143 Research paper Ammonia and lactate responses to isokinetic arm and leg exercise P.S. Micalos ∗ , F.E. Marino, K. Tarpenning, D. Kay and M. Gard Human Movement Studies Unit, Charles Sturt University, Bathurst, NSW 2795, Australia The purpose of this study was to examine the concentra- tion of blood ammonia (NH3) 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 ex- ercise (End-Ex) and 10 minutes post-exercise (Post-10) and analysed for NH3 and La − . The exercise intensity was as- sessed 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 in- tensity was 78.3 ± 1.4% and 78.7 ± 1.5% for LE and AE respectively. The fatigue index is a ratio of beginning torque to end torque within the exercise period, which was 62.7 ± 3.7% and 78.5 ± 2.8% for LE and AE, respectively. The biochemical data were statistically analysed by ANOVA with repeated measures. There was an increase in NH3 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 sug- gest a more severe metabolic stress during fatiguing concen- tric isokinetic AE compared with LE and are consistent with previous findings. ∗ Address for correspondence: Peter Micalos, Human Movement Studies Unit, Charles Sturt University, Bathurst, NSW 2795, Aus- tralia. Tel./Fax: +61 2 63384505; E-mail: pmicalos@csu.edu.au. 1. Introduction During intense short-duration exercise, skeletal mus- cle produces ammonia (NH 3 ) from the purine nu- cleotide cycle [4]. The production of NH 3 within mus- cle is increased when the adenine nucleotide pool is deaminated to form inosine monophosphate and NH 3 by the enzyme AMP deaminase [27,31]. Ammonia has been demonstrated to interfere directly with the mechanical function of skeletal muscle [29] and has been linked to the development of fatigue [17,23,27]. It has also been suggested that the increase in blood NH 3 following intense physical exercise may provide a metabolic marker for the degree of exercise stress [4]. The concentration of blood NH 3 has been shown to be dependent on the exercise protocol applied. Pro- longed submaximal exercise has shown blood NH 3 concentration to steadily increase over the exercise pe- riod [7,20]. During low intensity exercise NH 3 re- mains similar to resting values with a distinct upward inflection in the course of increasing exercise inten- sity [1]. During high intensity exercise, the concen- tration of NH 3 has been shown to increase in propor- tion to the workload [3,8,33]. However, NH 3 has been shown to respond differently to various exercise modes at similar exercise intensity. Previous research [6,34] has demonstrated a higher NH 3 response to bicycle ex- ercise compared with treadmill exercise at equivalent exercise intensity. Similarly, the NH 3 response to arm exercise (AE) has been shown to be higher compared with leg exercise (LE) at the same aerobic exercise in- tensity [18], indicating a higher metabolic stress with AE. Blood NH 3 levels have been measured simultane- ously with blood lactate (La − ) to define the relation- ship between these two metabolites during exercise. Research has revealed a significant correlation between blood NH 3 and La − leading to the suggestion that the production of NH 3 is closely linked to exercise inten- Isokinetics and Exercise Science 9 (2001) 143–149 ISSN 0959-3020 / $8.00  2001, IOS Press. All rights reserved