diff --git a/tests/cardio_test.cpp b/tests/cardio_test.cpp
index 8cea45d59aaf9..d62e1c4e2b18c 100644
--- a/tests/cardio_test.cpp
+++ b/tests/cardio_test.cpp
@@ -74,6 +74,21 @@ static int running_turns( Character &they )
 //   + 10 * [ Athletics skill ]
 //
 // For NPCs (having no cardio), the formula is simply 2 * BMR.
+
+
+// Trait Modifiers
+// ---------------
+// There are at least two ways mutations/traits can influence cardio fitness level:
+//
+// - Using "cardio_multiplier" to affect cardio level directly
+// - Affecting total body size, which affects base BMR and thus cardio
+//
+// Being SMALL or having a trait with cardio_multiplier less than 1 reduces cardio,
+// meaning Tiny, Little, and Languorous characters cannot run as far.
+//
+// Conversely, being LARGE or having cardio_multiplier greater than 1 increases cardio,
+// meaning Inconveniently Large, Freakishly Huge, Indefatigable, and Hyperactive
+// characters can run longer before their stamina gives out.
 //
 TEST_CASE( "traits affecting cardio fitness level", "[cardio][fitness][traits]" )
 {
@@ -166,48 +181,82 @@ TEST_CASE( "traits affecting cardio fitness level", "[cardio][fitness][traits]"
     // Body size affects BMR, which in turn affects cardio fitness and stamina
     SECTION( "smaller or larger body size from mutation" ) {
         // Tiny (SMALL2)
-        GIVEN( "small body size" ) {
+        GIVEN( "Tiny (SMALL2) body size" ) {
             set_single_trait( they, "SMALL2" );
             REQUIRE( they.get_size() == creature_size::tiny );
             REQUIRE( they.base_bmr() == 439 );
             CHECK( they.get_cardiofit() == 1088 );
             CHECK( they.get_stamina_max() == 6764 );
+            THEN( "they can run for 45 turns" ) {
+                CHECK( running_turns( they ) == 45 );
+            }
         }
 
         // Little (SMALL)
-        GIVEN( "tiny body size" ) {
+        GIVEN( "Little (SMALL) body size" ) {
             set_single_trait( they, "SMALL" );
             REQUIRE( they.get_size() == creature_size::small );
             REQUIRE( they.base_bmr() == 1014 );
             CHECK( they.get_cardiofit() == 1376 );
             CHECK( they.get_stamina_max() == 7628 );
+            THEN( "they can run for 51 turns" ) {
+                CHECK( running_turns( they ) == 51 );
+            }
         }
 
         // No size mutations - default avatar with medium body size
-        GIVEN( "medium body size" ) {
+        GIVEN( "Normal medium body size" ) {
             clear_avatar();
             REQUIRE( they.get_size() == creature_size::medium );
             REQUIRE( they.base_bmr() == base_bmr );
             CHECK( they.get_cardiofit() == base_bmr );
             CHECK( they.get_stamina_max() == base_stamina );
+            THEN( "they can run for 58 turns" ) {
+                CHECK( running_turns( they ) == 58 );
+            }
         }
 
-        // Large (LARGE)
-        GIVEN( "large body size" ) {
+        // Inconveniently Large (LARGE)
+        GIVEN( "Inconveniently Large (LARGE) body size" ) {
             set_single_trait( they, "LARGE" );
             REQUIRE( they.get_size() == creature_size::large );
             REQUIRE( they.base_bmr() == 2586 );
             CHECK( they.get_cardiofit() == 2162 );
             CHECK( they.get_stamina_max() == 9986 );
+            THEN( "they can run for 66 turns" ) {
+                CHECK( running_turns( they ) == 66 );
+            }
         }
 
         // Freakishly Huge (HUGE)
-        GIVEN( "huge body size" ) {
+        GIVEN( "Freakishly Huge (HUGE) body size" ) {
             set_single_trait( they, "HUGE" );
             REQUIRE( they.get_size() == creature_size::huge );
             REQUIRE( they.base_bmr() == 3589 );
             CHECK( they.get_cardiofit() == 2663 );
             CHECK( they.get_stamina_max() == 11489 );
+            THEN( "they can run for 76 turns" ) {
+                CHECK( running_turns( they ) == 76 );
+            }
+        }
+    }
+
+    SECTION( "minmaxing mutations" ) {
+        GIVEN( "Tiny and Hyperactive" ) {
+            they.clear_mutations();
+            they.toggle_trait( trait_id( "SMALL2" ) );
+            they.toggle_trait( trait_id( "GOODCARDIO2" ) );
+            THEN( "they can run for 76 turns" ) {
+                CHECK( running_turns( they ) == 54 );
+            }
+        }
+        GIVEN( "Freakishly Huge and Hyperactive" ) {
+            they.clear_mutations();
+            they.toggle_trait( trait_id( "HUGE" ) );
+            they.toggle_trait( trait_id( "GOODCARDIO2" ) );
+            THEN( "they can run for 76 turns" ) {
+                CHECK( running_turns( they ) == 97 );
+            }
         }
     }
 }