Adaptive changes in motor control of rhythmic movement after maximal eccentric actions

Adenosine A2A receptor gene polymorphisms (ADORA2A) are associated with maximal concentric contraction pain

Objectives

To test associations of adenosine A2A receptor gene (ADORA2A) polymorphisms with maximal concentric contraction pain, caffeine-induced perceptual changes, and responses to mild eccentric injury.

Design

Targeted candidate gene association study.

Methods

ADORA2A (rs5751876) was genotyped in 26 adults. Pain of a maximal elbow flexor contraction was assessed. Participants performed 18 eccentric actions of the elbow flexors. Arm volume was measured before and 24- and 48-h post-injury. At 24- and 48-h post-injury, caffeine or placebo capsules were given using a randomized cross-over design and effort and pain were assessed.

Results

Maximal concentric contraction pain was higher for the CC compared to the CT/TT group (effect size d = 0.89) and lower for the TT compared to the CT/CC group (d = 0.62). There were moderate sized differences between CC and TT/CT groups for post-injury exertion and arm volume 24-h post injury.

Conclusions

ADORA2A polymorphisms are moderately associated with muscle pain during maximal contractions in uninjured muscle.

Foam rolling for delayed-onset muscle soreness and recovery of dynamic performance measures

CONTEXT

After an intense bout of exercise, foam rolling is thought to alleviate muscle fatigue and soreness (ie, delayed-onset muscle soreness [DOMS]) and improve muscular performance. Potentially, foam rolling may be an effective therapeutic modality to reduce DOMS while enhancing the recovery of muscular performance.

OBJECTIVE

To examine the effects of foam rolling as a recovery tool after an intense exercise protocol through assessment of pressure-pain threshold, sprint time, change-of-direction speed, power, and dynamic strength-endurance.

DESIGN

Controlled laboratory study.

SETTING

University laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 8 healthy, physically active males (age = 22.1 ± 2.5 years, height = 177.0 ± 7.5 cm, mass = 88.4 ± 11.4 kg) participated.

INTERVENTION(S)

Participants performed 2 conditions, separated by 4 weeks, involving 10 sets of 10 repetitions of back squats at 60% of their 1-repetition maximum, followed by either no foam rolling or 20 minutes of foam rolling immediately, 24, and 48 hours postexercise.

MAIN OUTCOME MEASURE(S)

Pressure-pain threshold, sprint speed (30-m sprint time), power (broad-jump distance), change-of-direction speed (T-test), and dynamic strength-endurance.

RESULTS

Foam rolling substantially improved quadriceps muscle tenderness by a moderate to large amount in the days after fatigue (Cohen d range, 0.59 to 0.84). Substantial effects ranged from small to large in sprint time (Cohen d range, 0.68 to 0.77), power (Cohen d range, 0.48 to 0.87), and dynamic strength-endurance (Cohen d = 0.54).

CONCLUSIONS

Foam rolling effectively reduced DOMS and associated decrements in most dynamic performance measures.

Motor unit activity after eccentric exercise and muscle damage in humans

It is well known that unaccustomed eccentric exercise leads to muscle damage and soreness, which can produce long-lasting effects on muscle function. How this muscle damage influences muscle activation is poorly understood. The purpose of this brief review is to highlight the effect of eccentric exercise on the activation of muscle by the nervous system, by examining the change in motor unit activity obtained from surface electromyography (EMG) and intramuscular recordings. Previous research shows that eccentric exercise produces unusual changes in the EMG–force relation that influences motor performance during isometric, shortening and lengthening muscle contractions and during fatiguing tasks. When examining the effect of eccentric exercise at the single motor unit level, there are substantial changes in recruitment thresholds, discharge rates, motor unit conduction velocities and synchronization, which can last for up to 1 week after eccentric exercise. Examining the time course of these changes suggests that the increased submaximal EMG after eccentric exercise most likely occurs through a decrease in motor unit conduction velocity and an increase in motor unit activity related to antagonist muscle coactivation and low-frequency fatigue. Furthermore, there is a commonly held view that eccentric exercise produces preferential damage to high-threshold motor units, but the evidence for this in humans is limited. Further research is needed to establish whether there is preferential damage to high-threshold motor units after eccentric exercise in humans, preferably by linking changes in motor unit activity with estimates of motor unit size using selective intramuscular recording techniques.

Eccentric exercise and delayed onset muscle soreness of the quadriceps induce adjustments in agonist-antagonist activity, which are dependent on the motor task

This study investigates the effects of eccentric exercise and delayed onset muscle soreness (DOMS) of the quadriceps on agonist–antagonist activity during a range of motor tasks. Ten healthy volunteers (age, mean ± SD, 24.9 ± 3.2 years) performed maximum voluntary contractions (MVC) and explosive isometric contractions of the knee extensors followed by isometric contractions at 2.5, 5, 10, 15, 20, and 30% MVC at baseline, immediately after and 24 h after eccentric exercise of the quadriceps. During each task, force of the knee extensors and surface EMG of the vasti and hamstrings muscles were recorded concurrently. Rate of force development (RFD) was computed from the explosive isometric contraction, and the coefficient of variation of the force (CoV) signal was estimated from the submaximal contractions. Twenty-four hours after exercise, the subjects rated their perceived pain intensity as 4.1 ± 1.2 (score out of 10). The maximum RFD and MVC of the knee extensors was reduced immediately post- and 24 h after eccentric exercise compared to baseline (average across both time points: 19.1 ± 17.1% and 11.9 ± 9.8% lower, respectively, P < 0.05). The CoV for force during the submaximal contractions was greater immediately after eccentric exercise (up to 66% higher than baseline, P < 0.001) and remained higher 24 h post-exercise during the presence of DOMS (P < 0.01). For the explosive and MVC tasks, the EMG amplitude of the vasti muscles decreased immediately after exercise and was accompanied by increased antagonist EMG for the explosive contraction only. On the contrary, reduced force steadiness was accompanied by a general increase in EMG amplitude of the vasti muscles and was accompanied by increased antagonist activity, but only at higher force levels (>15% MVC). This study shows that eccentric exercise and subsequent DOMS of the quadriceps reduce the maximal force, rate of force development and force steadiness of the knee extensors, and is accompanied by different adjustments of agonist and antagonist muscle activities.

Changes in the spatio-temporal organization of the trapezius muscle activity in response to eccentric contractions

We hypothesized changes in the spatial organization of the trapezius muscle electromyographic (EMG) activity after a shoulder eccentric exercise. The rate of perceived exertion (RPE), the size of the soreness area, maximum force and, EMG from the upper, middle and lower trapezius were recorded. Root mean square (RMS), mean frequency (MNF) and normalized mutual information (a measure of functional connectivity between muscle sub-divisions) were computed during submaximal dynamic and static contractions performed before, immediately after and 24 h after exercise. Immediately after exercise, RPE, soreness area, RMS from the upper and middle trapezius and normalized mutual information among upper-middle sub-divisions increased while MNF decreased for the middle trapezius (P<0.05). After 24 h, the maximum force decreased. RMS from the upper trapezius and normalized mutual information among upper-middle trapezius sub-divisions were higher than before exercise. MNF values increased from immediately after to 24 h after for the upper and lower trapezius (P<0.05). The current results underlined changes in the spatio-temporal organization of the trapezius in response to shoulder eccentric exercise. The observed changes in EMG temporal and spectral contents and the enhanced sub-division coupling underlined the functional role of spatial variations of the EMG activity during muscle fatigue and in the presence of delayed-onset muscle soreness.

Interactive effects of acute experimental pain in trapezius and sored wrist extensor on the electromyography of the forearm muscles during computer work

We investigated the interactive effects of shoulder pain and wrist extensor muscle soreness on surface electromyography (EMG) during computer mouse work. On day one, subjects (N = 12) performed computer work with/without acute muscle pain induced in the trapezius muscle. Subsequently, eccentric exercise was performed to induce delayed onset muscle soreness (DOMS) in wrist extensor muscles. In presence of DOMS on day two, computer work recordings with/without pain were repeated. EMG signals were recorded from the descending part of trapezius bilaterally, flexor carpi ulnaris and extensor carpi radialis brevis. Experimental muscle pain in trapezius led to a decrease in the muscular activity of the wrist extensor (P < 0.02) and decreased the relative rest time in the wrist flexor even in presence of DOMS (P < 0.01). The present result suggests that shoulder pain plays a role in the coordination of wrist flexors and extensors during computer work.

Disturbed motor control of rhythmic movement at 2 h and delayed after maximal eccentric actions

The aim of this study was to examine the influence of exercise-induced muscle damage on elbow rhythmic movement (RM) performance and neural activity pattern and to investigate whether this influence is joint angle specific. Ten males performed an exercise of 50 maximal eccentric elbow flexions in isokinetic machine with duty cycle of 1:15. Maximal dynamic and isometric force tests (90 degrees , 110 degrees and 130 degrees elbow angle) and both active and passive stretch reflex tests of elbow flexors were applied to the elbow joint. The intentional RM was performed in the horizontal plane at elbow angles; 60-120 degrees (SA-RM), 80-140 degrees (MA-RM) and 100-160 degrees (LA-RM). All measurements together with the determination of muscle soreness, swelling, passive stiffness, serum creatine kinase were conducted before, immediately and 2h as well as 2 days, 4 days, 6 days and 8 days post-exercise. Repeated maximal eccentric actions modified the RM trajectory symmetry acutely (SA-RM) and delayed (SA/MA/LA-RM) until the entire follow up of 8 days. Acutely lowered MA-RM peak velocity together with reduced activity of biceps brachii (BB) at every RM range, reflected a poorer acceleration and deceleration capacity of elbow flexors. A large acute drop of BB EMG burst amplitude together with parallel decrease in BB active stretch reflex amplitude, especially 2h post-exercise, suggested an inhibitory effect originating most likely from groups III/IV mechano-nociceptors.

Effects of eccentric exercise on trapezius electromyography during computer work with active and passive pauses

BACKGROUND

The aim of this laboratory study was to investigate the effects of eccentric exercises on the trapezius muscle spatial electromyographic (EMG) activity during computer work with active and passive pauses.

METHODS

Twelve healthy male subjects performed computer work with passive (relax) and active (30% maximum voluntary contraction of shoulder elevation) pauses given every 40s over 2 days, before, immediately and 24h after eccentric exercise. Surface EMG signals were recorded from four parts of the trapezius during computer work.

FINDINGS

EMG amplitude during computer work decreased immediately after exercise (P<0.05). In the clavicular and descending parts of the trapezius, the centroid of exposure variation analysis along the time axis was lower during computer work with active pauses compared with passive ones (P<0.05). Further, lower values of relative rest time was observed during active pause (P<0.05).

INTERPRETATION

Eccentric exercises had a short term effect on muscle activation pattern during computer work, and decreased the muscle activity immediately after the exercises. The results of this study showed a more variable trapezius activity pattern and a lower trapezius rest with active pauses compared with passive pauses. Moreover, eccentric exercises resulted in a less variable activation pattern, decreasing the effect of active pauses.