Isokinetic Research Articles

Relationship Between Strength And Power In Elite Short Track Speed Skaters

PURPOSE: To examine the relationship between strength and power in elite short track speed skaters. METHODS: Ten males (mean ± SD; age 21.1 ± 1.9 y; height = 177.2 ± 5.3 cm; mass = 71.3 ± 4.8 kg) and five females (age 22.8 ± 1.3 y; height 169.1 ± 4.3 cm; mass = 60.4 ± 1.3 kg) elite short track speed skaters volunteered and consented to an IRB approved informed consent to participate. Anthropometric measurements were recorded followed by a dynamic warm-up. The athletes completed four assessments: isometric (ISOM) torque, isokinetic (ISOK) torque, vertical jump (VJ), and Wingate testing. An isokinetic dynamometer was used to assess ISOM and ISOK torque for both right and left knee extensors and flexors. For ISOK torque, participants completed one set of five repetitions at a velocity of 60°/s. ISOM assessment used a stationary 60-degree knee angle, where participants completed three repetitions for three seconds each. Peak torque for quadriceps (QUAD) and hamstrings (HAM) for both right leg (RL) and left leg (LL) were used for analysis. The VJ test was completed on an AMTI force plate, where peak power (PP) output was used for analysis. Lastly, participants conducted a Wingate anaerobic cycling test at a load of 9 g/kg of body mass, where PP output was used for analysis. SPSS 24 was used to analyze Pearson r correlations between strength and power variables. RESULTS: There was a moderately strong significant (p = 0.006) correlation (r = .669) between VJ PP and ISOK RL HAM PT. There was a moderately strong significant correlation between Wingate PP and ISOK LL QUAD PT (p = 0.004; r = .695) and ISOK RL HAM PT (p = 0.002; r = .721). There was a moderate significant correlation between Wingate PP and ISOK RL QUAD PT (p = 0.029; r = .562), ISOK LL HAM PT (p = 0.028; r = .565), and ISOM LL QUAD PT (p = 0.037; r = .542). CONCLUSIONS:Short track speed skaters train to focus on repeatable explosive movement during competition which corresponds to their lower extremity strength. During a race, short track speed skaters’ LL is in a more fixed position while the RL is isokinetically moving, which relates to our findings that the ISOM LL QUAD was correlated with PP and RL HAM and QUAD ISOK were correlated with PP. Practitioners may use this as a reference to gain insight on the benefits of training for power and strength to enhance performance.

Exploring the interaction between lactoferrin and CdTe quantum dots: Energetic and molecular dynamic study

The kinetic and energetic characterization of interactions between quantum dots (QDs) and proteins is fundamental for understanding the toxicity and effectiveness of these nanoparticles in therapeutic applications. In this study, we combined kinetic and thermodynamic data from surface plasmon resonance (SPR) and isothermal titration microcalorimetry (ITC) to explore the complexation mechanism between thioglycolic acid-capped cadmium telluride QD (CdTe@TGA) and bovine lactoferrin (LF) under physiological conditions. The SPR results demonstrated that QD binds to LF forming a 1:1 [LF-CdTe@TGA]° thermodynamically stable complex, whose binding constant (KbSPR) ranged from 7.18 × 104 to 6.75 × 104 M−1. The association rate constant (ka) values were in the order of 103 M−1 s−1 while the complex residence time (tR) was ∼70 s. The formation of both [LF-CdTe@TGA]° and [LF-CdTe@TGA]‡ activated complexes occurred with the compensation of the enthalpic and entropic terms with the increase in temperature, characterizing enthalpy–entropy compensation (EEC), and iso-kinetic (IC) compensation, respectively. Using ITC, we also found the formation of a 1:1 [LF-CdTe@TGA]° complex, but the calculated KbITC values were on the order of 107 L mol−1. Again, we found that the formation of [LF-CdTe@TGA]°was exothermic and entropically favorable at 298.15 K, although ΔHITC° (−20.46 kJ mol−1) and TΔSITC° (24.13 kJ mol−1) values were higher in magnitude than those found by SPR (ΔHSPR°=−17.35 kJ mol−1 and TΔSSPR° = 10.39 kJ mol−1). We believe that this fundamental study will provide new insights into the safe and effective application of QDs in biological and medical fields.

The Effects of Short-Term Resistance Training and Subsequent Detraining on Neuromuscular Function, Muscle Cross-Sectional Area, and Lean Mass

PurposeTo examine and compare the effects of three days of dynamic constant external resistance (DCER) and isokinetic (ISOK) training and subsequent detraining on thigh muscle cross-sectional area (TMCSA) and thigh lean mass (TLM), ISOK peak torque (PT), DCER strength, isometric force, muscle activation, and percent voluntary activation (%VA).MethodsThirty-one apparently-healthy untrained men (mean ± SD age = 22.2 ± 4.2 years; body mass = 77.9 ± 12.9 kg; height = 173.9 ± 5.4 cm) were randomly assigned to a DCER training group (n = 11), ISOK training group (n = 10) or control (CONT) group (n = 10). Subjects visited the laboratory eight times. The first visit was a familiarization session, the second visit was a pre-training assessment, the subsequent three visits were for unilateral training of the quadriceps (if assigned to a training group), and the last three visits were the post-training assessments conducted at three days, one week, and two weeks after training ended.ResultsDCER strength increased from pre- to post-training assessment 1 in both limbs for the DCER group only, and remained elevated during post-training assessments 2 and 3 (P < 0.05). In addition, surface EMG for the biceps femoris was higher at post-training assessment 3 than at the pre-training assessment, and post-training assessments 1 and 2 (P < 0.05). No other training-related changes were found.ConclusionThe primary finding of this study was that DCER strength of the trained and untrained limbs can be increased with three days of training. This has important implications for injury rehabilitation, where in the initial period post-injury strength gains on an injured limb can possibly be obtained with short-term contralateral resistance training.

Does resistance training promote enough muscular strength increases to move weak older women to better strength categories?

We compared the magnitude of muscular strength changes among older women occupants of different strength tertiles in response to progressive resistance-training (RT). Additionally, we examined the possibility of older women initially characterized as weak (occupants of the lower tertile of strength status) can achieve a higher muscular strength level to be inserted into a better category (middle or upper tertiles). The present investigation was attended by 113 physically independent older women (>60years old). Muscular strength was assessed by one-repetition maximum (1RM) tests on chest press, preacher curl, leg extension exercises, and by the isokinetic (ISOK) peak torque of knee extension and flexion at 60 and 180°/s angular velocities. The RT lasted 12weeks (3 x/week) and consisted of eight exercises for the whole body. The participants were divided into tertiles (LOWER, MIDDLE, and UPPER) according to the performance at baseline for each strength measure. After RT, the LOWER tertile showed more significant magnitude gains than the UPPER tertile to the 1RM in leg extension and preacher curl and isokinetic measurements (6.9-36.3%). A considerable number of older women increased muscular strength enough to move from LOWER to MIDDLE or UPPER tertiles. From our results, it can be inferred that older women occupants of the lower strength tertile show more significant muscular strength gains when compared to their stronger counterparts. Moreover, 12weeks of RT seem to be sufficient to transfer older women previously characterized as "weak" to a better category.

Effects of Pre-Sleep Whey vs. Plant-Based Protein Consumption on Muscle Recovery Following Damaging Morning Exercise.

Pre-sleep whey protein intake has been shown to improve overnight muscle protein synthesis, muscle size and strength, and muscle recovery. Despite a growing interest in alternative protein sources, such as plant-based protein, there is no evidence regarding the efficacy of plant-based proteins consumed pre-sleep. Therefore, we aimed to compare whey vs. plant-based pre-sleep protein dietary supplementation on muscle recovery in middle-aged men. Twenty-seven recreationally active, middle-aged men performed 5 sets of 15 repetitions of maximal eccentric voluntary contractions (ECC) for the knee extensors (ext) and flexors (flex), respectively, in the morning. Participants consumed 40 g of either whey hydrolysate (WH, n = 9), whey isolate (WI, n = 6), rice and pea combination (RP, n = 6), or placebo (PL, n = 6) 30 min pre-sleep on the day of ECC and the following two nights. Catered meals (15% PRO, 55% CHO, 30% Fat) were provided to participants for 5 days to standardize nutrition. Plasma creatine kinase (CK), interleukin-6 (IL-6), and interleukin-10 (IL-10) were measured at pre, immediately post (+0), +4, +6, +24, +48, and +72 h post-ECC. Isometric (ISOM) and isokinetic (ISOK) maximal voluntary contraction force were measured at pre, immediately post (+0), +24, +48, and +72 h post-ECC. Muscle soreness, thigh circumference, and HOMA-IR were measured at pre, +24, +48, and +72 h post-ECC. CK was increased at +4 h post-ECC, remained elevated at all time points compared to baseline (p < 0.001), and was significantly greater at +72 h compared to all other time points (p < 0.001). IL-6 was increased at +6 h (p = 0.002) with no other time differing from baseline. ISOMext was reduced after ECC (p = 0.001) and remained reduced until returning to baseline at +72 h. ISOMflex, ISOKext, and ISOKflex were reduced after ECC and remained reduced at +72 h (p < 0.001). Muscle soreness increased post-ECC (p < 0.001) and did not return to baseline. Thigh circumference (p = 0.456) and HOMA-IR (p = 0.396) did not change post-ECC. There were no significant differences between groups for any outcome measure. These data suggest that middle-aged men consuming 1.08 ± 0.02 g/kg/day PRO did not recover from damaging eccentric exercise at +72 h and that pre-sleep protein ingestion, regardless of protein source, did not aid in muscle recovery when damaging eccentric exercise was performed in the morning.

Charge Carrier Transport in a Polymeric Semiconductor: Poly(3-hexylthiophene-2,5-diyl) (P3HT)

Organic semiconductors are now widely employed in electronic and optoelectronic devices due to their solution processability and compatibility with flexible substrates. 1 The Meyer Neldel (MN) Rule or isokinetic (IK) law means that a set of comparable samples exhibit kinetic behavior independent of activation energy at an IK or MN temperature.2 It is obeyed by the electron or hole mobility, µ, in many organic semiconductors, including pentacene3, fullerene4, N-Alkyl Perylene Diimides,5 etc. The existence of MNR is still not widely known. Further, despite considerable evidence in its favor, the multi-excitation entropy (MEE) model of its origin is still frequently contested. We fabricated organic field effect transistors (FETs) based on regioregular poly(3-hexylthiophene-2,5-diyl) (RR P3HT) of three different values of molecular weight, MW, and studied the dependence of the mobility, µ, upon the gate bias, Vg , and temperature, T. For all values of MW, we found that in the range 200 to 290 K (low T), the µ of the FET carriers exhibits an exponential dependence upon 1/T for different Vg , with an MN temperature about 290K. Between this temperature and 350K (high T), µ increases more rapidly than it did below, and is independent of Vg . We believe that, in the low T regime, the polaronic carriers hop along the polymer backbone chain. We attribute the high temperature behavior to the alpha relaxation of the polymers, that is to the movement of the backbone chains. We believe that in this regime, the polaronic carriers move with the mobile chains. We have also observed the effect of source-drain voltage upon µ.Reference 1. F. Cicoira and C. Santato, Organic Electronics: Emerging Concepts and Technology, Wiley-VCH Verlag GmbH & Co. KGaA, 2013, Germany.2. A. Yelon, et al., Multi-excitation entropy: its role in thermodynamics and kinetics, Rep. Prog. Phys., 69, 1145-1194, 2006.3. E. J. Meijer, et al., The Meyer–Neldel rule in organic thin-film transistors, Appl. Phys. Lett., 76, 3433, 2000.4. J. C. Wang and Y. F. Chen, The Meyer–Neldel rule in fullerenes, Appl. Phys. Lett., 73, 948 1998.5. R. J. Chesterfield, et al., Organic Thin Film Transistors Based on N-Alkyl Perylene Diimides: Charge Transport Kinetics as a Function of Gate Voltage and Temperature, J. Phys. Chem. B, 108, 19281-19292, 2004.

Postural balance, muscle strength, and history of falls in end-stage renal disease patients living with a kidney transplant: A cross-sectional study

BackgroundEnd-stage renal disease patients living with a kidney transplant (KT) often present with frailty, functional disability, and mobility impairments that may result in a high risk of falls. Postural balance and muscle strength are implicated in the etiology of falls in the geriatric population, and both may be impaired in KT patients. Research questionWe conducted a cross-sectional investigation to estimate the prevalence of falls, as well as to explore the association between postural balance, muscle strength and history of falls in end-stage renal disease patients living with a KT. MethodsFifty-nine prevalent KT patients (age = 53.2 ± 11 years) were enrolled in this cross-sectional study. Participants were classified as fallers/non-fallers and underwent an objectively-measured assessment of postural balance on a stabilometric platform in eyes open (EO), eyes closed (EC), and dual-task (DT) conditions. Center of pressure (CoP) variables were taken for the analysis. In addition, participants underwent isometric (IM) and isokinetic (IK) assessments of lower limb muscle strength on a multi-joint evaluation system. ResultsThirty-four percent of the study participants reported at least one fall in the previous 12 months. In logistic regression analysis, CoP velocity in EO (OR: 1.23, 95 % CI: 1.06–1.43, p = .007), and IK ankle dorsiflexion strength (OR: 0.87, 95 % CI: 0.77-0.99, p = .034) were independently associated with increased odds of falling. SignificanceThis cross-sectional study indicates that patients living with a KT presented with a prevalence of falls indicative of a high risk of falling. Postural balance and muscle strength are exercise-modifiable factors and further research is warranted to establish to what extent these measures may be implicated in the etiology of falling in this patient group.

Consecutive, Resting, Long-Duration Hyperoxic Exposures Alter Neuromuscular Responses During Maximal Strength Exercises in Trained Men.

Purpose: The main objective of this study was to investigate the physiological effects of repetitive diving-induced hyperoxic conditions at 1.35 atmospheres absolute (ATA) on neuromuscular strength performance. We hypothesized that following five days of consecutive, resting, long-duration (6 h or more) hyperoxic water immersions (WIs) neuromuscular strength performance would be reduced with a longer recovery time in comparison to previously reported normoxic WIs.Methods: Thirteen (n = 13) active male divers [31.3 ± 1.7 (24–43) years, mean ± years] completed five consecutive days of 6-h resting WIs with 18-h surface intervals while breathing 100% O2 (n = 13) at 1.35 ATA. Skeletal muscle performance assessments occurred immediately before and after each WI and 24 and 72 h after the final WI. Performance assessments included maximum voluntary isometric contraction (MVIC) and maximal isokinetic (IK) knee extensions and elbow flexions, and isometric maximum handgrip (MHG) strength. Neuromuscular activation was also measured on the quadriceps, biceps brachii, and brachioradialis via surface electromyography (sEMG).Results: MHG declined by 7.8% (p < 0.001) by WI 5 with performance returning to baseline by 24-h post-WI. Brachioradialis neuromuscular activation increased by 42% on WI 5. MVIC knee extension performance dropped by 4% (p = 0.001) on WI 3 with a 11% overall decrease in quadriceps neuromuscular activation. Maximal IK knee extension dropped by 3.3% on WI 5 with 9% drop in overall quadriceps activation during the same period. MVIC elbow flexion declined by 5.1% on WI 5 but returned to baseline by 72-h post-WI. Maximal IK elbow flexion performance dropped by 8.6% on WI 5 with a continual decline in biceps brachii neuromuscular activation of 24% on WI 5.Conclusion: Consecutive, resting, long-duration hyperoxic WIs reduce muscular performance in multiple muscle groups and alter neuromuscular activation after 3 days of WI with performance adaptations recovering toward baseline by the end of the WI 5. However, neuromuscular activation remains decreased and appears to last beyond the 72-h post-WI recovery period.

Effects of Repeated, Long-Duration Hyperoxic Water Immersions on Neuromuscular Endurance in Well-Trained Males.

PurposeThis study examined the effects of repeated long-duration hyperoxic water immersions (WIs) at 1.35 atmospheres absolute (ATA) on neuromuscular endurance performance. We hypothesized that over a 5-day period of consecutive, resting, long-duration hyperoxic WIs there would be a decrease to neuromuscular endurance performance and tissue oxygenation with the quadriceps muscle, but not with the forearm flexors.MethodsThirteen well-trained, male subjects completed five consecutive 6-h resting WIs with 18-h surface intervals during the dive week while breathing 100% oxygen at 1.35 ATA. We assessed skeletal muscle endurance performance before and after each WI, and 24 and 72 h after the final WI. Muscular endurance assessments included 40% maximal handgrip endurance (MHE) and 50-repetition maximal isokinetic (IK) knee extensions. Near-infrared spectroscopy (NIRS) was used to measure muscle oxidative capacity (MOC) of the vastus lateralis and localized muscle tissue oxygenation of the vastus lateralis and flexor carpi radialis. Simultaneously, we measured brachioradialis neuromuscular activation by surface electromyography (SEMG).ResultsMHE time-to-fatigue performance declined by 15% at WI 3 (p = 0.009) and by 17% on WI 5 (p = 0.002). Performance continued to decline by 22% at 24-h post-WI (p < 0.001) and by 12% on 72-h post-WI (p = 0.019). Fifty-repetition IK knee extension total work decreased by 5% (p = 0.002) on WI 3, and was further reduced by 7.5 and 12.3% (p = 0.032) at pre-WI 5 and 24-h post-WI, respectively. However, the rate of fatigue was 8 (p = 0.033) and 30% (p = 0.017) lower at WI 3 and 24-h post-WI when compared to WI 1, respectively, demonstrating the muscles were still fatigued from the previous hyperoxic WIs. We detected no significant limitations in oxygen off-loading kinetics during the exercise or MOC measurements.ConclusionRepeated, resting, long-duration hyperoxic WIs caused significant reductions to muscular endurance but not to indirect measures of oxygen kinetics in load bearing and non-load bearing muscles.

Consecutive, Long-Duration Hyperoxic Immersions Effect on Skeletal Muscle Performance in Well Trained, Male Divers

PURPOSE: The primary objective of this study was to investigate how resting, long-duration hyperoxic water immersions (WI)s at 1.35 atmospheres absolute (ATA) effected neuromuscular strength performance. We hypothesized that following five consecutive days of hyperoxic WIs, neuromuscular strength performance would be diminished post-WI and remain reduced longer than 72-hrs post-WI. METHODS: Thirteen (n=13), active male divers [31.3 ± 1.7 (24-43) yrs., mean ± SEM] completed five consecutive 6-hour resting WIs with 18-hour surface intervals while breathing 100% O2 (n=13) at 1.35 ATA. Skeletal muscle performance assessments occurred immediately before and after each WI, and 24 and 72 hours after the final WI. Performance assessments included maximum voluntary isometric contraction (MVIC) and maximal isokinetic (IK) knee extensions and elbow flexions, and maximum handgrip strength (MHG). We measured neuromuscular activation of the quadriceps, biceps brachii, and brachioradialis via surface electromyography (sEMG). RESULTS: MHG declined by 7.8% (p<0.001) by WI 5 with performance returning to baseline by 24-hr post-WI. Brachioradialis neuromuscular activation increased by 42% (p<0.001) on WI 5. MVIC knee extension performance dropped by 4% (p=0.001) on WI 3 with an 11% overall decrease in quadriceps neuromuscular activation. Maximal IK knee extension dropped by 3.3% (p=0.008) on WI 5 with 9.3% (p=0.014) drop in overall quadriceps activation dropped by 7% (p=0.013) during the same period. MVIC elbow flexion performance declined by 5.1% (p<0.001) with an 18% decline in neuromuscular activation by WI 5 but returned to baseline by 72-hr post-WI. Maximal IK elbow flexion performance dropped by 8.6% (p<0.001) on WI 5 with a continual decline in biceps brachii neuromuscular activation by 24% (p<0.001) on WI 5. CONCLUSION: The decreases in neuromuscular activation and strength performance coinciding with the non-load bearing muscles affected more than the load-bearing muscles. Yet, the brachioradialis had increases in neuromuscular activation with decreases in performance. These types of hyperoxic WIs caused significant changes to neuromuscular performance after three days of WI with recovery varying with each measured variable with some decrements lasting until the 72-hr post-WI recovery period.

Effects of repeated long-duration water immersions on skeletal muscle performance in well-trained male divers.

The objective of this study was to examine the effects of repeated long-duration water immersions (WI)s at 1.35 atmospheres absolute (ATA) on neuromuscular performance in load bearing and non-load bearing muscle groups. During a dive week (DW), fifteen well-trained male divers completed five consecutive 6-h resting dives with 18-h surface intervals while breathing compressed air at 1.35 ATA. Skeletal muscle performance assessments occurred immediately before and after each WI, and 24 and 72h after the final WI. Exercise assessments included maximum voluntary isometric contraction (MVIC), maximal isokinetic (IK) contraction, maximum handgrip strength (MHG). Surface electromyography measured neuromuscular activation of the quadriceps, biceps brachii (BB), and brachioradialis. MVIC torque of knee extensors and BB decreased by 6% (p = 0.001) and 2% (p = 0.014), respectively, by WI 3. Maximal IK torque of knee extensors increased by 11 and 5% post-WI on WIs 3 and 5 (p < 0.001) with greater neuromuscular activation post-WI than pre-WI (p < 0.001). Maximum IK elbow flexion torque did not change throughout the DW with BB neuromuscular activation greater post-WI than pre-WI (p < 0.001). MHG force output was 4% greater post-WI than pre-WI (p < 0.001) with increased brachioradialis activation through 72-h post-WI (p < 0.001). All muscle performance metrics returned baseline levels by 72-h post-WI. Our findings indicate that repeated WIs caused noticeable decrements in neuromuscular activation and performance of load bearing muscles on WI 3 while full recovery was observed by 72-h post-WI.

The Relationship Of Cognitive Scores With Muscle Power, Strength, And 6-minute Walk In Breast Cancer Survivors

The relationship between cognition and aerobic fitness is well studied in breast cancer survivors (BCS); however, there is a lack of research evaluating the relationships between cognition and anaerobic fitness. PURPOSE: This study examined the relationship between cognition, muscle power, strength, and the 6-min walk (6MW) in BCS. METHODS: Forty-four BCS (60±8 yrs; BMI: 29.9±6.5 kg/m2) completed Trail-Making Test A and B [TMTA (processing speed), TMTB (executive function)], Digit Span Forward (attention) and Backward (working memory), and Controlled Oral Word Association Test [COWAT (executive function)] to assess cognitive domains. Lower body isokinetic (ISK) power and strength were assessed by the Biodex™. Endurance was assessed by the 6MW. Pearson product-moment correlations were used to evaluate relationships between cognition and anaerobic fitness. Significance was accepted at p≤0.05. RESULTS: Faster TMTA and TMTB scores were correlated with greater ISK average power for extension at 60 degrees/sec (TMTA: r=-0.40; TMTB: r=-0.31) and 180 degrees/sec (TMTA: r=-0.45; TMTB: r=-0.30) while TMTA was correlated with greater ISK average power for extension at 120 degrees/sec (r=-0.34). A subcategory of the COWAT was correlated with greater 6MW distance (r=0.31) and greater ISK average power for extension at 180 degrees/sec (r=0.30). CONCLUSION: Higher cognitive functioning, specifically processing speed and executive function domains, may be correlated to greater average power. These findings warrant more research on the benefits of power and strength training on cognition in BCS.

Effects of Consecutive, Long‐Duration Hyperoxic Water Immersions on Neuromuscular Performance in Well Trained, Male Divers

PURPOSEThe main objective of this study was to investigate the physiological effects of single and repetitive diving‐induced hyperoxic conditions on neuromuscular performance at 1.35 atmospheres absolute (ATA). We hypothesized that following five days of consecutive, resting, long‐duration hyperoxic water immersion (WI)s, neuromuscular performance would be reduced with a longer recovery period in comparison to normoxic WIs at 1.35 ATA.METHODSThroughout a dive week (DW), twenty‐eight healthy, active male divers [30±1 (24–43)years; mean ± SEM] completed five consecutive 6‐hour resting WIs with 18‐hour surface intervals while breathing compressed atmospheric air (Air: n=15) or 100% oxygen(O2:n=13) at 1.35 ATA. Skeletal neuromuscular performance was assessed immediately before and after each WI, and 24 and 72 hours after the final WI. Assessments included knee extension and elbow flexion maximum voluntary isometric contractions (MVIC) and maximal isokinetic (IK) contractions, as well as measurement of maximum handgrip strength (MHG). Simultaneously, surface electromyography (sEMG) amplitude of the vastus lateralis, rectus femoris, vastus medialis, biceps brachii, and brachioradialis was measured.RESULTSSignificant decreases were seen in maximal strength performance on WI 3 (MVIC knee extension: 3.4%, p&lt;0.001; O2: 4.3%, p=0.016; MVIC elbow flexion: 3.5%, p=0.002, combined group result) with recovery occurring by WI5. The O2 group knee extensor neuromuscular activation decreased by 10% throughout the DW and remained reduced by 14% through the 72‐hr post‐WI. The Air group neuromuscular activation increased throughout the DW but returned to baseline by 72‐hr post‐dive. Combined group maximal IK elbow flexion and MHG strength performance decreased by 4% and 5%, respectively, throughout the DW (WI1&gt; WI3 and WI5, p&lt;0.001).CONCLUSIONConsecutive, resting, long‐duration normoxic WIs cause noticeable decrements in muscular strength performance after three days of WIs with recovery seen by 24‐hr post‐WI. Hyperoxic WIs caused significant reductions to neuromuscular activation. Future research should examine the causes of hyperoxia‐induced decreased neuromuscular activity.Support or Funding InformationOffice of Naval Research (ONR) Award Number N000141612112 and NAVSEA DSBDP N0002416WX02277This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Do isometric, isotonic and/or isokinetic strength trainings produce different strength outcomes?

IntroductionSeveral studies have been developed to determine which type of muscular action (isometric, isotonic and isokinetic) elicits more gains in functional strength and muscle mass. The comparisons between training outcomes are inconclusive due to lack of exercise standardization. ObjectiveTo compare muscle strength, mass, and functional performance in response to isometric, isotonic, and isokinetic contractions, when training loads (volume and intensity) are equated. MethodData were derived from a university community-recruited sample (n = 31 men). InterventionsUntrained men were assigned to isotonic (IT), isometric (IM), or isokinetic (IK) group, and trained their dominant quadriceps muscle 3 sessions/week for 8 weeks with a dynamometer. Muscle strength was assessed using Cybex 6000 dynamometer; the triple-hop-distance test was used to assess functional performance, and dual energy x-ray absorptiometry to assess lean muscle mass. ResultsAfter training, muscle lean muscle mass increased in isometric (+3.1%, p < 0.01) and isotonic groups (+3.9%, p < 0.01); only the isokinetic group showed a significant improvement in the triple-hop-distance test (4.84%, p < 0.01). ConclusionClinicians should consider isometric training as an alternative for isotonic training to gain muscle mass, and isokinetic training to improve functional performance of daily activities and/or sports.

Effects of Consecutive, Long-Duration Water Immersions on Skeletal Muscle Performance in Well Trained, Male Divers

PURPOSE: Diving operations may require personnel to be immersed for extended periods while breathing compressed air. The objective of this study was to examine the effects of resting, consecutive long-duration water immersion (WI)s at 1.35 atmospheres absolute (ATA) on neuromuscular performance in multiple muscle groups. We hypothesized a decrease in neuromuscular performance will occur following five days of consecutive, resting, long-duration WIs. METHODS: Fifteen healthy, active male divers completed five consecutive 6-hour resting dives with 18-hour surface intervals while breathing compressed air at 1.35 ATA. Skeletal muscle performance was assessed immediately before and after each WI, and 24 and 72 hours after the final WI. Assessments included maximum voluntary isometric contractions (MVIC), maximal isokinetic (IK) contractions, maximum handgrip (MHG), and surface electromyography (sEMG) of the vastus lateralis, rectus femoris, vastus medialis, biceps brachii, and brachioradialis. RESULTS: MVIC knee extension peak torque decreased by 6% (p=0.001) with an associated 7% increase in rectus femoris activation (p=0.048) by day 3. IK knee extension peak torque increased by 11% and 5% post-WI compared to pre-WI on days 3 and 5 (p<0.001), respectively, with increased quadriceps sEMG activation (p<0.001). However, an overall 3% decrease in torque production occurred on day 5 (p=0.015). MVIC elbow flexion peak torque decreased by 2% (p=0.014) on day 3 with an associated 12% decrease in biceps brachii sEMG activation (p=0.001); both metrics fully recovered by day 5. Biceps brachii sEMG activation increased 3% and 9% during IK elbow flexion on days 3 and 5 (p<0.001), respectively, with no change in torque production. MHG force output decreased 5% and 2% on days 3 and 5 (p<0.001). Brachioradialis sEMG activation increased by 5% on day 3 (p=0.005) and remained elevated through 72-hr post-WI (p<0.001). All muscle performance metrics equaled or exceeded baseline levels by 72-hr post-WI. CONCLUSION: Consecutive, resting, long-duration WIs cause small, but noticeable decrements to neuromuscular activation and performance after three days of WI with an adaptation towards recovery by the end of the WI 5. Further analyses are required to determine the mechanisms involved.

Neuromuscular Changes and Damage after Isoload versus Isokinetic Eccentric Exercise.

This study compared the effects of isoload (IL) and isokinetic (IK) knee extensor eccentric exercises on changes in muscle damage and neuromuscular parameters to test the hypothesis that the changes would be different after IL and IK exercises. Twenty-two young men were paired based on their strength and placed in the IL (N = 11) or the IK (N = 11) group. The IL group performed 15 sets of 10 eccentric contractions with a 150% of predetermined one-repetition maximum load. The IK group performed 15 sets of several maximal eccentric contractions matched set by set for the total amount of work and mean angular velocity with the IL group. Muscle damage markers (voluntary isometric peak torque, muscle soreness, and creatine kinase activity) and neuromuscular variables (e.g., voluntary activation, H-reflex, M-wave, and evoked torque) were measured before, immediately after, and 24, 48, 72, and 96 h postexercise. Voluntary isometric peak torque decreased to the same extent (P = 0.94) in both groups immediately after (IL = -40.6% ± 13.8% vs IK = -42.4% ± 10.2%) to 96 h after the exercise (IL = -21.8% ± 28.5% vs IK = -26.7% ± 23.5%). Neither peak muscle soreness (IL = 48.1 ± 28.2 mm vs IK = 54.7 ± 28.9 mm, P = 0.57) nor creatine kinase activity (IL = 12,811 ± 22,654 U·L vs IK = 15,304 ± 24,739 U·L, P = 0.59) significantly differed between groups. H-reflex (IL = -23% vs IK = -35%) and M-wave (IL = -10% vs IK = -17%) significantly decreased immediately postexercise similarly between groups. The changes in muscle damage and neuromuscular function after the exercise are similar between IL and IK, suggesting that resistance modality has little effects on acute muscle responses.

Effects of 28-Day Beta-Alanine Supplementation on Isokinetic Exercise Performance and Body Composition in Female Masters Athletes

Beta-alanine (BA) supplementation increases exercise performance due to increases in the intramuscular lactate buffer, carnosine. Females are more sensitive to these increases and results are further pronounced in trained individuals. Baseline intramuscular carnosine levels also naturally decrease with age; therefore, trained older females may experience augmented benefits from BA supplementation. However, the ability of BA to increase lower-body isokinetic strength (ISO) in female masters athletes (MA) is unknown. The purpose of this study was to examine the longitudinal effects of BA supplementation on ISO, handgrip strength (HG), and body composition in female MA cyclists. Twenty-two subjects participated in this double-blind randomized study. Subjects were randomized into 2 groups (placebo [PLA] = 8 g dextrose; BA = 800 mg + 8 g dextrose) and supplemented 4 times per day for 28 days. ISO, HG, and body composition were evaluated at baseline and at the same day/time each week over the 28-day intervention. No differences existed between groups at baseline or at the 7, 14, and 21 days time points for any variables (p > 0.05). When evaluating ISO (isokinetic) after 28 days, total work performed during the final third of the assessment (24.0 vs. -16.8% change) in flexion and average peak torque (5.4 vs. 2.9% change) in extension were significantly increased from baseline in BA compared with PLA (p ≤ 0.05). No differences existed for HG or body composition after supplementation. Twenty-eight days of BA supplementation increased peak torque and work completed, indicating BA improves lower-body exercise performance in female MA.

Cross-education effect after unilateral eccentric-only isokinetic vs dynamic constant external resistance training

The aim of this study was to evaluate the effects of unilateral eccentric training using constant velocity or constant external load on untrained limb. Forty-nine participants were randomized in isokinetic (IK), dynamic constant external resistance (DCER) unilateral eccentric training or control groups. Knee-extension 1RM and isometric, eccentric and concentric knee extensors’ peak torques, as well as changes in vastus lateralis muscle thickness, fascicle length, pennation angle and quadriceps fat-free mass were measured. After training, both IK and DCER similarly increased over time 1RM (respectively, +3.6 kg, CI 95 % 0.6–6.5 and +4.3 kg, CI 95 % 1.6–6.9), concentric (respectively, +8.4 N/m, CI 95 % 0.0 to +16.4 and 9.8 CI 95 % 0.6–19.2), eccentric (respectively, +28.5 N/m, CI 95 % 11.0 to +46.0 and 21.1 CI 95 % 15.1–37.0), and isometric (respectively, +15.4 N/m, CI 95 % 0.7–30.0 and +13.9, CI 95 % 0.3–27.5) peak torques. No increase was found for vastus lateralis muscle thickness, fascicle length, pennation angle and quadriceps fat-free mass. Eccentric training was effective for inducing strength, but not structural, adaptations in untrained limb. Both in rehabilitation and training practice, use of easily available gym devices can be a good substitute for expensive and often unavailable isokinetic devices.

Unilateral eccentric resistance training: A direct comparison between isokinetic and dynamic constant external resistance modalities

Aim of the study was to compare the effects of unilateral eccentric-only training using constant velocity vs. constant external load. Forty-seven participants were randomized in isokinetic (IK), dynamic constant external resistance (DCER) unilateral eccentric training or control groups. Knee extension 1RM and isometric, eccentric and concentric knee extensors peak torque, as well as changes in vastus lateralis fascicle pennation angle, fascicle length, muscle thickness, and quadriceps fat-free mass were measured. Both IK and DCER training consisted in 5 × 8 eccentric-only repetitions, 2d/w, for 6 weeks. IK and DCER training sessions were matched for total volume. After training, both IK and DCER similarly increased 1RM (respectively, +4.4 kg, CI95% 1.8–7.0 and +5.5 kg, CI95% 3.3–7.9), isometric (respectively, +34.5 N/m, CI95% 23.0–45.9 and +15.8, CI95% 5.4–26.2) and concentric peak torque (respectively, +17.0 N/m, CI95% 6.6 to +27.4 and 12.2 CI95% 2.8–21.7). IK increased eccentric peak torque significantly more than DCER (respectively, +84.2 N/m, CI95% 66.3–102.1 and +38.2 N/m, CI95% 21.9–54.4). Both IK and DCER similarly increased fascicle length (respectively, +14.7 mm, CI95% 5.4–24.0 and +14.4 mm, CI95% 5.4–23.3) and muscle thickness (respectively, +3.3 mm, CI95% 1.5–5.1, and +4.1 mm, CI95% 2.5–5.7). Matching the training volume resulted in similar adaptations comparing eccentric-only IK or DCER resistance training. Both in rehabilitation and in training practice, the use of easily available gym devices can be a good substitute for expensive and often unavailable IK devices.

Force Depression and Electromyography of Knee Extensors

Force depression (FD) of a muscle is a well-documented phenomenon showing a reduction of isometric force output after an active shortening. This has been investigated mostly with external stimulation, and few studies have employed voluntary exertion. In those studies the electromyography (EMG) has been the method mostly employed to access FD but in small muscles, and they have not focused the analysis of the EMG in frequency domain. PURPOSE: This study investigated FD after isokinetic (ISK) and submaximal isotonic (IST) exertions through surface EMG signal of knee extensors during isometric actions. METHODS: 23 health subjects (12 males and 11 females) with age 24 (±2.4) years old participated in this study after a written consent. The experimental protocol was approved by ethical committee for human research. The EMG of vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM) were registered by a DataLINK (Biometrics) during isometric tests as following. All subjects first exerted a maximal isometric test (REF), with the knee at 120o of flexion in a BIODEX machine. Further, the ISK (ω=30o/s) and IST exertions were randomly performed in the BIODEX, once by each subject, and followed by a 5s isometric action. The IST had the load set at 60% of the value obtained in REF. The isometric test that followed the ISK was maximal and the IST was 60% of the maximal. An isometric reference at 60% with the knee at 120o of flexion was also monitored. During concentric actions the knee moved from 80o to 120o. The RMS-EMG and the median frequency (MF) of the isometric tests were compared trough repeated measures ANOVA. RESULTS: Significantly lower (p=0.007) isometric torque was found after ISK (105±12 Nm) exertion than during REF (120±16Nm). A lower MF after ISK than REF was found in VL (p=0.0005) and VM (p=0.028). The RMS-EMG was higher after IST than in its isometric reference in VL (p=0.015), RF (p=0.006), and VM (p=0.002). CONCLUSION: FD after maximal concentric exertion was observed in the knee extensors due to the torque decrease. The increase in EMG activity after IST exertion may be also accounted to the FD. As FD is not a fatigue related phenomenon, the decreasing in MF is not well explainable, but if a change in pennation angle does occur due to FD, the orientation of the electrodes in relation to the fibers might have an influence on such reduction.