Skeletal muscle and cerebral oxygenation levels during and after submaximal concentric and eccentric isokinetic exercise.

The aim was to investigate the potential differences in muscle (vastus lateralis) and cerebral (prefrontal cortex) oxygenation levels as well as in the number of repetitions and total work output between isokinetic eccentric and concentric exercise at a moderate relative intensity until exhaustion. Ten recreationally active young men underwent two isokinetic exercise sessions either concentric or eccentric, one on each randomly selected leg. The protocols were performed at 60°/s and an intensity corresponding to 60% of the maximal voluntary contraction (MVC) of each contraction type. Concentric torque was significantly lower compared to eccentric torque in both peak values and at values corresponding to 60% of MVC [230 ± 18 Nm vs. 276 ± 19 Nm (P = .014) and 137 ± 12 Nm vs. 168 ± 11 Nm, respectively (P = .010)]. The participants performed 40% more contractions during eccentric compared to concentric exercise [122 ± 15 vs. 78 ± 7, respectively]. No differences were found in the levels of oxyhaemoglobin, deoxyhemoglobin, total haemoglobin and tissue saturation index when eccentric and eccentric exercise regimes were compared (all P > .05). Our results demonstrate that eccentric exercise of moderate intensity leads to greater resistance to fatigue and more work output compared to concentric exercise, despite the comparable muscle and cerebral oxygenation levels.

Dietary Cysteine Intake is Associated with Blood Glutathione Levels and Isometric Strength.

Glutathione is the most abundant cellular antioxidant and regulates redox homeostasis. Healthy individuals with certain antioxidant inadequacies/deficiencies exhibit impairments in physiological functions. The aim was to investigate whether low levels of dietary cysteine intake are associated with a) lower erythrocyte glutathione, b) increased plasma F2-isoprostanes, and c) impaired muscle function. Towards this aim, we recorded the dietary intake of the three amino acids that synthesize glutathione (i. e., glutamic acid, cysteine, and glycine) in forty-one healthy individuals, and subsequently measured erythrocyte glutathione levels. Maximal isometric strength and fatigue index were also assessed using an electronic handgrip dynamometer. Our findings indicate that dietary cysteine intake was positively correlated with glutathione levels (r=0.765, p<0.001). In addition, glutathione levels were negatively correlated with F2-isoprostanes (r=- 0.311, p=0.048). An interesting finding was that glutathione levels and cysteine intake were positively correlated with maximal handgrip strength (r=0.416, p=0.007 and r=0.343, p=0.028, respectively). In conclusion, glutathione concentration is associated with cysteine intake, while adequate cysteine levels were important for optimal redox status and muscle function. This highlights the importance of proper nutritional intake and biochemical screening with the goal of personalized nutrition.

Young tennis players and balance performance.

The purpose of the present study was to investigate the effect of a tennis training session on the balance performance of young tennis players. The study was conducted on 36 elite tennis players (age 14 +/- 2 years; body mass 55 +/- 6 kg; body height 165 +/- 6 cm; mean +/- SD) participating in the national young tennis championship. Balance performance was assessed before and immediately after a tennis training session (pre-training and post-training, respectively). The balance assessment was performed with 2 different balance boards and the Biodex Stability System. In addition, dynamometric measurements of peak isokinetic moment in the knee flexors and extensors were performed pre and post tennis training session, to quantify the degree of muscle fatigue induced by the tennis training session. One-way analysis of variance with repeated measures was used to test for differences in balance performance and in isokinetic performance between pre and post tennis training session. The data analysis revealed no significant differences (p > 0.05) in balance performance, whereas there were significant differences in knee joint moment production between pre and post tennis training measures. Although the tennis training session of the present study had no significant effect (p > 0.05) on any of the balance performance indicators examined, there was a decline in balance performance, which suggests that different level of fatigue for an extended period (games) will have greater effect on balance performance. It is suggested that a tennis-specific balance exercise program should be included in the tennis training session.