Jamie Tallent

Exercise-induced muscle damage is reduced in resistance-trained males by branched chain amino acids: a randomized, double-blind, placebo controlled study

BackgroundIt is well documented that exercise-induced muscle damage (EIMD) decreases muscle function and causes soreness and discomfort. Branched-chain amino acid (BCAA) supplementation has been shown to increase protein synthesis and decrease muscle protein breakdown, however, the effects of BCAAs on recovery from damaging resistance training are unclear. Therefore, the aim of this study was to examine the effects of a BCAA supplementation on markers of muscle damage elicited via a sport specific bout of damaging exercise in trained volunteers.MethodsTwelve males (mean ± SD age, 23 ± 2 y; stature, 178.3 ± 3.6 cm and body mass, 79.6 ± 8.4 kg) were randomly assigned to a supplement (n = 6) or placebo (n = 6) group. The damaging exercise consisted of 100 consecutive drop-jumps. Creatine kinase (CK), maximal voluntary contraction (MVC), muscle soreness (DOMS), vertical jump (VJ), thigh circumference (TC) and calf circumference (CC) were measured as markers of muscle damage. All variables were measured immediately before the damaging exercise and at 24, 48, 72 and 96 h post-exercise.ResultsA significant time effect was seen for all variables. There were significant group effects showing a reduction in CK efflux and muscle soreness in the BCAA group compared to the placebo (P<0.05). Furthermore, the recovery of MVC was greater in the BCAA group (P<0.05). The VJ, TC and CC were not different between groups.ConclusionThe present study has shown that BCAA administered before and following damaging resistance exercise reduces indices of muscle damage and accelerates recovery in resistance-trained males. It seems likely that BCAA provided greater bioavailablity of substrate to improve protein synthesis and thereby the extent of secondary muscle damage associated with strenuous resistance exercise. Clinical Trial Registration Number: NCT01529281.

Assessment of eccentric exercise-induced muscle damage of the elbow flexors by tensiomyography

Exercise induced muscle damage (EIMD) impairs maximal torque production which can cause a decline in athletic performance and/or mobility. EIMD is commonly assessed by using maximal voluntary contraction (MVC), creatine kinase (CK) and muscle soreness. We propose as an additional technique, tensiomyography (TMG), recently introduced to measure mechanical and muscle contractile characteristics. The purpose of this study was to determine the validity of TMG in detecting changes in maximal torque following EIMD. Nineteen participants performed eccentric elbow flexions to achieve EIMD on the non- dominant arm and used the dominant elbow flexor as a control. TMG parameters, MVC and rate of torque development (RTD) were measured prior to EIMD and repeated for another six consecutive days. Creatine kinase, muscle soreness and limb girth were also measured during this period. Twenty four hours after inducing EIMD, MVC torque, RTD and TMG maximal displacement had significantly (p<0.01) declined by 37%, 44% and 31%, respectively. By day 6 MVC, RTD and TMG recovered to 12%, 24% and 17% of respective pre-EIMD values. In conclusion, as hypothesised TMG maximal displacement significantly followed other standard EIMD responses. This could therefore be useful in detecting muscle damage from impaired muscle function and its recovery following EIMD.

Repeatability of Corticospinal and Spinal Measures during Lengthening and Shortening Contractions in the Human Tibialis Anterior Muscle

Elements of the human central nervous system (CNS) constantly oscillate. In addition, there are also methodological factors and changes in muscle mechanics during dynamic muscle contractions that threaten the stability and consistency of transcranial magnetic stimulation (TMS) and perpherial nerve stimulation (PNS) measures. Purpose To determine the repeatability of TMS and PNS measures during lengthening and shortening muscle actions in the intact human tibialis anterior. Methods On three consecutive days, 20 males performed lengthening and shortening muscle actions at 15, 25, 50 and 80% of maximal voluntary contraction (MVC). The amplitude of the Motor Evoked Potentials (MEPs) produced by TMS was measured at rest and during muscle contraction at 90° of ankle joint position. MEPs were normalised to Mmax determined with PNS. The corticospinal silent period was recorded at 80% MVC. Hoffman reflex (H-reflex) at 10% isometric and 25% shortening and lengthening MVCs, and V-waves during MVCs were also evoked on each of the three days. Results With the exception of MEPs evoked at 80% shortening MVC, all TMS-derived measures showed good reliability (ICC = 0.81–0.94) from days 2 to 3. Confidence intervals (CI, 95%) were lower between days 2 and 3 when compared to days 1 and 2. MEPs significantly increased at rest from days 1 to 2 (P = 0.016) and days 1 to 3 (P = 0.046). The H-reflex during dynamic muscle contraction was reliable across the three days (ICC = 0.76–0.84). V-waves (shortening, ICC = 0.77, lengthening ICC = 0.54) and the H-reflex at 10% isometric MVC (ICC = 0.66) was generally less reliable over the three days. Conclusion Although it is well known that measures of the intact human CNS exhibit moment-to-moment fluctuations, careful experimental arrangements make it possible to obtain consistent and repeatable measurements of corticospinal and spinal excitability in the actively lengthening and shortening human TA muscle.

Corticospinal responses of resistance-trained and un-trained males during dynamic muscle contractions

Little is known regarding the modulation and the plasticity of the neural pathway interconnecting elements of the central nervous system and skeletal muscle in resistant-trained individuals. The aim of the study was to compare corticospinal and spinal responses measured during dynamic muscle contractions of the tibialis anterior in resistance trained (RT) and un-trained (UT) males. Nine UT and 10 RT male volunteers reported to the laboratory 24h following a familiarisation session. Motor evoked potentials (MEPs) and the cortical silent period were evoked using transcranial magnetic stimulation at a range of contraction intensities and was delivered as the ankle passed 90° during shortening and lengthening contractions. The Hoffmann reflex (H-reflex) and V-waves were evoked with peripheral nerve stimulation. Despite the RT group being significantly stronger during shortening (28%; P=0.023: CI=1.27-15.1Nm), lengthening (25%; P=0.041: CI=0.27-17.0Nm) and isometric muscle actions (20%; P=0.041; CI=0.77-14.9Nm), no differences between the groups existed for corticospinal or spinal variables. Lack of detectable differences between RT and UT individuals may be linked to minimal exposure to task specific, isolated high intensity resistance training of the TA muscle.

Recovery time of motor evoked potentials following lengthening and shortening muscle action in the tibialis anterior

Motor evoked potentials (MEP) at rest remain facilitated following an isometric muscle contraction. Because the pre-synaptic and post-synaptic control of shortening (SHO) and lengthening (LEN) contractions differs, the possibility exists that the recovery of the MEP is also task specific. The time course of MEP recovery was assessed in the tibialis anterior following SHO and LEN (0.26 rad/s) at 25% and 80% of maximal voluntary contraction. Following LEN and SHO contractions, the MEP recovered to baseline levels within 10s. Despite task-specific differences between SHO and LEN contractions, the MEP facilitation from the augmented neurotransmitter release appears to be short lasting and not influenced by contraction type.

The role of neural tension in stretch-induced strength loss.

Abstract McHugh, MP, Tallent, J, and Johnson, CD. The role of neural tension in stretch-induced strength loss. J Strength Cond Res 27(5): 1327–1332, 2013—The purpose of this study was to determine if neural tension during passive stretching affected subsequent strength loss. Eleven healthy subjects (10 men, 1 woman; age 34 ± 12 years) performed maximal isometric hamstring contractions at 100°, 80°, 60°, and 40° knee flexion before and after five 1-minute hamstring stretches performed in either a spinal neutral position or a neural tension position. One leg was stretched in the neutral position and the other in the neural tension position. Hamstring electromyography (EMG) activity was recorded during all contractions and stretches. Passive resistance to stretch was reduced by 11% after stretching (p < 0.01; no difference between neutral or neural tension stretches p = 0.41). Stretch-induced strength loss was apparent after neural tension stretches (12%, p < 0.01) but not after neutral stretches (5%, p = 0.09). There was a rightward shift in the angle-torque curve after neutral stretches (strength loss on ascending limb, strength gain on descending limb, p < 0.01). This effect was not apparent after neural tension stretches (p = 0.43). Stretching did not affect EMG activity during isometric contractions (<2% decline p = 0.58; no difference between neutral and neural tension, p = 0.86). Hamstring stretching with the spine in a neutral position did not result in a significant strength loss but shifted the length-tension relationship such that strength was decreased at short muscle lengths and increased at long muscle lengths. Hamstring stretching with increased neural tension resulted in strength loss with no associated shift in the length-tension relationship.

Enhanced Corticospinal Excitability and Volitional Drive in Response to Shortening and Lengthening Strength Training and Changes Following Detraining

There is a limited understanding of the neurological adaptations responsible for changes in strength following shortening and lengthening resistance training and subsequent detraining. The aim of the study was to investigate differences in corticospinal and spinal responses to resistance training of the tibialis anterior muscle between shortening or lengthening muscle contractions for 4 weeks and after 2 weeks of detraining. Thirty-one untrained individuals were assigned to either shortening or lengthening isokinetic resistance training (4 weeks, 3 days/weeks) or a non-training control group. Transcranial magnetic stimulation and peripheral nerve stimulation (PNS) were used to assess corticospinal and spinal changes, respectively, at pre-, mid-, post-resistance training and post detraining. Greater increases changes (P < 0.01) in MVC were found from the respective muscle contraction training. Motor evoked potentials (expressed relative to background EMG) significantly increased in lengthening resistance training group under contraction intensities ranging from 25 to 80% of the shortening and lengthening contraction intensity (P < 0.01). In the shortening resistance training group increases were only seen at 50 and 80% of both contraction type. Volitional drive (V-wave) showed a greater increase following lengthening resistance training (57%) during maximal lengthening contractions compared to maximal shortening contractions following shortening resistance training (23%; P < 0.001). During the detraining period MVC and V-wave did not change (P > 0.05), although MEP amplitude decreased during the detraining period (P < 0.01). No changes in H-reflex were found pre to post resistance training or post detraining. Modulation in V-wave appeared to be contraction specific, whereby greatest increases occurred following lengthening resistance training. Strength and volitional drive is maintained following 2 weeks detraining, however corticospinal excitability appears to decrease when the training stimulus is withdrawn.

Quantification of bowling workload and changes in cognitive function in elite fast bowlers in training compared with twenty20 cricket.

BACKGROUND Bowling overs are the primary recorded measure for workloads in cricket for youth through to professionals. However, the validity of this measure has never been tested. Additionally, despite the cognitive component of cricket being suggested to be very high, changes in psychomotor processing speed has again not been explored. METHODS Eight professional English county cricket bowlers participated in the study. Participants wore global positioning systems with a tri-axial accelerometer during a Twenty20 match and training. Bowling overs were expressed relative to external forces. Additionally, cognitive function (as measured by psychomotor speed) was assessed pre and post Twenty20 game and training. RESULTS When expressed relative to high intensity running distance or external forces from the tri-axial accelerometer, the cost of each over (6 deliveries) was over 100% higher in a Twenty20 game compared to training. Psychomotor speed was unchanged although error within the cognitive task increased post Twenty20 (391±82±547±104 ms) and training (414±110±561±238 ms). This data suggests that reaction time is unchanged from cricket but the chance of making the incorrect decision is increased. CONCLUSIONS Movements in fielding should be quantified or bowling workloads adjusted to account for the high intensity fielding associated with Twenty20 cricket. Cognitive function was impaired following bowling, suggesting practitioners may also monitor psychomotor changes when assessing fatigue and allow appropriate time to mentally recover.

Role of neural tension in stretch-induced strength loss

The aim of the study was to examine whether increased neural tension during passive hamstring stretching contributes to stretch-induced strength loss. Eleven healthy subjects performed maximal isometric knee flexion contractions (100°, 80°, 60° and 20°) before and after a series of hamstring stretches (six 1-min stretches), performed in either a spinal neutral position or a neural tension position. Effect of stretch technique (neutral or neural tension) on passive resistance to stretch, strength-induced strength loss and electromyography activity during strength tests was assessed with repeated measures analysis of variance. Passive resistance to stretch was reduced by 19% after the series of stretches (p=0.001) with no difference between neutral or neural tension stretches (p=0.41). Stretch-induced strength loss was greater (p=0.043) after the neural tension stretches (13%) vs the neutral stretches (5%). There was an apparent rightward shift in the length tension curve after neutral stretches with a 15% strength loss at muscle lengths shorter than optimum, and a 10% gain in strength at muscle lengths longer than optimum (p<0.001). This effect was not apparent after neural tension stretches where strength loss was 21% at muscle lengths shorter than optimum and 9% at muscle lengths longer than optimum. The addition of neural tension to hamstring stretching increased stretch-induced strength loss but this was not associated with observable neural inhibition. The absence of a rightward shift in the length-tension curve after neural tension stretching indicates that muscle fibre shortening during isometric contractions was unaffected, presumably because tendon-aponeurosis compliance was not increased.