Acute responses of strength-related gene expressions to maximum strength and force sense acuity.

Background/aim: Although high muscle strength worsens the sense of force, it is unknown whether there is a relationship between this deterioration and the underlying molecular mechanisms. This study examined the relationship between decreased force sense (FS) acuity and strength-related gene expressions. Materials and methods: Maximal voluntary isometric contraction (MVIC) and FS (50% MVIC) tests were performed on the knee joints of twenty-two subjects. The expression analyses were evaluated by qRT-PCR in blood samples taken before, after MVIC, after 50% MVIC, and 15 min after the test. Results: MVIC and FS error values were significantly correlated with each other (r = .659, p = .001). The qRT-PCR analyses demonstrated that the expressed mRNAs of the interleukin 6 (IL-6), alpha-actinin 3 (ACTN3), angiotensin-converting enzyme (ACE), brain-derived neurotrophic factor (BDNF), and ciliary neurotrophic factor receptor (CNTFR) genes dramatically increased until 50% MVIC and subsequently decreased 15 min after the exercise (p < .05). The muscle-specific creatine kinase (CKMM), myosin light chain kinase (MLCK), and G-protein ß3 subunit (GNB3) genes reached their peak expression levels 30 min after MVIC (p < .05). ACE and ACTN3 gene expression increased significantly in parallel with the increased FS error (p < .05). These gene expression fluctuations observed at 50% MVIC and after the rest could be related to changes in cellular metabolism leading to fatigue. Conclusion: The time points of gene expression levels during exercise need to be considered. The force acuity of those whose maximal force develops too much may deteriorate.

Effect of Force Sense to Active Joint Position Sense and Relationships between Active Joint Position Sense, Force Sense, Jumping and Muscle Strength.

We aimed to investigate the effect of external load on the joint position sense (JPS) accuracy and its relation to the target jump height. The present study also aimed to explore the relationship between force sense (FS) and maximum voluntary isometric contraction (MVIC). Participants' MVIC levels were determined during the 45-degree knee extension task. Then, participants were asked to execute a knee JPS task with external load (EL-JPS) and with no-load (EL-JPS). To assess jumping accuracy participants were instructed to jump with their 50% of maximum jump height. Results indicated that EL-JPS error values were lower than NL-JPS. EL-JPS was correlated to jumping errors. However, the relationship between NL-JPS and jumping errors was not significant. A significant correlation was found between MVIC and FS errors.

Effects of 2 Different External Loads on Joint Position Sense and the Relationship Between Muscle Strength and Force Sense.

CONTEXT: Joint position sense (JPS) tests of proprioception lack ecological validity because the testing conditions are so different from the normal function that they can contribute little to understanding the role proprioception plays in daily and sporting activities. OBJECTIVE: To evaluate the effect of low and high external load on the knee JPS and to investigate the relationship between maximum voluntary isometric contraction and force sense (FS). DESIGN: Experimental study. SETTING: Research laboratory. PARTICIPANTS: A total of 47 volunteers with no history of knee pathology. INTERVENTIONS: Three active JPS tests performed with no load, low load, and high load were compared at the 45° target angle. For isometric FS test, 50% load was used. For isotonic low load and high load JPS tests, 30% and 70% loads were applied, respectively. MAIN OUTCOME MEASURES: To analyze obtained data set 2-way multiple analysis of variance, repeated measures of analysis of variance, paired sample t test, and the Pearson correlation coefficient were used. RESULTS: JPS was not affected by gender (male and female) and activity levels (sedentary, recreational, and trained). Results of the repeated measure of analysis of variance demonstrated the significant main effect of loads (P = .001). Significant differences were found between no load, low load, and high load JPS (P = .001). A positive and significant correlation was found between maximum voluntary isometric contraction and FS error values (r = .41, P = .001). CONCLUSIONS: The results suggest that as the load level increases, the knee JPS improves. Knee JPS assessed under external load may be a more appropriate alternative to the nature of the sport. Those with higher muscle strength have a worse FS.