The purpose of this study was to examine the concentration of blood ammonia (NH
$_3$
) and lactate (La
$^-$
) responses to separate isokinetic arm exercise (AE) and leg exercise (LE). Eleven healthy non-trained subjects (aged 18--22∼yrs, 5 males, 6 females) completed 50 maximal effort concentric isokinetic contractions at 60°/sec for preferred arm (elbow joint) and leg (knee joint) on two separate occasions. Blood was drawn before exercise (Rest), immediately following exercise (End-Ex) and 10 minutes post-exercise (Post-10) and analysed for NH
$_3$
and La
$^-$
. The exercise intensity was assessed after exercise by presenting the mean(± SE) torque output as a percentage of the peak torque output following the 50 contractions for both AE and LE. The exercise intensity was 78.3 ± 1.4% AE respectively. The fatigue index is a ratio of beginning torque to end torque within the exercise period, which was 62.7 ± 3.7% 78.5 ± 2.8% statistically analysed by ANOVA with repeated measures. There was an increase in NH
$_3$
following AE between Rest and End-Ex from 92.7± 7.6 μmol.l
$^{-1}$
to 115.3 ± 11.4 μmol.l
$^{-1}$
, p < 0.05. There was an increase in La
$^-$
following AE between Rest to End-Ex from 1.6 ± 0.10 mmol.l
$^{-1}$
to 2.8 ± 0.24 mmol.l
$^{-1}$
, p < 0.05. The La
$^-$
increased for LE between End-Ex and Post-10 from 2.4± 0.23 to 3.3±0.41 mmol.l
$^{-1}$
, p < 0.05. These data suggest a more severe metabolic stress during fatiguing concentric isokinetic AE compared with LE and are consistent with previous findings.
