SMITH, D. J., and S. R. NORRIS. Changes in glutamine and glutamate concentrations for tracking training tolerance. Med. Sci. Sports Exerc., Vol. 32, No. 3, pp. 684–689, 2000.
Purpose: The purpose was to monitor high-performance athletes throughout training macrocycles and competitions and examine the changes in plasma glutamine (Gm) and glutamate (Ga) concentrations in order to develop a model of tolerance to training.
Methods: Plasma glutamine and glutamate concentrations of 52 National team athletes (31 male and 21 female) divided into male and female groups of speed skating, swimming, and cross-country skiing were measured in an early season rested condition to determine highest Gm and lowest Ga concentrations and over 2–4 macrocycles, which included heavy training to establish lowest Gm and highest Ga concentrations.
Results: In the rested condition, there were no differences within and between the male and female groups, excluding five athletes (OTA) who became overtrained in heavy training. The mean (±SD) Gm concentration was 585 ± 54 μmol·L−1, Ga concentration 101 ± 16 μmol·L−1, and Gm/Ga ratio 5.88 ± 0.84 μmol·L−1. The OTA had a significantly higher Ga concentration of 128 ± 16 μmol·L−1 and lower Gm/Ga ratio of 4.43 ± 0.49 μmol·L−1 than all the other groups. In heavy training, there was a significant decrease (P < 0.05) in Gm concentration to 522 ± 53 μmol·L−1, significant increase in Ga concentration to 128 ± 19 μmol·L−1 and significant decrease in Gm/Ga ratio to 4.15 ± 0.57 μmol·L−1. The OTA Gm concentration of 488 ± 31 μmol·L−1 was significant lower than only the male speed skating and swimming groups. However, the Ga concentration of 171 ± 17 μmol·L−1 and Gm/Ga ratio of 2.88 ± 0.27 μmol·L−1 were significantly higher and lower respectively than all other groups.
Conclusions: Based on the changes in Gm and Ga concentration under different training conditions, we propose an athlete tolerance to training model where glutamine concentration reflects tolerance to volume of work and glutamate concentration reflects tolerance to high intensity training. We suggest that the Gm/Ga ratio may globally represent overall tolerance to training.
Overtraining is a common problem in high-performance sport and has unfortunately been used as a “catch-all” phrase to describe athletes who exhibit performance incompetence, prolonged fatigue, or an inability to train at expected levels. Athletes constantly seek to push the window of positive training adaptation to find an edge in performance but in so doing run the risk of functional impairment, which has been described by some researchers as staleness or burnout (13,17). In reality, it is likely that an athlete is in a constant flux along a continuum of positive and negative responses primarily dictated by the balance or imbalance of training intensity, volume, and recovery time between workouts. It has been suggested that along this continuum ranging from peak performance to performance incompetence, short-term overtraining or overreaching exists during which performance recovery is possible within up to 2 wk after intensive training (4,9,15,19). However, if recovery is inadequate or the training load is unmanageable, overreaching can progress to overtraining where recovery may take weeks or months (14,19,22). The interindividual variability in recovery potential, exercise capacity, nontraining stress factors, and stress tolerance may explain the different vulnerability of athletes to training under identical training stress conditions (22). Furthermore, this individual tolerance may explain why attempts to experimentally produce overtraining have not been successful.
Although many indicators of overreaching (34) and overtraining (10) have been proposed, the diagnosis of overtraining broadly defined as an imbalance between training and recovery (21) has been scientifically difficult because overtraining may result from a multitude of factors, including anabolic/catabolic imbalance (1), hormonal dysfunction of the hypothalamic-pituitary axis (4), amino acid imbalance (3,29), and autonomic dysfunction (14) together with nontraining stressors (22). Overtraining interpretation is frequently based on professional experience and individual case studies (22,36) and although overtraining studies have been attempted, the interindividual variability of the of the multitude of factors involved in the mosaic of overtraining has hampered the identification of definitive signals of this process.
Although extensive blood profiles of athletes have been reported in prospective relatively short-term overreaching/overtraining studies (20,22) and in retrospective situations when overtraining has been diagnosed (17,32), it has been suggested that the single measure of an elevated plasma glutamine concentration in an athlete represents a positive adaption to a well-balanced training program, whereas a lower concentration observed in an overtrained athlete could be a negative effect of exercise stress (32). In addition, prolonged periods of fatigue, exacerbated by exercise have also been associated with recurrent infections (8). Glutamine is the most abundant amino acid in the body (18) where skeletal muscle provides the majority of plasma glutamine required by the gastrointestinal tract (26,35), cells of the immune system (2,28,30), and the kidney during acidosis (7,38). Furthermore, glutamine may be important in the regulation of protein synthesis and degradation (25).
The possible link between overtraining and glutamine currently stems from two studies. Lower plasma glutamine concentrations were observed in athletes suffering from overtraining than age-matched controls (30), and Rowbottom et al. (32) reported that only glutamine deviated significantly from the normal range among a battery of standard blood parameters in overtrained athletes. In addition to lower plasma glutamine concentration in overtrained athletes, Parry-Billings et al. (30) reported significantly higher plasma glutamate concentration compared with controls. Although it remains to be shown that there is any correlation between glutamine concentration and physical capability, the data suggest a link may exist and warrants further investigation (32).
Thus, the purpose of this study was to monitor high performance athletes throughout training macrocycles and competitions and examine the changes in plasma glutamine and glutamate concentrations in an attempt to develop a model of tolerance to training.