showed that muscle contraction has a major impact on the animal's activity levels and that activity, in turn, also significantly influenced their boldness. So muscle contraction does contribute to an animal's boldness, and Seebacher and colleagues suggest that an animals’ boldness may simply reflect how fast it can swim, with faster fish appearing bolder simply because they move farther than slower fish, providing them with greater opportunities for exploration.

Seebacher
,
F.
,
Little
,
A. G.
and
James
,
R. S.
(
2015
).
Skeletal muscle contractile function predicts activity and behaviour in zebrafish
.
J. Exp. Biol.
218
,
3878
-
3884
.