Changes in running economy following downhill running

Muscle injury after low-intensity downhill running reduces running economy

Contraction-induced muscle injury may reduce running economy (RE) by altering motor unit recruitment, lowering contraction economy, and disturbing running mechanics, any of which may have a deleterious effect on endurance performance. The purpose of this study was to determine if RE is reduced 2 days after performing injurious, low-intensity exercise in 11 healthy active men (27.5 ± 5.7 years; 50.05 ± 1.67 VO2peak). Running economy was determined at treadmill speeds eliciting 65 and 75% of the individual's peak rate of oxygen uptake (VO2peak) 1 day before and 2 days after injury induction. Lower extremity muscle injury was induced with a 30-minute downhill treadmill run (6 × 5 minutes runs, 2 minutes rest, -12% grade, and 12.9 km·h(-1)) that elicited 55% VO2peak. Maximal quadriceps isometric torque was reduced immediately and 2 days after the downhill run by 18 and 10%, and a moderate degree of muscle soreness was present. Two days after the injury, steady-state VO2 and metabolic work (VO2 L·km(-1)) were significantly greater (4-6%) during the 65% VO2peak run. Additionally, postinjury VCO2, VE and rating of perceived exertion were greater at 65% but not at 75% VO2peak, whereas whole blood-lactate concentrations did not change pre-injury to postinjury at either intensity. In conclusion, low-intensity downhill running reduces RE at 65% but not 75% VO2peak. The results of this study and other studies indicate the magnitude to which RE is altered after downhill running is dependent on the severity of the injury and intensity of the RE test.

The impact of a pre-loaded multi-ingredient performance supplement on muscle soreness and performance following downhill running

The effects of multi-ingredient performance supplements (MIPS) on perceived soreness, strength, flexibility and vertical jump performance following eccentric exercise are unknown. The purpose of this study was to determine the impact of MIPS (NO-Shotgun®) pre-loaded 4 weeks prior to a single bout of downhill running (DHR) on muscle soreness and performance. Trained male runners (n = 20) were stratified by VO_2max, strength, and lean mass into two groups; MIPS (n = 10) ingested one serving daily of NO-Shotgun® for 28 days and 30 min prior to all post-testing visits, Control (CON; n = 10) consumed an isocaloric maltodextrin placebo in an identical manner as MIPS. Perceived soreness and performance measurements (strength, flexibility, and jump height) were tested on 6 occasions; 28 days prior to DHR, immediately before DHR (PRE), immediately post (POST) DHR, 24, 48, and 72 hr post-DHR. Perceived soreness significantly increased (p < 0.05) post DHR compared to PRE at all time-points, with no difference between groups. Creatine kinase (CK) and lactate dehydrogenase (LDH) increased over time (p < 0.001) with no group x time interactions (p = 0.236 and p = 0.535, respectively). Significant time effects were measured for strength (p = 0.001), flexibility (p = 0.025) and vertical jump (p < 0.001). There were no group x time interactions for any performance measurements. Consumption of MIPS for 4 weeks prior to a single bout of DHR did not affect perceived soreness, muscle damage, strength, flexibility, or jump performance compared to an isocaloric placebo in trained male runners following a single bout of DHR.

A review of nutritional intervention on delayed onset muscle soreness. Part I

This review is focused on the effect of nutritional intervention on delayed onset muscle soreness (DOMS) that occurs after exercise. In general, high force eccentric contractions and/or unaccustomed exercise result in DOMS attributed to reduction in performance such as muscle strength and range of motion (ROM) for both athletes and non-athletes. Nutritional intervention is one of the preventive or therapeutic ways to reduce DOMS. Previous research studies have suggested the following nutrition intervention: caffeine, omega-3 fatty acids, taurine, polyphenols, and so on. Nutritional intervention with these nutrients before and after exercise was reported to be effective in reducing DOMS. These nutritional interventions have also been reported to affect inflammatory responses and oxidative stress leading to DOMS reduction. However, other studies have reported that these nutritional interventions have no effect on DOMS. It is suggested that intake of proper nutrition intervention can effectively reduce DOMS after exercise and quickly help an athlete return to exercise or training program. In addition, nutritional intervention may help both athletes and non-athletes who engage in physical therapy or rehabilitative programs after surgery or any injurious events.

Prophylactic ankle taping: influence on treadmill-running kinematics and running economy

Prophylactic ankle taping (PAT) is commonly used in sport. Prophylactic ankle taping may restrict ankle motion, which would affect the kinetic chain and alter gait. The purpose of this study was to examine the effects of PAT on lower extremity (LE) kinematics and running economy during treadmill running. Twelve recreational runners (9 women, 3 men; M ± SD age = 31.33 ± 8.04 years, height = 1.67 ± 0.81 m, mass = 61.84 ± 9.38 kg) completed two 20-minute running sessions (PAT and no tape: control [CON]) at a self-selected pace. Before each run, reflective markers were placed along the right side of the body. Sagittal plane kinematic data (60 Hz) were captured 4 times, and expired gases were measured for 2-minute after each video capture during both trials. Stride frequency, stride length, LE kinematic variables at initial contact and end contact (EC) were calculated. Cardiorespiratory variables and heart rate were also measured. Running economy was normalized to oxygen uptake per unit body mass per kilometer (milliliter per kilogram per kilometer) as running speeds varied. At EC, the PAT hip angle significantly decreased (p = 0.01) by 3.82°, whereas CON decreased by 0.85°. The range of motion tended to decrease over the 20-minute run (p = 0.08). Heart rate significantly increased over time (6.7%) but was not different between conditions. Prophylactic ankle taping did not significantly affect the physiological measures associated with the metabolic cost of treadmill running or the other kinematic variables. These findings suggest that the hip angle continued to decrease during the PAT condition at push-off in recreational runners without impacting the metabolic cost of transport.

Postactivation potentiation biases maximal isometric strength assessment

Postactivation potentiation (PAP) is known to enhance force production. Maximal isometric strength assessment protocols usually consist of two or more maximal voluntary isometric contractions (MVCs). The objective of this study was to determine if PAP would influence isometric strength assessment. Healthy male volunteers (n = 23) performed two five-second MVCs separated by a 180-seconds interval. Changes in isometric peak torque (IPT), time to achieve it (tPTI), contractile impulse (CI), root mean square of the electromyographic signal during PTI (RMS), and rate of torque development (RTD), in different intervals, were measured. Significant increases in IPT (240.6 ± 55.7 N·m versus 248.9 ± 55.1 N·m), RTD (746 ± 152 N·m·s⁻¹versus 727 ± 158 N·m·s⁻¹), and RMS (59.1 ± 12.2% RMS_MAX   versus 54.8 ± 9.4% RMS_MAX) were found on the second MVC. tPTI decreased significantly on the second MVC (2373 ± 1200 ms versus 2784 ± 1226 ms). We conclude that a first MVC leads to PAP that elicits significant enhancements in strength-related variables of a second MVC performed 180 seconds later. If disconsidered, this phenomenon might bias maximal isometric strength assessment, overestimating some of these variables.

Monitoring muscle damage markers during a four-week downhill walking exercise program

Eccentric-based exercise is known to induce muscle damage (MD). The purpose of this study was to investigate effect of downhill walking (DW) sessions on MD and aerobic markers in young adults. Eight male subjects were submitted to a 4-week DW periodized exercise program. Subjects' soreness (SOR) was assessed each training day. Serum creatine quinase activity (CK) was collected before the first training session, and at the end of each of the four weeks. Oxygen uptake (VO2) and perceived exertion (PE) were assessed during the last training session every week. Increases in SOR were found only at the third and fourth training days. Increased CK concentration was found at the third training week. No significant increases in VO2 and PE were found throughout the program. We concluded that DW sessions elicit significant MD, but not enough to impair it in further sessions. Therefore, DW can be used as a training protocol following proper periodization.

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 single bout of downhill running transiently increases HOMA-IR without altering adipokine response in healthy adult women

PURPOSE

Eccentric exercise-induced muscle damage may cause marked alterations in insulin sensitivity. However, it is not entirely known whether such alterations are also related to changes in adipokine levels. The aim of this study was to investigate the effects of muscle damage due to downhill running on inflammation, insulin sensitivity and selected adipokines related to insulin regulation (adiponectin, visfatin, resistin).

METHODS

Data were collected from 12 healthy adult women. Each subject participated in two trials, 4 weeks apart. The first trial was reserved for resting measurements only (control trial), while the second trial involved a 45-min exercise (-15 % slope, ~60 % of VO2max) intervention (exercise trial). Insulin sensitivity (HOMA), creatine kinase activity (CK), delayed onset muscle soreness (DOMS), tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), glucose, insulin, adiponectin, resistin, and visfatin were assessed pre-exercise and 1, 2, 3, and 4 days post-exercise and during the same time points in the control trial.

RESULTS

Analyses revealed that CK, DOMS, TNF-α, IL-6, insulin and HOMA significantly increased (p < 0.05) throughout recovery (days 1-4). Adiponectin and visfatin remained unchanged, while resistin significantly increased (p < 0.05) only 2 days post-exercise. Visfatin was negatively correlated with HOMA at days 1 and 4 of recovery.

CONCLUSION

Although muscle damage due to downhill running caused a decline of insulin sensitivity, this response was not associated with the changes in adipokine levels.

Neuromuscular impairment following backpack load carriage

Load Carriage using backpacks is an occupational task and can be a recreational pursuit. The aim of this study was to investigate the mechanisms responsible for changes in neuromuscular function of the m. quadriceps femoris following load carriage. The physiological responses of 10 male participants to voluntary and electrically stimulated isometric contractions were measured before and immediately after two hours of treadmill walking at 6.5 km•h ⁻¹ during level walking with no load [LW], and level walking with load carriage (25 kg backpack) [LC]. Maximal voluntary contraction force decreased by 15 ± 11 % following LC (p=0.006), with no change following LW (p=0.292). Voluntary activation decreased after LW and LC (p=0.033) with no difference between conditions (p=0.405). Doublet contraction time decreased after both LW and LC (p=0.002), with no difference between conditions (p=0.232). There were no other changes in electrically invoked doublet parameters in either condition. The 20:50 Hz ratio did not change following LW (p=0.864) but decreased from 0.88 ± 0.04 to 0.84 ± 0.04 after LC (p=0.011) indicating reduced Ca2+ release from the sarcoplasmic reticulum during excitation contraction coupling. In conclusion, two hours of load carriage carrying a 25 kg back pack caused neuromuscular impairment through a decrease in voluntary activation (i.e. central drive) and fatigue or damage to the peripheral muscle, including impairment of the excitation contraction coupling process. This may reduce physical performance and increase the risk of musculoskeletal injury.

Exercise-induced muscle damage and running economy in humans

Running economy (RE), defined as the energy demand for a given velocity of submaximal running, has been identified as a critical factor of overall distance running performance. Plyometric and resistance trainings, performed during a relatively short period of time (~15-30 days), have been successfully used to improve RE in trained athletes. However, these exercise types, particularly when they are unaccustomed activities for the individuals, may cause delayed onset muscle soreness, swelling, and reduced muscle strength. Some studies have demonstrated that exercise-induced muscle damage has a negative impact on endurance running performance. Specifically, the muscular damage induced by an acute bout of downhill running has been shown to reduce RE during subsequent moderate and high-intensity exercise (>65% VO₂max). However, strength exercise (i.e., jumps, isoinertial and isokinetic eccentric exercises) seems to impair RE only for subsequent high-intensity exercise (~90% VO₂max). Finally, a single session of resistance exercise or downhill running (i.e., repeated bout effect) attenuates changes in indirect markers of muscle damage and blunts changes in RE.

The effects of strength training and endurance training order on running economy and performance

This study examined the acute effect of strength and endurance training sequence on running economy (RE) at 70% and 90% ventilatory threshold (VT) and on running time to exhaustion (TTE) at 110% VT the following day. Fourteen trained and moderately trained male runners performed strength training prior to running sessions (SR) and running prior to strength training sessions (RS) with each mode of training session separated by 6 h. RE tests were conducted at baseline (Base-RE) and the day following each sequence to examine cost of running (CR), TTE, and lower extremity kinematics. Maximal isometric knee extensor torque was measured prior to and following each training session and the RE tests. Results showed that CR at 70% and 90% VT for SR-RE (0.76 ± 0.10 and 0.77 ± 0.07 mL·kg(-0.75)·m(-1)) was significantly greater than Base-RE (0.72 ± 0.10 and 0.70 ± 0.11 mL·kg(-0.75)·m(-1)) and RS-RE (0.73 ± 0.09 and 0.72 ± 0.09 mL·kg(-0.75)·m(-1)) (P < 0.05). TTE was significantly less for SR-RE (237.8 ± 67.4 s) and RS-RE (275.3 ± 68.0 s) compared with Base-RE (335.4 ± 92.1 s) (P < 0.01). The torque during the SR sequence was significantly reduced for every time point following the strength training session (P < 0.05). However, no significant differences were found in torque following the running session (P > 0.05), although it was significantly reduced following the strength training session (P < 0.05) during the RS sequence. These findings show that running performance is impaired to a greater degree the day following the SR sequence compared with the RS sequence.

The effects of a downhill running bout on running economy

This study investigated whether downhill (DH) running (10-min @ 214.4 m·min(-1) and -10% grade) would elicit acute and delayed effects on running economy (RE) upon completion of DH running (RE2) and daily over 72 h (RE3, RE4, RE5). Fifteen runners (8 female, 7 male) completed the protocol. RE was measured during level running performed at 70% VO2peak. A baseline RE test (RE1) was used for comparison. Muscle soreness was significantly elevated at RE3 and RE4 vs. RE1. Oxygen uptake was significantly elevated at RE2 relative to RE3, RE4 and RE5 but was not different from RE1. Heart rate was similarly elevated at RE2. Measures of ankle, knee and hip joint angles at heel strike and toe off were not affected at any time-point in a subset of subjects (N = 6). A short DH running bout did not elicit significant delayed adverse effects on oxygen uptake or gait parameters relative to baseline.

Neuromuscular and cardiovascular responses of Royal Marine recruits to load carriage in the field

Cardiovascular and neuromuscular responses of 12 male Royal Marine recruits (age 22 ± 3 years, body mass 80.7 ± 6.8 kg, VO(2)max 52.3 ± 2.7 ml kg(-1) min(-1)) were measured during 19.3 km of load carriage walking at 4.2 km h(-1) and carrying 31.0 kg. Heart rate during load carriage was 145 ± 10 beats·min(-1) (64 ± 5 %HRR) and showed a negative relationship with body mass (r = -0.72, P = 0.009) but no relationship with VO(2)max (ml kg(-1) min(-1); r = -0.40, P = 0.198). Load carriage caused a decrease in vertical jump height (8 ± 9%) and power (5 ± 5%) (P < 0.001). Change in vertical jump power showed a positive relationship with body mass (r(2) = 0.40, P = 0.029) but no relationship to VO(2)max (ml kg(-1) min(-1); r(2) = 0.13, P = 0.257). In conclusion, load carriage caused a reduction in vertical jump performance (i.e. decreased neuromuscular function). Lighter individuals were disadvantaged when carrying absolute loads, as they experienced higher cardiovascular strain and greater decreases in neuromuscular function.

The effects of eccentric exercise-induced muscle damage on running kinematics at different speeds

This study investigated the effects of knee localised muscle damage on running kinematics at varying speeds. Nineteen young women (23.2 ± 2.8 years; 164 ± 8 cm; 53.6 ± 5.4 kg), performed a maximal eccentric muscle damage protocol (5 × 15) of the knee extensors and flexors of both legs at 60 rad · s(-1). Lower body kinematics was assessed during level running on a treadmill at three speeds pre- and 48 h after. Evaluated muscle damage indices included isometric torque, muscle soreness and serum creatine kinase activity. The results revealed that all indices changed significantly after exercise, indicating muscle injury. Step length decreased and stride frequency significantly increased 48 h post-exercise only at the fastest running speed (3 m · s(-1)). Support time and knee flexion at toe-off increased only at the preferred transition speed and 2.5 m · s(-1). Knee flexion at foot contact, pelvic tilt and obliquity significantly increased, whereas hip extension during stance-phase, knee flexion during swing-phase, as well as knee and ankle joints range of motion significantly decreased 48 h post-exercise at all speeds. In conclusion, the effects of eccentric exercise of both knee extensors and flexors on particular tempo-spatial parameters and knee kinematics of running are speed-dependent. However, several pelvic and lower joint kinematics present similar behaviour at the three running speeds examined. These findings provide new insights into how running kinematics at different speeds are adapted to compensate for the impaired function of the knee musculature following muscle damage.

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.

Effect of eccentric exercise-induced muscle damage on the dynamics of muscle oxygenation and pulmonary oxygen uptake

Unaccustomed eccentric exercise has a profound impact on muscle structure and function. However, it is not known whether associated microvascular dysfunction disrupts the matching of O2delivery (Q̇o2) to O2utilization (V̇o2). Near-infrared spectroscopy (NIRS) was used to test the hypothesis that eccentric exercise-induced muscle damage would elevate the muscle Q̇o2:V̇o2ratio during severe-intensity exercise while preserving the speed of the V̇o2kinetics at exercise onset. Nine physically active men completed “step” tests to severe-intensity exercise from an unloaded baseline on a cycle ergometer before (Pre) and 48 h after (Post) eccentric exercise (100 squats with a load corresponding to 70% of body mass). NIRS and breath-by-breath pulmonary V̇o2were measured continuously during the exercise tests and subsequently modeled using standard nonlinear regression techniques. There were no changes in phase II pulmonary V̇o2kinetics following the onset of exercise (time constant: Pre, 25 ± 4 s; Post, 24 ± 2 s; amplitude: Pre, 2.36 ± 0.23 l/min; Post, 2.37 ± 0.23 l/min; all P > 0.05). However, the primary (Pre, 14 ± 3 s; Post, 19 ± 3 s) and overall (Pre, 16 ± 4 s; Post, 21 ± 4 s) mean response time of the [HHb] response was significantly slower following eccentric exercise ( P < 0.05). The slower [HHb] kinetics observed following eccentric exercise is consistent with an increased Q̇o2:V̇o2ratio during transitions to severe-intensity exercise. We propose that unchanged primary phase V̇o2kinetics are associated with an elevated Q̇o2:V̇o2ratio that preserves blood-myocyte O2flux.

Isokinetic eccentric exercise of quadriceps femoris does not affect running economy

The purpose of this study was to investigate whether running economy is affected by isokinetic eccentric exercise designed to cause muscle damage. Twenty-four young healthy men performed 120 maximal voluntary eccentric actions at each thigh's quadriceps muscle at an angular velocity of 60 degrees .s. The participants were then randomly divided into 2 equal groups, 1 of which exercised 24 hours later, while the other group rested. Muscle damage indicators (i.e., serum creatine kinase, delayed onset muscle soreness, and eccentric, concentric, and isometric peak torque) and running economy indicators (i.e., oxygen consumption, pulmonary ventilation, respiratory exchange ratio, respiratory rate, and heart rate during treadmill running at 2.2 and 3.3 m.s) were assessed prior to and 48 hours following the eccentric exercise. All muscle damage indicators changed significantly in both groups (p < 0.05) in a way suggestive of considerable muscle damage. Running economy indicators of the exercise group demonstrated only an elevation of respiratory rate at 48 hours (p < 0.05) and a tendency to lower economy compared to the resting group. It can be concluded that isokinetic eccentric exercise applied to the quadriceps femoris muscles did not affect running economy 48 hours later and that resting during this period tended to result in more economical running compared to exercising at 24 hours.

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.