Neuromuscular Fatigue Responses Research Articles

The Dynamics of Locomotor Neuromuscular Fatigue during Ramp-Incremental Cycling to Intolerance.

Traditional neuromuscular fatigue assessments are not task-specific and are unable to characterize neuromuscular performance decline during dynamic whole-body exercise. This study used interleaved maximal isokinetic cycling efforts to characterize the dynamics of the decline in neuromuscular performance during ramp-incremental (RI) cycle ergometry exercise to intolerance. Eleven young healthy participants (10 male/1 female) performed two RI cycle ergometry exercise tests to intolerance: [1] RI-exercise with peak isokinetic power (Piso) at 80 rev·min-1 measured at baseline and immediately at intolerance from a maximal ~6 s effort; [2] RI-exercise where additional Piso measurements were interleaved every 90 s to characterize the decline in neuromuscular performance during the RI-test. Muscle excitation was measured using EMG during all Piso assessments, and pulmonary gas exchange was measured throughout. Baseline Piso was 832 ± 140 W and RI-exercise reduced Piso to 349 ± 96 W at intolerance (p = 0.001), which was not different from flywheel power at intolerance (303 ± 96 W; p = 0.292). There was no reduction in Piso between baseline cycling and gas exchange threshold (GET; baseline Piso vs. mean Piso below GET: 828 ± 146 vs. 815 ± 149 W; p = 1.00). Piso fell progressively above GET until intolerance (Piso every 90 s above GET: 759 ± 139; 684 ± 141; 535 ± 144; 374 ± 117 W; each p < 0.05 vs. baseline and mean Piso below GET). Peak muscle excitation (EMG) was also reduced only above GET (73 ± 14 % of baseline, at intolerance; p < 0.05). However, the reduction in peak Piso preceded the reduction in peak muscle excitation. The dynamics of the decline in neuromuscular performance (reduction in Piso and EMG) during RI-exercise are consistent with known intensity-dependent metabolic and traditional pre-post neuromuscular fatigue responses to discrete bouts of constant-power exercise.

Neuromuscular Fatigue Responses of Endurance- and Strength-Trained Athletes during Incremental Cycling Exercise.

This study explored the development of neuromuscular fatigue responses during progressive cycling exercise. The sample comprised 32 participants aged 22.0 ± 0.54 years who were assigned into three groups: endurance-trained group (END, triathletes, n = 10), strength-trained group (STR, bodybuilders, n = 10) and control group (CG, recreationally active students, n = 12). The incremental cycling exercise was performed using a progressive protocol starting with a 3 min resting measurement and then 50 W workload with subsequent constant increments of 50 W every 3 min until 200 W. Surface electromyography (SEMG) of rectus femoris muscles was recorded during the final 30 s of each of the four workloads. During the final 15 s of each workload, participants rated their overall perception of effort using the 20-point rating of the perceived exertion (RPE) scale. Post hoc Tukey’s HSD testing showed significant differences between the END and STR groups in median frequency and mean power frequency across all workloads (p < 0.001 and p < 0.01, respectively). Athletes from the END group had significantly lower electromyogram amplitude responses than those from the STR (p = 0.0093) and CG groups (p = 0.0006). Increasing RPE points from 50 to 200 W were significantly higher in the STR than in the END group (p < 0.001). In conclusion, there is a significant variation in the neuromuscular fatigue profiles between athletes with different training backgrounds when a cycling exercise is applied. The approximately linear trends of the SEMG and RPE values of both groups of athletes with increasing workload support the increased skeletal muscle recruitment with perceived exertion or fatiguing effect.

Neuromuscular Fatigue Following Cycling To Task Failure In Different Exercise Intensity Domains

Neuromuscular (NM) fatigue can vary according to exercise intensity and duration; however, fatigue responses across the full spectrum of exercise intensities to task failure remain unclear. PURPOSE: To characterize the central and peripheral NM fatigue responses to cycling to task failure in different exercise intensity domains. METHODS: After a ramp incremental test, 12 healthy, active males (29 ± 5 years) underwent 4 cycling sessions to task failure at 5% below gas exchange threshold (moderate domain; MOD), 5% below the maximal metabolic steady state; HVY), 5% below peak power output (severe domain; SVR), and 120% of peak power output (extreme domain; EXT). At baseline, upon task failure (post), and following 1, 4, and 8 min of recovery, participants performed an NM assessment consisting of a maximal voluntary isometric contraction (MVC) with superimposed and potentiated high frequency doublets (Db100), followed by a low frequency doublet (Db10) and single twitch (QTw). Two-way repeated measures ANOVAs with Bonferroni post hoc examined 4 domains 5 timepoints. RESULTS: MVC declined to the same extent in all domains at post (all p > 0.05) and although not fully recovered at 8 min, the fastest recovery from post was displayed after EXT (+59.5 ± 79.0%) compared to MOD (+9.4 ± 32.0%, p = 0.035), HVY (+17.7 ± 21.8%, p = 0.021), and SVR (+29.8% ± 29.9%, p = 0.016). Voluntary activation at post was lowest after MOD (-11.1 ± 11.6%) compared to EXT (-0.5 ± 4.6%, p = 0.030), and all conditions fully recovered to baseline without differences between domains at 8 min (all p > 0.05). While QTwat post displayed greatest decline in EXT (-50.5 ± 14.7%) and least in MOD (-7.5 ± 28.3%, p = 0.011), EXT (+86.1 ± 69.2%) partially recovered by 8 min to match MOD values (+2.3 ± 17.7%, p = 0.865). Low frequency fatigue (Db10:100) at post was lowest in MOD (-8.6 ± 6.1%) compared to HVY (-18.4 ± 7.9%, p = 0.007), SVR (-22.8 ± 9.3%, p = 0.020), and EXT (-24.8 ± 10.7%, p < 0.001), but all conditions partially recovered from post to match MOD values at 8 min (+2.3 ± 7.2%, all p > 0.05). CONCLUSIONS: Although MVC declined to the same extent following exercise to task failure in all domains, our data confirm that the contribution of central and peripheral factors to this decline differed between conditions. Different NM fatigue recovery patterns were also demonstrated during recovery.

Distinct pacing profiles result in similar perceptual responses and neuromuscular fatigue development: Why different “roads” finish at the same line?

ABSTRACT The current study analysed the effect of distinct pacing profiles (i.e. U, J, and inverted J) in the perceptual responses and neuromuscular fatigue (NMF) development following a 4-km cycling time trial (TT). Twenty-one cyclists with similar training status were allocated into three different groups based on their pacing profile spontaneously adopted during TT. Rating of perceived exertion (RPE), oxygen uptake (⩒O2) and heart rate (HR) were continuously recorded. NMF was assessed by using isometric maximal voluntary contractions (IMVC), while the central [i.e. voluntary activation (VA)] and peripheral fatigue of knee extensors [i.e. peak torque of potentiated twitches (TwPt)] were evaluated using electrically evoked contractions performed pre and 2 min after the TT. TT performance was not different amongst pacing profiles (U = 377 ± 20 s; J = 392 ± 23 s; J-i = 381 ± 20 s) (all P > 0.05). RPE, ⩒O2 and HR increased similarly throughout the TT regardless the pacing strategy (all P > 0.05). Similarly, IMVC (U = −9.9 ± 8.8; J = −9.6 ± 4.5%; J-i = −13.8 ± 11.3%), VA (U = −2.3 ± 1.7%; J = −5.4 ± 2.2%; J-i = −6.4 ± 4.5%) and TwPt (U = −32.5 ± 12.0%; J = −29.5 ± 8.0%; J-i = −33.6 ± 13.6%) were similar amongst pacing profiles (all P > 0.05). Therefore, endurance athletes with similar training status showed the same perceived responses and NMF development regardless the pacing profile spontaneously adopted. It was suggested that these responses occurred in order to preserve a similar rate of change in systemic responses (i.e. RPE, ⩒O2 and HR) and NMF development, ultimately resulting in same TT performance. Highlights Different pacing profiles resulted in the same performance in a 4-km cycling time trial. The similar performance might be due to achievement of the same sensory tolerance limit. There was no difference for perceptual, metabolic and neuromuscular fatigue responses.

Longer Concentric Action Increases Muscle Activation and Neuromuscular Fatigue Responses in Protocols Equalized by Repetition Duration.

Lacerda, LT, Costa, CG, Lima, FV, Martins-Costa, HC, Diniz, RCR, Andrade, AGP, Peixoto, GHC, Bemben, MG, and Chagas, MH. Longer concentric action increases muscle activation and neuromuscular fatigue responses in protocols equalized by repetition duration. J Strength Cond Res 33(6): 1629-1639, 2019-The aim of this study was to investigate the impact of protocols equalized by the repetition duration but composed of different concentric (CON) and eccentric (ECC) durations on muscle activation and neuromuscular fatigue. Seventeen males with previous experience in resistance training performed 3 training protocols (A - 2 second CON: 4 second ECC; B - 3 second CON: 3 second ECC; and C - 4 second CON: 2 second ECC) with the Smith machine bench press exercise, all with 3 sets, 6 repetitions, 3 minutes' rest, and 60% of 1RM. The normalized root mean square of the electromyographic signal (EMGRMS) and mean frequency electromyography (EMGMF) for pectoralis major and triceps brachii muscles were calculated for second and fifth repetitions in each set. The results showed an EMGMF decrease across the repetitions accompanied by a progressive increase of the EMGRMS across the repetitions for all protocols and muscles. The EMGRMS was higher in protocol C when compared with protocol A and B for pectoralis major. The EMGMF was lower in protocols B and C than in protocol A for pectoralis major throughout the sets and repetitions. A higher EMGRMS and a lower EMGMF were observed in protocols B and C compared with protocol A for triceps brachii, solely in the fifth repetition. In conclusion, training protocols conducted with the same repetition duration, but with different concentric and eccentric durations, produce distinct muscle activation and neuromuscular fatigue responses, in which performing longer concentric durations could be the more appropriate strategy to increase muscle activation and neuromuscular fatigue.