Relationships between rating of perceived exertion, heart rate and blood lactate during continuous and alternated-intensity cycling exercises

This study aimed to: i) use Borg's scale of rating perceived exertion (RPE) in the prescription of cycling training exercises with alternated intensity (S); ii) determine the relationships between RPE and the indices of physiological strains, e.g. heart rate (HR) and blood lactate ([La]), measured during S compared to continuous exercises (C). HR, [La] and RPE were measured in 11 active men at the 5th and 10th minutes of cycling exercises. These exercises were performed with constant or varying intensity corresponding to average power outputs (APO) equal to 160 and 240 W. The protocols with varying intensity consisted of alternated short periods (10 s: S10, or 20 s: S20) of medium and high intensity (120-200 W for APO-160 W and 200-280 W for APO-240 W). During S exercises HR, [La] and RPE were significantly higher compared to C exercises. This effect was more pronounced when the duration of alternated-intensity bouts was longer (S20 versus S10 protocols). The relationships between HR, [La] and RPE (mean or individual data) were not significantly different for the different protocols. However, there was a shift in the relationship between RPE and HR measured at the 5th and 10th minutes of exercise (p<0.001). Moreover, in each protocol, there were significant differences in the individual values of HR or [La] corresponding to the same RPE. The relationships between HR, [La] and RPE were not different between C and S exercises. Individually determined RPE can be used in the prescription of training for both exercises.

Diurnal Rhythm of Muscular Strength Depends on Temporal Specificity of Self-Resistance Training

The study investigated the effect of the time-of-day at which maximal isometric voluntary co-contraction (MIVCC) training is conducted on the adaptation and diurnal variation of maximal and explosive force production. Twenty active men underwent a 6-week (3 times per week) MIVCC training of the right elbow joint. The participants were randomly assigned to a morning training group (MTG, 07:00-08:00 hours) and evening training group (ETG, 17:00-18:00 hours). The maximal voluntary force (MVF) and maximal rate of force development (MRFD) during isometric elbow flexion (MVFF and MRFD(F)) and extension (MVF(E) and MRFD(E)) were recorded before (T0) and after (T1) training in the morning and evening. At T0, MVF and MRFD were higher in the evening compared with those in the morning for the MTG and ETG (p ≤ 0.05). At T1, MVFF and MVFE increased in the morning and evening for both groups (p < 0.001). The MRFD(F) and MRFD(E) increased only if training and test session were scheduled at the same time. The relative increase of MVF was greater at the specific time of training for the MTG (12 and 17.6% in MVF(F) and MVF(E), respectively) and ETG (9.8 and 13.4% in MVF(F) and MVF(E), respectively). The diurnal variations in MVF and MRF(D) during flexion and extension disappeared in the MTG and persisted in the ETG. Maximal isometric voluntary co-contraction training enhanced muscle strength whatever the time-of-day at which the training was scheduled without alteration of explosive force. In contrast, to optimize the muscle strength, our results suggested that morning training may be accompanied by the greatest muscle strength gain and blunted muscle strength variation observed between the morning and evening.

Co-contraction training, muscle explosive force and associated electromyography activity

BACKGROUND

The effects of a six-week Maximal isometric voluntary co-contraction (MIVCC) training program of the elbow flexor and extensor muscles on maximal and explosive muscle strength have been studied.

METHODS

Ten active men underwent 6-week MIVCC. Maximal rate of force development (MRFD) of the elbow flexor (MRFDflex) and extensor (MRFDext) were measured in addition to maximal voluntary contraction (MVC) of these muscles (MVCflex and MVCext) before (T0), after 4-week (T1) and 6-week (T2) MIVCC training program. During each test session, integrated electromyographic activity (iEMG) of agonistic and antagonistic muscles during MVC, MRFD, submaximal contractions (30% and 60% MVC) and MIVCC of the elbow flexor and extensor muscles were measured.

RESULTS

At T2, MVCflex (13.3±11.7%) and MVCext (22.5±6.1%) increased significantly (P<0.001). Similarly, iEMG of agonists muscles during MVC increased significantly for flexor (+29.9%) and extensor (+29.6%) muscles (P<0.001) without changes of antagonists co-activation. The increases in MRFDflex (+12.5%), MRFDext (+9.2%) and iEMG at MRFD were not significant.

CONCLUSIONS

MIVCC training can simultaneously improve strength of antagonistic muscles without inducing an alteration of MRFD or an increase in muscles co-activation during contractions of the agonist muscles. Interestingly, the improvement of estimated forces during MIVCC after 6-week-training suggested that the higher level of MIVCC previously observed in bodybuilders could be the result of specific training exercises (posing). The fact that MIVCC training did not alter "explosive" force production, which is important in optimal design of sports-specific resistance training as well as in rehabilitation programs.

Modeling of Running Performances in Humans: Comparison of Power Laws and Critical Speed

Zinoubi, B, Vandewalle, H, and Driss, T. Modeling of running performances in humans: comparison of power laws and critical speed. J Strength Cond Res 31(7): 1859-1867, 2017-The concepts of power law and critical speed (SCrit) have been applied to the analysis of individual running performances. We have analyzed the results of 2 exceptional runners (Nurmi and Gebrselassie) and 11 physical education students (PESs) who performed 3 exhausting running exercises. Power laws can accurately describe the relationships between exhaustion time (tlim) and distance (Dlim) or speed (S) (Equation is included in full-text article.)in elite runners and PES. However, the validity of the application of power laws must be verified for higher values of tlim in nonelite runners. Exponent γ is close to 1 in elite runners and lower in PESs (from 0.625 to 0.872). The value of SCrit was computed from 2 values of tlim (3-14 minutes; SCrit 3-14) and was expressed as a fraction of maximal aerobic speed (MAS) which was assumed to correspond to the maximal speed that can be sustained over 7 minutes (Equation is included in full-text article.)The individual values of (Equation is included in full-text article.)(0.945 for Gebrselassie, 0.919 for Nurmi, and 0.764 ± 0.078 in PESs) were linearly correlated with γ (r > 0.999) and almost equal to γ (0.952 for Gebrselassie, 0.918 for Nurmi, and 0.779 ± 0.076 for PESs). The same results were observed when SCrit was computed for tlim equal to 6-28 minutes (SCrit 6-28) and MAS was the maximal velocity sustainable during 14 minutes (S14min). The fact that γ is linearly correlated and almost equal to (Equation is included in full-text article.)or (Equation is included in full-text article.)suggests that exponent γ can be considered as an index of aerobic endurance.