Cardiorespiratory, hormonal and haematological responses to submaximal cycling performed 2 days after eccentric or concentric exercise bouts

The repeated bout effect of traditional resistance training on cycling efficiency and performance

PURPOSE

This study examined the repeated bout effect of two resistance training bouts on cycling efficiency and performance.

METHODS

Ten male resistance-untrained cyclists (age 38 ± 13 years; height 180.4 ± 7.0 cm; weight 80.1 ± 10.1; kg; VO2max 51.0 ± 7.6 ml.kg-1.min-1) undertook two resistance training bouts at six-repetition maximum. Blood creatine kinase (CK), delayed-onset of muscle soreness (DOMS), counter-movement jump (CMJ), squat jump (SJ), submaximal cycling and time-trial performance were examined prior to (Tbase), 24 (T24) and 48 (T48) h post each resistance training bout.

RESULTS

There were significantly lower values for DOMS (p = 0.027) after Bout 2 than Bout 1. No differences were found between bouts for CK, CMJ, SJ and submaximal cycling performance. However, jump height (CMJ and SJ) submaximal cycling measures (ventilation and perceived exertion) were impaired at T24 and T48 compared to Tbase (p < 0.05). Net efficiency during submaximal cycling improved at Bout 2 (23.8 ± 1.2) than Bout 1 (24.3 ± 1.0%). There were no changes in cycling time-trial performance, although segmental differences in cadence were observed between bouts and time (i.e. Tbase vs T24 vs T48; p < 0.05).

CONCLUSION

Cyclists improved their cycling efficiency from Bout 1 to Bout 2 possibly due to the repeated bout effect. However, cyclists maintained their cycling completion times during exercise-induced muscle damage (EIMD) in both resistance training bouts, possibly by altering their cycling strategies. Thus, cyclists should consider EIMD symptomatology after resistance training bouts, particularly for cycling-specific technical sessions, regardless of the repeated bout effect.

The Impact of Exercise-Induced Muscle Damage on Various Cycling Performance Metrics: A Systematic Review and Meta-Analysis

ABSTRACT

Devantier-Thomas, B, Deakin, GB, Crowther, F, Schumann, M, and Doma, K. The impact of exercise-induced muscle damage on various cycling performance metrics: a systematic review and meta-analysis. J Strength Cond Res 38(1): 196-212, 2024-This systematic review and meta-analysis examined the impact of exercise-induced muscle damage (EIMD) on cycling performance. The primary outcome measure was cycling performance, whereas secondary outcome measures included creatine kinase (CK), delayed-onset muscle soreness (DOMS), and muscular contractions. Data were extracted and quantified through forest plots to report on the standardized mean difference and p values. The meta-analysis showed no significant change in oxygen consumption at 24-48 hours (p > 0.05) after the muscle damage protocol, although ventilation and rating of perceived exertion significantly increased (p < 0.05) during submaximal cycling protocols. Peak power output during both sprint and incremental cycling performance was significantly reduced (p < 0.05), but time-trial and distance-trial performance showed no change (p > 0.05). Measures of CK and DOMS were significantly increased (p < 0.05), whereas muscular force was significantly reduced following the muscle-damaging protocols (p < 0.05), confirming that cycling performance was assessed during periods of EIMD. This systematic review showed that EIMD affected both maximal and submaximal cycling performance. Therefore, coaches should consider the effect of EIMD on cycling performance when implementing unaccustomed exercise into a cycling program. Careful consideration should be taken to ensure that additional training does not impair performance and endurance adaptation.

Eccentric versus Concentric - Which Is the Most Stressful Cardiovascularly and Metabolically?

The purpose of this study was to compare the fatigability resistance profile and the physiological responses of strenuous concentric (CON) versus eccentric (ECC) isokinetic exercises. At two different sessions, 12 healthy sedentary male subjects (24.3 ± 2.5 years) performed strenuous CON and ECC isokinetic exercises. The protocol consisted of three sets of 12 maximal repetitions, separated by 30-s intervals, at a velocity of 60°·s for both flexor and extensor knee muscles of the dominant leg. Metabolic (ventilation, oxygen uptake, blood lactate concentration) and cardiovascular (HR, mean arterial blood pressure) parameters were registered before, throughout, and after the isokinetic session. The isokinetic data analysis revealed a more pronounced fatigue in the hamstrings than in the quadriceps in the ECC mode (fatigue index, ratio between the third and the first sets, of 94.8% ± 11.8% vs 86.4% ± 10.8%; P < 0.05). All physiological responses studied increased gradually during the isokinetic evaluation, both in CON and ECC modes. For total work normalized by physiological responses, cardiovascular and metabolic variables were lower in the CON than in the ECC mode, a sign of a weaker efficiency in CON mode (ratio between performance and physiological cost). In conclusion, the study shows a specific fatigability resistance profile consisting of an early decrease of ECC hamstring performance compared with the quadriceps profile. In addition, we confirm that physiological consequences are important during strenuous isokinetic exercises but ECC exercise produces less stress on the cardiovascular and the metabolic systems than does CON exercise.

Using blood lactate concentration to predict muscle damage and jump performance response to maximal stretch-shortening cycle exercise

BACKGROUND

It is well known that eccentric muscle contractions induce delayed onset muscle soreness (DOMS) and exertional rhabdomyolysis (ERB), both of which are related to high blood levels of muscle damage markers after exercise. Creatine kinase (CK) is, together with some other markers (i.e. myoglobin, α-actin, skeletal troponin), widely used in determination of muscle damage. Moreover, DOMS after eccentric exercise has been shown to be associated with altered blood lactate concentration after subsequent submaximal or maximal cycling exercise. However, it is unknown whether blood lactate can predict muscle damage levels after maximal stretch-shortening cycle (SSC) exercise, as due to the differences in types of contractions between the eccentric and SSC protocol. Additionally, we determined the association between blood lactate concentration and CMJ performance after such a protocol.

METHODS

Forty-three healthy, physically active young men completed a plyometric training session consisting of maximal countermovement jumps (CMJ) to failure. The blood creatine kinase (CK), myoglobin (Mb) and aspartate aminotransferase (AST) samples were taken pre- and 48 hours post-exercise. Blood lactate concentration was determined directly post-exercise.

RESULTS

There was a significant correlation between blood lactate concentration (post) and blood CK (P=0.027), Mb (P=0.007) and AST (P=0.024) (48 hours post), which means that higher blood lactate concentration is associated with higher muscle damage values after exercise. No correlation was found between blood lactate concentration (post) and performance loss which was expressed by the decrease in maximum CMJ height 5 minutes post-exercise.

CONCLUSIONS

Blood lactate concentration could be used as a predictor of muscle damage levels after maximal SSC exercise, which supports the results found in other studies, although after eccentric exercise. However, it cannot predict acute performance loss in jump height.

Does degree of alteration in effort sense caused by eccentric exercise significantly affect initial exercise hyperpnea in humans?

Previous research has shown an exaggeration in exercise hyperpnea 2 days after eccentric exercise (ECC). Enhancement in central command has been suggested as one candidate to account for this effect given that ECC-induced neuromuscular dysfunction increases relative exercise intensity, thus resulting in reinforcement of effort sense. The purpose of this study was, therefore, to elucidate whether the degree of alteration in effort sense caused by ECC affects exercise hyperpnea. Ten subjects performed 20-s single-arm extension-flexion exercises with weight strapped to the wrist, and ventilatory response was measured before (Pre) and 2 days after ECC (D2). Relative exercise intensity at Pre was 5 % of maximal voluntary contraction (MVC) of Pre, whereas that at D2 was 9 % MVC of D2 because of decline in muscle strength. Ventilatory responses were significantly exaggerated at D2 with a significant increase in effort sense. Although effort sense was significantly reduced during exercise at D2 when wrist weight was subtracted to match relative exercise intensity at Pre (5 % MVC of D2), ventilatory responses were still significantly higher than those of Pre. After the disappearance of post-ECC muscle damage, subjects performed the same exercise with weight added (9 % MVC of Pre) so that effort was equalized to match that of D2; however, no significant increase in ventilatory response was detected. The fact that the extent of change in effort sense caused by ECC-induced neuromuscular dysfunction did not affect ventilatory response at the onset of exercise after ECC may suggest that the exaggeration of ventilatory response after ECC is caused by mechanisms other than alteration of the central command.

The Accumulative Effect of Concentric-Biased and Eccentric-Biased Exercise on Cardiorespiratory and Metabolic Responses to Subsequent Low-Intensity Exercise: A Preliminary Study

The study investigated the accumulative effect of concentric-biased and eccentric-biased exercise on cardiorespiratory, metabolic and neuromuscular responses to low-intensity exercise performed hours later. Fourteen young men cycled at low-intensity (~60 rpm at 50% maximal oxygen uptake) for 10 min before, and 12 h after: concentric-biased, single-leg cycling exercise (CON) (performed ~19:30 h) and eccentric-biased, double-leg knee extension exercise (ECC) (~06:30 h the following morning). Respiratory measures were sampled breath-by-breath, with oxidation values derived from stoichiometry equations. Knee extensor neuromuscular function was assessed before and after CON and ECC. Cardiorespiratory responses during low-intensity cycling were unchanged by accumulative CON and ECC. The RER was lower during low-intensity exercise 12 h after CON and ECC (0.88 ± 0.08), when compared to baseline (0.92 ± 0.09; p = 0.02). Fat oxidation increased from baseline (0.24 ± 0.2 g·min(-1)) to 12 h after CON and ECC (0.39 ± 0.2 g·min(-1); p = 0.01). Carbohydrate oxidation decreased from baseline (1.59 ± 0.4 g·min(-1)) to 12 h after CON and ECC (1.36 ± 0.4 g·min(-1); p = 0.03). These were accompanied by knee extensor force loss (right leg: -11.6%, p < 0.001; left leg: -10.6%, p = 0.02) and muscle soreness (right leg: 2.5 ± 0.9, p < 0.0001; left leg: 2.3 ± 1.2, p < 0.01). Subsequent concentric-biased and eccentric-biased exercise led to increased fat oxidation and decreased carbohydrate oxidation, without impairing cardiorespiration, during low-intensity cycling. An accumulation of fatiguing and damaging exercise increases fat utilisation during low intensity exercise performed as little as 12 h later.

Time-course of recovery of peak oxygen uptake after exercise-induced muscle damage

V̇O2 peak has been shown to be reduced 48 h following exercise-induced muscle damage (EIMD), but it is unclear how long this reduction may persist. In this study eight endurance trained participants (21.5 ± 1.1 years old) performed a maximal exercise tests over 10-days followings EIMD. Cardiorespiratory variables were collected via open-circuit spirometry and soreness, maximal strength (MVC), motor-unit recruitment, and contractile properties were assessed prior to each test. MVC was reduced for up to 4-days (p ≤ 0.05) and soreness was evident for 10-days in the quadriceps (p < 0.05). V̇O2peak was reduced 7.4% 2-days post EIMD (55.5 ± 6.0 vs. 51.3 ± 5.8; p = 0.006) and remained reduced in 6 of 8 participants at 10-days post (p = 0.005). No relationship was found between changes in MVC, soreness, motor-unit recruitment, and contractile properties and changes in V̇O2peak (p > 0.05). EIMD resulted in small, but prolonged reductions in V̇O2peak. Our findings suggest mechanisms aside from force loss and soreness are primarily responsible for the reductions in V̇O2peak after EIMD.

Preventive effects of 10-day supplementation with saffron and indomethacin on the delayed-onset muscle soreness

OBJECTIVE

Delayed-onset muscle soreness (DOMS) often occurs after unaccustomed eccentric exercise and reduces exercise performance. We aimed to study the preventive effects of saffron and indomethacin on the biochemical and functional indicators of DOMS after 1-session eccentric exercise.

DESIGN

A 10-day, randomized, double-blind, placebo-controlled, pretest-posttest design.

SETTING

Controlled research laboratory.

PARTICIPANTS

Thirty-nine nonactive male university students randomly divided into saffron (n = 12), indomethacin (n = 12), and control (n = 15) groups.

INTERVENTIONS

Saffron group received 1 capsule containing dried saffron powder (n = 12, 300 mg/d), indomethacin group received 75 mg indomethacin (n = 12, 25 mg thrice a day), and control group (n = 15) received placebo capsules, 1 week before and 3 days after eccentric exercise. Ten days before and 24, 48, and 72 hours after muscle soreness protocol, the maximum isometric and isotonic forces, plasma creatine kinase (CK), plasma lactate dehydrogenase (LDH), perceived pain, knee range of movement, and thigh circumference were measured. Muscle soreness protocol was performed with a weight load equal to 80% of the maximum isotonic force in 4 sessions with 20 repetitions and 3-minute rest in between.

MAIN OUTCOME MEASURES

This study shows that 10-day supplementation with 300 mg saffron significantly decreased the CK and LDH concentrations (P < 0.0001). In the saffron group, there was no decline in maximum isometric and isotonic forces after eccentric exercise, but a significant decline in the isometric force was observed in the control group (P < 0.0001). No pain was reported in the saffron group, whereas the indomethacin group experienced pain before 72 hours (P < 0.001).

CONCLUSIONS

Results obtained from the current novel research indicate a strong preventive effect of 10-day supplementation with saffron on the DOMS.

CLINICAL RELEVANCE

The saffron can be used to prevent DOMS and alleviate the DOMS symptoms.

Monitoring neuromuscular fatigue in team-sport athletes using a cycle-ergometer test

PURPOSE

To compare a novel sprint test on a cycle ergometer with a countermovement-jump (CMJ) test for monitoring neuromuscular fatigue after Australian rules football match play.

METHODS

Twelve elite under-18 Australian rules football players (mean ± SD age 17.5 ± 0.6 y, stature 184.7 ± 8.8 cm, body mass 75.3 ± 7.8 kg) from an Australian Football League club's Academy program performed a short sprint test on a cycle ergometer along with a single CMJ test 1 h prematch and 1, 24, and 48 h postmatch. The cycle-ergometer sprint test involved a standardized warm-up, a maximal 6-s sprint, a 1-min active recovery, and a 2nd maximal 6-s sprint, with the highest power output of the 2 sprints recorded as peak power (PP).

RESULTS

There were small to moderate differences between postmatch changes in cycle-ergometer PP and CMJ PP at 1 (ES = 0.49), 24 (ES = -0.85), and 48 h postmatch (ES = 0.44). There was a substantial reduction in cycle-ergometer PP at 24 h postmatch (ES = -0.40) compared with 1 h prematch.

CONCLUSIONS

The cycle-ergometer sprint test described in this study offers a novel method of neuromuscular-fatigue monitoring in team-sport athletes and specifically quantifies the concentric component of the fatigue-induced decrement of force production in muscle, which may be overlooked by a CMJ test.

Effects of downhill and uphill exercises of equivalent submaximal intensities on selected blood cytokine levels and blood creatine kinase activity

The study was aimed at comparing the effects of concentric (CONC) and eccentric (ECC) exercises of equivalent (in terms of relative work load expressed as a percentage of VO2max) moderate intensity on selected blood cytokine levels and blood creatine kinase (CK) activity. Twenty recreationally active healthy young male volunteers were randomized between two groups that performed a single 1 h bout of CONC (uphill running) or ECC (downhill running) exercise at 60% of the respective individual VO2max. Venous blood taken 1 h before, at the end, and 24 h after the exercise was processed for plasma and analyzed for CK activity and IL-6, IL-1β and TNFα levels. There was no between-group difference in these cytokines prior to or just after the exercise, and in pre-exercise CK activity. The cytokines elevated significantly and similarly in both groups during the exercise, with no significant change in CK activity. Twenty-four hours later, CK activity and IL-6 were at pre-exercise levels in the CONC group, but showed further major increases in the ECC group, resulting in marked between-group differences in these indices. Changes in IL-1β and TNFα levels during the recovery period showed only minor differences between the study groups and produced no significant between-group difference in these cytokines. However, IL-1β level normalized in the ECC but not in the CONC group. The study suggests that moderate intensity ECC exercise compared to CONC exercise of equivalent relative work load results in considerably greater muscle damage and its related elevation in circulating IL-6, but it does not cause a major systemic inflammatory response.

The effect of prior eccentric exercise on heavy-intensity cycling: the role of gender and oral contraceptives

PURPOSE

To determine if gender and/or the use of oral contraceptives alter cycling performance with exercise-induced muscle damage (EiMD).

METHODS

Nine male adults (MEN), nine normally menstruating female adults (WomenNM), and nine female adults using oral contraceptives (WomenOC) participated. Gas exchange and time to exhaustion were measured during continuous cycling performed at three distinct power outputs before (pre) and 48 h after (post) 240 maximal effort eccentric contractions of the quadriceps muscles designed to induce muscle damage (i.e., EiMD).

RESULTS

The change in muscle damage (i.e., range of motion about the knee joint and serum creatine kinase activity) from pre- compared to post-EiMD was greater in MEN and WomenOC compared to the WomenNM. Time to exhaustion decreased after EiMD in MEN (5.19 ± 4.58 min, p = 0.01) and in WomenOC (2.86 ± 2.83 min, p = 0.02) but did not change in WomenNM (0.98 ± 2.28 min, p = 0.43). Accordingly, the slow component of O2 uptake, expressed relative to time to exhaustion (i.e., % min(-1)), was greater in post- compared to pre-EiMD for MEN (p = 0.02) and the WomenOC (p = 0.03), but not for the WomenNM (p = 0.12).

CONCLUSION

The preservation of exercise tolerance during heavy-intensity cycling performed after intense eccentric exercise is improved in women compared to men. Furthermore, the preservation of exercise tolerance is exclusive to 17β-estradiol and cannot be replicated with an exogenous synthetic estrogen replacement delivered in an oral contraceptive.

Prior eccentric exercise augments muscle pain and perception of effort during cycling exercise

OBJECTIVES

This study examined the effects of exercise-induced muscle damage (EIMD) on the physiological and perceptual responses to 30 minutes of submaximal cycling at 60% of oxygen consumption (VO2 peak).

METHODS

Ten participants completed two 30-minute bouts of cycling, one before and one 48 hours after performance of strenuous (24 contractions with 120% of concentric 1-repeition maximum) eccentric exercise.

RESULTS

Eccentric exercise resulted in a significant delayed-onset muscle pain (1.6±1.6 mm to 44.8±20 mm on a 100-mm visual analog scale; P<0.001) and a 15% (P<0.001) reduction in maximal strength 48 hours after exercise. Ratings of quadriceps muscle pain (1.99±0.42 vs. 3.30±0.56; P=0.003) and perceived exertion (RPE; 13.0±0.30 vs. 13.8±0.61; P=0.02) were elevated during cycling after EIMD at identical work rates. No changes were observed in VO2 (29.6±4.6 vs. 30.2±4.4 mL/kg/min; P=0.41), heart rate (154±15 vs. 155±9 beats/min; P=0.58), and ventilation (57.2±12.1 vs. 59.8±12.7 L/min; P=0.13) during exercise after EIMD. The mean change in RPE was significantly correlated (r=0.56; P<0.01) with the change in muscle pain during cycling and delayed-onset pain during resistance exercise (r=0.86; P<0.01), but did not correlate with changes in VO2, heart rate, ventilation, and maximal strength.

DISCUSSION

These findings indicate the elevations in RPE after EIMD are likely a consequence of the EIMD with the most likely explanation being an increase in localized pain before and during cycling exercise.

A new overtraining protocol for mice based on downhill running sessions

1. The purpose of the present study was to verify whether a downhill running protocol was able to induce non-functional overreaching in > 75% of mice. 2. Mice were divided into control (C), trained (TR) and overtrained (OTR) groups. Bodyweight and food intake were recorded weekly. The incremental load test (ILT) and the exhaustive test (ET) were used to measure performance before and after aerobic training and overtraining protocols. 3. Although the bodyweight of the OTR group was lower than that of the C group at the end of Week 7, the food intake of the OTR group was higher than that of the C and TR groups at the end of Week 8. Evaluation of results from the ILT and ET revealed significant intra- and inter-group differences: whereas the parameters measured by both tests increased significantly in the TR group, they were significantly decreased in the OTR group. 4. In conclusion, this new overtraining protocol based on downhill running sessions induced non-functional overreaching in 100% of mice.

Effects of repeated bouts of squatting exercise on sub-maximal endurance running performance

It is well established that exercise-induced muscle damage (EIMD) has a detrimental effect on endurance exercise performed in the days that follow. However, it is unknown whether such effects remain after a repeated bout of EIMD. Therefore, the purpose of this study was to examine the effects of repeated bouts of muscle-damaging exercise on sub-maximal running exercise. Nine male participants completed baseline measurements associated with a sub-maximal running bout at lactate turn point. These measurements were repeated 24-48 h after EIMD, comprising 100 squats (10 sets of 10 at 80 % body mass). Two weeks later, when symptoms from the first bout of EIMD had dissipated, all procedures performed at baseline were repeated. Results revealed significant increases in muscle soreness and creatine kinase activity and decreases in peak knee extensor torque and vertical jump performance at 24-48 h after the initial bout of EIMD. However, after the repeated bout, symptoms of EIMD were reduced from baseline at 24-48 h. Significant increases in oxygen uptake (.VO2), minute ventilation (.VE), blood lactate ([BLa]), rating of perceived exertion (RPE), stride frequency and decreases in stride length were observed during sub-maximal running at 24-48 h following the initial bout of EIMD. However, following the repeated bout of EIMD, .VO2, .VE, [BLa], RPE and stride pattern responses during sub-maximal running remained unchanged from baseline at all time points. These findings confirm that a single resistance session protects skeletal muscle against the detrimental effects of EIMD on sub-maximal running endurance exercise.

Muscle damage alters the metabolic response to dynamic exercise in humans: a31P-MRS study

We used31P-magnetic resonance spectroscopy to test the hypothesis that exercise-induced muscle damage (EIMD) alters the muscle metabolic response to dynamic exercise, and that this contributes to the observed reduction in exercise tolerance following EIMD in humans. Ten healthy, physically active men performed incremental knee extensor exercise inside the bore of a whole body 1.5-T superconducting magnet before (pre) and 48 h after (post) performing 100 squats with a load corresponding to 70% of body mass. There were significant changes in all markers of muscle damage [perceived muscle soreness, creatine kinase activity (434% increase at 24 h), and isokinetic peak torque (16% decrease at 24 h)] following eccentric exercise. Muscle phosphocreatine concentration ([PCr]) and pH values during incremental exercise were not different pre- and post-EIMD ( P > 0.05). However, resting inorganic phosphate concentration ([Pi]; pre: 4.7 ± 0.8; post: 6.7 ± 1.7 mM; P < 0.01) and, consequently, [Pi]/[PCr] values (pre: 0.12 ± 0.02; post: 0.18 ± 0.05; P < 0.01) were significantly elevated following EIMD. These mean differences were maintained during incremental exercise ( P < 0.05). Time to exhaustion was significantly reduced following EIMD (519 ± 56 and 459 ± 63 s, pre- and post-EIMD, respectively, P < 0.001). End-exercise pH (pre: 6.75 ± 0.04; post: 6.83 ± 0.04; P < 0.05) and [PCr] (pre: 7.2 ± 1.7; post: 14.5 ± 2.1 mM; P < 0.01) were higher, but end-exercise [Pi] was not significantly different (pre: 19.7 ± 1.9; post: 21.1 ± 2.6 mM, P > 0.05) following EIMD. The results indicate that alterations in phosphate metabolism, specifically the elevated [Pi] at rest and throughout exercise, may contribute to the reduced exercise tolerance observed following EIMD.

Metabolic consequences of exercise-induced muscle damage

Exercise-induced muscle damage (EIMD) is commonly experienced following either a bout of unaccustomed physical activity or following physical activity of greater than normal duration or intensity. The mechanistic factor responsible for the initiation of EIMD is not known; however, it is hypothesised to be either mechanical or metabolic in nature. The mechanical stress hypothesis states that EIMD is the result of physical stress upon the muscle fibre. In contrast, the metabolic stress model predicts that EIMD is the result of metabolic deficiencies, possibly through the decreased action of Ca(2+)-adenosine triphosphatase. Irrespective of the cause of the damage, EIMD has a number of profound metabolic effects. The most notable metabolic effects of EIMD are decreased insulin sensitivity, prolonged glycogen depletion and an increase in metabolic rate both at rest and during exercise. Based on current knowledge regarding the effects that various types of damaging exercise have on muscle metabolism, a new model for the initiation of EIMD is proposed. This model states that damage initiation may be either metabolic or mechanical, or a combination of both, depending on the mode, intensity and duration of exercise and the training status of the individual.

Effects of a 30-min running performed daily after downhill running on recovery of muscle function and running economy

This study investigated the effects of a 30-min level running performed daily for 6 days after downhill running (DHR) on indicators of muscle damage and running economy (RE). Fifty men were placed into five groups - control (CON), 40%, 50%, 60% and 70% (10 subjects per group) - by matching the baseline maximal oxygen consumption (V O(2max)) among the groups. Subjects in the 40%, 50%, 60% and 70% groups had a treadmill (0 degrees ) run for 30min at 40%, 50%, 60% and 70% of the pre-determined V O(2max), respectively, at 1-6 days after a bout of 30-min DHR at -15% (-8.5 degrees ). Maximal voluntary isometric strength of the knee extensors, muscle soreness, plasma creatine kinase and lactate dehydrogenase activities were measured before, immediately after and every day for 7 days after DHR. RE was assessed by oxygen consumption, minute ventilation, respiratory exchange ratio, lactate, heart rate and rating of perceived exertion during a 5-min level running at 85% V O(2max) performed before and at 2, 5 and 7 days after DHR. All muscle damage markers changed significantly (P<0.05) after DHR without significant differences among the groups. The RE parameters showed a significant decrease in RE for 7 days after DHR, but no significant differences in the changes were evident among the groups. These results suggest that the daily running performed after DHR did not have any beneficial or adverse effects on recovery of muscle damage and RE regardless of the intensity.

Ventilatory and circulatory responses at the onset of exercise after eccentric exercise

The purpose of this study was to clarify whether delayed onset muscle soreness (DOMS) and muscle damage after eccentric exercise (ECC) could affect the ventilatory and circulatory responses at the onset of exercise, and whether those effects would continue after the disappearance of DOMS. Ten males participated in this study. We measured ventilatory and circulatory responses at the onset of exercise, for the first 20 s, during knee extension-relaxation voluntary exercise (VOL) and passive movement (PAS), which was achieved by the experimenter alternatively pulling ropes connected to the subjects' ankles for the same period and frequency as during VOL. VOL and PAS were performed before, 2 days after, and 7 days after ECC. The following results were found: (1) the gain of minute ventilation at the onset of VOL at 2 days after ECC was significantly larger than that of before ECC; (2) the gain of minute ventilation at 7 days after ECC during both VOL and PAS was also enhanced significantly as compared to that of before ECC; and (3) heart rate and blood pressure responses were unchanged throughout the experimental period. In conclusion, ventilatory response at the onset of exercise is augmented during DOMS and EIMD after ECC and the enhanced ventilatory response continued after the disappearance of DOMS. It is suggested that enhanced ventilatory response during exercise after ECC is attributed to at least the changes in neural factors and that the mechanisms inducing these augmented ventilatory responses should be different during the period after ECC.

Effects of eccentric exercise on cycling efficiency

The aim of this study was to find out whether the efficiency of concentric muscle contraction is impaired by eccentric squatting exercise. The study involved 25 male physical education students in two experiments. In the first experiment 14 subjects undertook cycling exercise at 65% VO(2)max until exhaustion on two occasions. During the experimental condition their cycling was interrupted every 10 min so they could perform eccentric squatting exercise, whereas in the control condition they rested seated on the bike during the interruptions. Eccentric squatting consisted of 10 series of 25 reps with a load equivalent to 150% of the subject's body mass on the shoulders. During the first experiment gross efficiency decreased (mean +/- SE) from 17.1 +/- 0.3 to 16.0 +/- 0.4%, and from 17.2 +/- 0.3 to 16.5 +/- 0.4%, between the 2nd and 9th cycling bouts of the experimental and control conditions, respectively (both p < 0.05). The reduction in cycling efficiency was similar in both conditions (p = 0.10). Blood lactate concentration [La] was higher during the experimental than in the control condition (p < 0.05), but substrate oxidation was similar. MVC was decreased similarly (25-28%) in both conditions. The 11 subjects participating in the second experiment undertook 25 reps of eccentric squatting exercise only, each with a load equivalent to 95% of his maximal voluntary contraction (MVC), repeated every 3 min until exhaustion. One hour after the end of the eccentric squatting exercise series cycling, VO(2) and gross cycling efficiency were comparable to the values observed before the eccentric exercise. Both experimental protocols with eccentric exercise elicited similar muscle soreness 2 days later; however, at this time cycling efficiency was similar to that observed prior to eccentric exercise. The interposition of cycling exercise between the eccentric exercise bouts accelerated the recovery of MVC. We conclude that eccentric exercise does not alter or has only a marginal effect on gross cycling efficiency even in presence of marked muscle soreness.

Recovery of running performance following muscle-damaging exercise: relationship to brain IL-1beta

Recovery following muscle-damaging downhill running is associated with increased muscle inflammatory cytokines. Various inflammatory challenges can also increase cytokines in the brain, which have been linked to sickness behaviors, including fatigue, but little is known about the brain cytokine response to stressful exercise. We used a downhill running model to determine the relationship between brain IL-1beta and recovery of running performance. Male C57BL/6 mice were assigned to: downhill (DH), uphill (UH), or non-running control (Con) groups and run on a treadmill at 22 m/min and -14% or 14% grade, for 150 min. Following the run, a subset of DH and UH was placed into activity wheel cages where voluntary running activity was measured for 7 days. A second subset was run to fatigue on a motorized treadmill at 36 m/min, 8% grade at 24, 48, and 96 h post-up/downhill run. A third subset of DH, UH, and Con mice had brains dissected and assayed for IL-1beta at 24 and 48 h. DH resulted in delayed recovery of both voluntary wheel-running and treadmill running to fatigue as compared to UH (p < .05). DH was also associated with increased IL-1beta concentrations in cortex (at 24 and 48 h) and cerebellum (24 h) as compared to UH and Con. UH was not different than Con in any brain region. Eccentric-biased downhill running results in an increase in plasma CK and delayed recovery in running performance, as compared to the more metabolically demanding uphill running, and this was associated with increased concentrations of IL-1beta in regions of the brain responsible for movement, coordination, motivation, perception of effort, and pain.

Short-term effects of repetitive arm work and dynamic exercise on glucose metabolism and insulin sensitivity

AIM

To determine whether repetitive arm work, with a large component of static muscle contraction alters glucose metabolism and insulin sensitivity.

METHOD

Euglycemic clamps (2 h) were started in ten healthy individuals 15 min after 37 min periods of: (1) repetitive arm work in a simulated occupational setting; (2) dynamic concentric exercise on a cycle ergometer at 60% of VO(2max) and (3) a resting regime as a control. During the experimental periods, blood samples were collected, blood pressure was measured repeatedly and electrocardiogram (ECG) was recorded continuously. During the clamps, euglycemia was maintained at 5 mmol l(-1) and insulin was infused at 56 mU m(-2) min(-1) for 120 min.

RESULTS

The insulin-mediated glucose disposal rate (M-value) for the steady-state period (60-120 min) of the clamp, tended to be lower following arm work than for both cycling and resting regimes. When dividing the steady-state period into 20-min intervals, the insulin sensitivity index (ISI) was significantly lower for arm work compared with the resting control situation between 60-80 min (P = 0.04) and 80-100 min (P = 0.01), respectively. Catecholamines increased significantly for arm work and cycling compared with resting regime. Data from heart rate variability (HRV) measurements indicated significant sympathetic activation during repetitive arm work.

CONCLUSION

The results indicate that repetitive arm work might acutely promote insulin resistance, whereas no such effect on insulin resistance was produced by dynamic concentric exercise.

The Mechanisms of Massage and Effects on Performance, Muscle Recovery and Injury Prevention

Many coaches, athletes and sports medicine personnel hold the belief, based on observations and experiences, that massage can provide several benefits to the body such as increased blood flow, reduced muscle tension and neurological excitability, and an increased sense of well-being. Massage can produce mechanical pressure, which is expected to increase muscle compliance resulting in increased range of joint motion, decreased passive stiffness and decreased active stiffness (biomechanical mechanisms). Mechanical pressure might help to increase blood flow by increasing the arteriolar pressure, as well as increasing muscle temperature from rubbing. Depending on the massage technique, mechanical pressure on the muscle is expected to increase or decrease neural excitability as measured by the Hoffman reflex (neurological mechanisms). Changes in parasympathetic activity (as measured by heart rate, blood pressure and heart rate variability) and hormonal levels (as measured by cortisol levels) following massage result in a relaxation response (physiological mechanisms). A reduction in anxiety and an improvement in mood state also cause relaxation (psychological mechanisms) after massage. Therefore, these benefits of massage are expected to help athletes by enhancing performance and reducing injury risk. However, limited research has investigated the effects of pre-exercise massage on performance and injury prevention. Massage between events is widely investigated because it is believed that massage might help to enhance recovery and prepare athletes for the next event. Unfortunately, very little scientific data has supported this claim. The majority of research on psychological effects of massage has concluded that massage produces positive effects on recovery (psychological mechanisms). Post-exercise massage has been shown to reduce the severity of muscle soreness but massage has no effects on muscle functional loss. Notwithstanding the belief that massage has benefits for athletes, the effects of different types of massage (e.g. petrissage, effleurage, friction) or the appropriate timing of massage (pre-exercise vs post-exercise) on performance, recovery from injury, or as an injury prevention method are not clear. Explanations are lacking, as the mechanisms of each massage technique have not been widely investigated. Therefore, this article discusses the possible mechanisms of massage and provides a discussion of the limited evidence of massage on performance, recovery and muscle injury prevention. The limitations of previous research are described and further research is recommended.

Metabolic response to prolonged cycling with (13)C-glucose ingestion following downhill running

The purpose of this study was to describe the effect of muscle damage and delayed-onset muscle soreness (DOMS) on the metabolic response during a subsequent period of prolonged concentric exercise (120 min, approximately 61% V(.)O(2max), on a cycle ergometer), with ingestion of 3 g of (13)C-glucose/kg body mass. We hypothesized that the oxidation of plasma and exogenous glucose would be reduced, while the oxidation of glucose arising from muscle glycogen would be increased. Six male subjects were studied during exercise in a control situation and 2 days following downhill running, at a time when plasma creatine kinase (CK) activity was increased, and DOMS was present. Carbohydrate and lipid oxidation were computed from indirect respiratory calorimetry corrected for protein oxidation, while the oxidation of plasma glucose and muscle glycogen were computed from V(.)(13)CO(2) and the ratio of (13)C/(12)C in the plasma glucose. All data were presented as the mean and the standard error of the mean. The oxidation of protein (approximately 6% energy yield, in the control and the experimental trial), lipid (approximately 15 and approximately 18%), and carbohydrate (approximately 79 and approximately 76%), as well as that of plasma glucose (approximately 41 and approximately 46%), glucose from the liver (approximately 12 and approximately 14%), and glucose from muscle glycogen (approximately 38 and approximately 31%) were not significantly different between the control and experimental (DOMS) trials. The response of the plasma glucose, insulin, lactate, and free fatty acid concentrations was not modified by the previous eccentric exercise. These results indicate that the metabolic response to prolonged concentric exercise is not modified by muscle damage and DOMS resulting from a bout of eccentric exercise performed 2 days before.

Neuromuscular function after exercise-induced muscle damage: theoretical and applied implications

Exercise-induced muscle damage is a well documented phenomenon particularly resulting from eccentric exercise. When eccentric exercise is unaccustomed or is performed with an increased intensity or duration, the symptoms associated with muscle damage are a common outcome and are particularly associated with participation in athletic activity. Muscle damage results in an immediate and prolonged reduction in muscle function, most notably a reduction in force-generating capacity, which has been quantified in human studies through isometric and dynamic isokinetic testing modalities. Investigations of the torque-angular velocity relationship have failed to reveal a consistent pattern of change, with inconsistent reports of functional change being dependent on the muscle action and/or angular velocity of movement. The consequences of damage on dynamic, multi-joint, sport-specific movements would appear more pertinent with regard to athletic performance, but this aspect of muscle function has been studied less often. Reductions in the ability to generate power output during single-joint movements as well as during cycling and vertical jump movements have been documented. In addition, muscle damage has been observed to increase the physiological demand of endurance exercise and to increase thermal strain during exercise in the heat. The aims of this review are to summarise the functional decrements associated with exercise-induced muscle damage, relate these decrements to theoretical views regarding underlying mechanisms (i.e. sarcomere disruption, impaired excitation-contraction coupling, preferential fibre type damage, and impaired muscle metabolism), and finally to discuss the potential impact of muscle damage on athletic performance.

Acute impact of submaximal resistance exercise on immunological and hormonal parameters in young men

In this study, we examined the acute effects of submaximal resistance exercise on immunological and hormonal parameters in 7 resistance-trained and 10 non-resistance-trained males. The participants, who were aged 29.5 +/- 7.1 years (mean +/- s), performed submaximal resistance exercise at 75% of their one-repetition maximum. Blood samples were taken before, during, immediately after, and 30, 60 and 120 min after exercise and analysed for leukocyte subpopulations and stress hormones. Total leukocytes, neutrophils and monocytes increased during exercise, reaching their maximum 2 h after exercise. Lymphocytes increased during exercise, T-helper cells returned to resting values after exercise, and natural killer cells and T-suppressor cells decreased below resting values. The CD4/CD8 ratio decreased during exercise but increased during recovery. The resistance-trained participants tended to have lower T-helper cell counts before, during and immediately after exercise and a lower CD4/CD8 ratio during recovery than the non-resistance-trained participants. Plasma cortisol correlated positively with leukocytes during exercise (r = 0.572, P < 0.05), but negatively with T-helper cells 30 and 60 min after exercise (r = -0.573, P < 0.05; r = -0.642, P < 0.01, respectively). Our results indicate that resistance exercise leads to acute changes in leukocyte counts, despite moderate hormonal changes, independent of training status. Regular resistance exercise might lead to decreased T-helper cell counts and a lower CD4/CD8 ratio, which could increase susceptibility to infections.

Tourniquet obliteration of exercise-induced sensory nerve conduction augmentation

OBJECTIVE

We previously discovered that minimally suprathreshold sensory nerve action potential amplitudes increased during isometric muscle contraction. In this study, the hypothesis was that the exercise-induced response could be blocked with a tourniquet.

METHODS

A total of 21 healthy male and female subjects were recruited from the medical center. Baseline and postevent serial sural nerve recordings were made in the leg of 16 healthy subjects under the following conditions: (1) blood pressure cuff inflation at the arm, (2) isometric muscle contraction in the hand, and (3) conditions 1 and 2 combined.

RESULTS

Results showed there was a 2.9 microV increase in the sural nerve response 5 min after muscle contraction compared to baseline at rest. The exercise-induced sensory response was largely obliterated by the blood pressure cuff with exception of the 1-min postexercise recording.

CONCLUSION

In conclusion, the results show a tourniquet placed on the proximal arm blocks the effect of the muscle contraction of the hand on the minimally suprathreshold sensory sural nerve conduction recording in the ankle. The likely reason for this is the interruption of a thus far unidentified circulating factor. The clinical implication is the discovery of a sensory regulatory mechanism controlled by the motor system.

Delayed-Onset Muscle Soreness Does Not Alter the Kinematics and Kinetics of the Squat-Lifting Technique

Context:

Little research has been done evaluating the effects of muscle soreness on a lifting task.

Objective:

To examine the effects of delayed-onset muscle soreness (DOMS) in the thigh musculature on kinematic and kinetic variables associated with the squat-lifting technique.

Design:

Pretest–posttest repeated measures, with treatment as the independent variable (DOMS and no DOMS of the thigh musculature).

Setting:

Research laboratory.

Participants:

Twenty healthy college students.

Intervention:

Subjects were videotaped lifting a 157-N crate before and after DOMS inducement.

Main Outcome Measures:

A 2-dimensional sagittal-plane video analysis was used to calculate 7 kinematic and kinetic variables.

Results:

DOMS had no effect on L5/S1 torque and shear or compression, hip torque and range of motion, or knee torque and range of motion during lifting.

Conclusions:

DOMS does not appear to alter kinematic and kinetic variables associated with the squat-lifting technique.

Effect of eccentric exercise on muscle oxidative metabolism in humans

PURPOSE

The purpose of this study was to evaluate the effects of eccentric exercise on muscle oxidative function.

METHODS

Thirteen subjects performed high-intensity eccentric cycling for 30 min. Muscle oxidative function in vastus lateralis was evaluated by measurements of respiration in permeabilized muscle fibers (skinned fibers) and from the kinetics of oxyhemoglobin (oxyHb) saturation measured with near infrared spectroscopy (NIRS).

RESULTS

After eccentric cycling, all subjects reported extensive delayed onset muscle soreness (DOMS), but plasma markers of muscle damage (creatine kinase and beta-glucuronidase activity) were not significantly altered. The half time of oxyHb desaturation after circulatory occlusion (128 +/- 11 s, mean +/- SE) and oxyHb resaturation after restoration of blood flow (13.8 +/- 0.7 s) were not significantly changed after eccentric cycling (N = 7). Respiration in skinned muscle fibers measured in the absence of ADP and in the presence of a submaximal (0.1 mM) or maximal ADP concentration (1 mM) was not significantly changed after eccentric cycling (N = 6). The sensitivity of respiration to ADP was not significantly changed after eccentric cycling.

CONCLUSIONS

Muscle oxidative function (maximal respiration and respiratory control by ADP) was not compromised after high-intensity eccentric cycle exercise. Furthermore, NIRS indicates that after eccentric cycling muscle oxygen utilization and local oxygen transport at rest are unchanged. It is concluded that eccentric cycling, although causing DOMS, does not negatively affect skeletal muscle oxidative function.

Increased threshold sural amplitude after upper limb isometric contraction in complete paraplegics

OBJECTIVE

To determine whether the enhancement of threshold sural sensory nerve action potentials (SNAPs) occurred in patients with spinal cord injury after upper limb isometric contraction.

DESIGN

This prospective study, in which ten paraplegic patients with spinal cord injury were recruited from the Harris County community and served as his/her own control, was performed in the electromyography laboratory at Harris County Hospital District Quentin Mease Hospital. The baseline SNAP was established using ten threshold, signal-averaged stimuli to the sural nerve. With the same stimulus strength, the SNAP was recorded while the subjects' arms were pulled apart against a force gauge at 50% and 100% maximum force. Responses were recorded every 4 min until the values returned to baseline.

RESULTS

Results showed an increase in the SNAP amplitude after 50% and 100% maximum force. The mean preexercise SNAP amplitude was 4.0 +/- 0.6 (SE) microV. At 50% force, the SNAP amplitude was 7.57 +/- 1.2 microV; at 100% force, it was 7.29 +/- 1.2 microV. The post hoc analysis of the data revealed P = 0.009 and P = 0.01 for 50% and 100% maximum force, respectively.

CONCLUSIONS

The threshold SNAP of the sural nerve was enhanced after isometric exercise in paraplegic patients with spinal cord injury.

Contribution of circulating acetylcholine to sensory nerve conduction augmentation

We previously discovered that sensory nerve action potential amplitudes increased during isometric muscle contraction and that this response could be blocked with tourniquet isolation of the contraction source. The hypothesis for this study was that a circulating factor was responsible for this effect. In this prospective study, baseline and post intravenous injection of serial sural nerve action potential recordings were made in the leg of 8 rabbits. The sequence of the injections was randomized: 1) normal saline placebo, 2) 0.01 mg/kg acetylcholine (ACh) 3) 200 mg/kg Na acetate, 4) 260 mg/kg Na lactate, and 5) 20 mg/kg choline. Results showed there was a 3.8 microV increase in the sural nerve response 6 min after ACh injection compared to baseline at rest (p = .01, power = .9, analysis of variance (ANOVA), repeated measures). There were no significant changes in the amplitudes of the sural nerve after injection of the remaining agents or placebo (p = .33 to .81, ANOVA, repeated measures). In conclusion, circulating ACh is the only agent tested thus far that appears to be responsible for this effect. In addition, the amplitude and temporal curve of this response is similar to that seen after exercise in human subjects. The clinical importance of this study is that ACh plays a role in this newly discovered sensory regulatory mechanism controlled by the motor system.

The role of passive muscle stiffness in symptoms of exercise-induced muscle damage

We examined whether passive stiffness of an eccentrically exercising muscle group affects the subsequent symptoms of muscle damage. Passive hamstring muscle stiffness was measured during an instrumented straight-leg-raise stretch in 20 subjects (11 men and 9 women) who were subsequently classified as "stiff" (N = 7), "normal" (N = 6), or "compliant" (N = 7). Passive stiffness was 78% higher in the stiff subjects (36.2 +/- 3.3 N.m.rad(-1)) compared with the compliant subjects (20.3 +/- 1.8 N.m.rad(-1)). Subjects then performed six sets of 10 isokinetic (2.6 rad.s(-1)) submaximal (60% maximal voluntary contraction) eccentric actions of the hamstring muscle group. Symptoms of muscle damage were documented by changes in isometric hamstring muscle strength, pain, muscle tenderness, and creatine kinase activity on the following 3 days. Strength loss, pain, muscle tenderness, and creatine kinase activity were significantly greater in the stiff compared with the compliant subjects on the days after eccentric exercise. Greater symptoms of muscle damage in subjects with stiffer hamstring muscles are consistent with the sarcomere strain theory of muscle damage. The present study provides experimental evidence of an association between flexibility and muscle injury. Muscle stiffness and its clinical correlate, static flexibility, are risk factors for more severe symptoms of muscle damage after eccentric exercise.

The effect of a prophylactic dose of flurbiprofen on muscle soreness and sprinting performance in trained subjects

The aim of this study was to examine the effects of a prophylactic dose of a local, transcutaneously administered, non-steroidal anti-inflammatory drug on muscle soreness, muscle damage and sprinting performance in young trained males. Twenty-five subjects aged 19+/-3 years, actively participating in rugby union and field hockey, were familiarized with the test procedure and then divided at random into an experimental group (n = 13) and a control group (n = 12). The experimental group received two patches, each containing 40 mg flurbiprofen (TransAct LAT), 12 h before an exercise bout designed to produce delayed-onset soreness (DOMS). The control group received identical non-medicated placebo patches at the same time. Delayed-onset muscle soreness was induced by an exercise protocol consisting of drop jumps (seven sets of 10 repetitions). Serum creatine kinase activity, muscle soreness, muscle girth and acceleration in a maximal sprint over 30 m were measured before the induction of DOMS and at 12, 24, 48 and 72 h thereafter. Plasma lactate concentration was measured 3 min after the 30-m sprint tests. Subjects in both groups had significantly more pain at 24 and 48 h compared with at 12 and 72 h (P < 0.05; Friedman two-way analysis of variance). Thigh girth and serum creatine kinase did not change throughout the experiment. Although plasma lactate concentrations were elevated after the 30-m sprint, there were no differences between groups or as a result of DOMS. The greatest acceleration occurred between 5 and 10 m. This was not affected by the anti-inflammatory drug or DOMS. In conclusion, the aetiology of the DOMS induced in the trained subjects in this study seems to be independent of inflammatory processes or, more specifically, of increases in prostaglandin synthesis in the muscles.

Exercise-induced muscle injury augments forearm vascular resistance during leg exercise

The purpose of the present investigation was to examine the effect of exercise-induced muscle injury on hemodynamic responses during exercise. Ten subjects performed unilateral isometric knee extensions (IKE) at 30% of preinjury maximum voluntary contraction to fatigue and for 3 min before and 48 h after muscle injury. Muscle injury was elicited by performing 8 sets of 10 repetitions of eccentric muscle actions of the knee extensor muscles (i.e., quadriceps muscles) by lowering a weight equivalent to 75% of eccentric maximum load. Exercise time to fatigue for IKE at 30% of maximum voluntary contraction in the injured leg was significantly decreased from preinjury to postinjury IKE (257 +/- 21 to 203 +/- 23 s; n = 10), but was unchanged in the control leg (244 +/- 16 to 254 +/- 20 s; n = 7). With the use of a 10-cm visual analog scale, ratings of muscle soreness in the injured leg increased from 0 to 5. 1 +/- 0.7 cm (P < 0.001) but were not changed in the control leg (0 both times). Both heart rate and mean arterial pressure responses to exercise were unchanged following muscle injury. Forearm blood flow and forearm vascular resistance were not different at rest and during the first minute of exercise before and after muscle injury. However, after muscle injury, forearm blood flow was significantly lower and forearm vascular resistance was significantly higher (P < 0.03) during the second and third minutes of exercise. There were no significant changes in any variables with the contralateral control leg. In four subjects, resting magnetic resonance images demonstrated a 23% greater relative cross-sectional area of the knee extensor muscles with an elevated transverse relaxation time in the injured versus control leg. The results indicate that forearm vascular resistance is augmented during isometric knee extension following muscle injury of the knee extensor muscles. The data suggest that muscle injury alters vascular control to non-exercising skeletal muscle during exercise.

A method of detecting the muscle pain threshold using an objective software-mediated technique

This paper describes the reliability of a new procedure of applying force to a muscle site using a computer-mediated myometric procedure to measure a discomfort-pain threshold. 24 female subjects were divided into four groups. Each group was tested on three occasions (trial) at four muscle sites (site) repeated daily over four days (day). Each group received one of four different rates of force application (ramp). Analysis of variance (ramp by day by site by trial) showed a significant main effect for trials and discomfort-pain threshold at different muscle sites, but no significant main effect for days or ramps. Intraclass correlations for each muscle site were in the range of R = 0.73 to 0.98. This procedure appears to be a valid, reliable and nonintrusive means of assessing the muscle discomfort-pain threshold.