Approximately 25 runners were filmed at the 24.9- and 41.0-km points in the 1987 Everest Marathon. Their finishing times ranged from 4:53:10 to 7:14:37. Leg length, step lengths, step frequencies, knee angles at impact, and ankle-to-hip angles at impact were determined for each runner who appeared in both films (N = 20). The slopes at the two filming sites were −21.8% and −26.8%, considerably steeper gradients than have previously been studied. When compared to data from other downhill running studies at −10% gradient, these athletes had slightly slower speeds, shorter step lengths, straighter legs on impact, and greater minimum knee angles during stance. The results suggest that the runners used a variety of techniques to minimize the effects of ground impact while still allowing for the competitive aspect of the race, considerable variation in footing and terrain, and personal safety.
Robert N. Marshall, David J. Paterson and Paul Glendining
William M. Sherman, Julie M. Lash, John C. Simonsen and Susan A. Bloomfield
Because muscle damage from eccentric exercise has been associated with alterations in muscle glycogen metabolism, this study determined the effects of exercise on the insulin and glucose responses to an oral glucose tolerance test (OGTT). In a repeated-measures design, 11 subjects undertook either no exercise, 2 min of isokinetic leg exercise, or 50 min of level or downhill running. No exercise was performed and diet was controlled during the 48 hrs after the treatments and before the OGTT. Ratings of muscle soreness and CK activity were significantly elevated 48 hrs after downhill running. Level running also increased CK activity but did not induce muscle soreness. Isokinetic exercise did not affect either one. Blood glucose responses to the OGTT were similar among the treatments. In contrast, the insulin responses to the OGTT following downhill running were significantly increased. These results suggest that eccentric exercise associated with downhill running that results in delayed muscle soreness is associated with the development of a mild insulin-resistant condition.
Matthew R. Nelson, Robert K. Conlee and Allen C. Parcell
In Delayed Onset Muscle Soreness (DOMS), muscles become sore 24 to 48 hours after eccentric and unaccustomed activity. Fiber stiffness, due to decreased muscle glycogen, may predispose muscle to greater damage during eccentric exercise. This study sought to determine if inadequate carbohydrate intake following a protocol to decrease muscle glycogen would increase DOMS after 15 min of downhill running. Thirty-three male subjects (age, 18–35 years) were randomized into 3 groups for testing over a 7-day period. The depletion (DEP) group (n = 12) underwent a glycogen depletion protocol prior to a 15-min downhill run designed to induce DOMS. The repletion (FED) group (n = 10) underwent a glycogen depletion protocol followed by a carbohydrate repletion protocol (>80% CHO) prior to downhill running. The third (ECC) group (n = 11) performed only the downhill running protocol. Subjective muscle soreness, isometric force production, relaxed knee angle, and thigh circumference were measured pretreatment and on days 1, 2, 3, 4, and 6 post treatment. Subjective muscle soreness for all groups increased from 0 cm pretreatment to 3.05 ± 0.72 cm (on a 10-cm scale) on day 1 post treatment (p < .05). All groups were significantly different from baseline measurements until day 4 post treatment. Each group experienced a decline in isometric force from 281 ± 45 N pre-to 253 ± 13 N on day 1 post treatment (p < .05). The decrease in isometric force persisted in all groups for 4 days post treatment. Increases in thigh circumference and relaxed knee angle elevations in all 3 groups were statistically different (p < .05) from pretreatment until day 4. No differences were noted between groups for any of the parameters examined. In the current study, 15 min of downhill running is sufficient to cause DOMS with the associated functional and morphological changes; however, inadequate carbohydrate intake after a glycogen depleting exercise does not appear to exacerbate DOMS and the associated symptoms.
Matthew David Cook, Stephen David Myers, John Stephen Michael Kelly and Mark Elisabeth Theodorus Willems
Impaired glucose tolerance was shown to be present 48 hr following muscle-damaging eccentric exercise. We examined the acute effect of concentric and muscle-damaging eccentric exercise, matched for intensity, on the responses to a 2-hr 75-g oral glucose tolerance test (OGTT). Ten men (27 ± 9 years, 178 ± 7 cm, 75 ± 11 kg, VO2max: 52.3 ± 7.3 ml·kg-1·min-1) underwent three OGTTs after an overnight 12 hr fast: rest (control), 40-min (5 × 8-min with 2-min interbout rest) of concentric (level running, 0%, CON) or eccentric exercise (downhill running, –12%, ECC). Running intensity was matched at 60% of maximal metabolic equivalent. Maximal isometric force of m. quadriceps femoris of both legs was measured before and after the running protocols. Downhill running speed was higher (level: 9.7 ± 2.1, downhill: 13.8 ± 3.2 km·hr-1, p < .01). Running protocols had similar VO2max (p = .59), heart rates (p = .20) and respiratory exchange ratio values (p = .74) indicating matched intensity and metabolic demands. Downhill running resulted in higher isometric force deficits (level: 3.0 ± 6.7, downhill: 17.1 ± 7.3%, p < .01). During OGTTs, area-under-the-curve for plasma glucose (control: 724 ± 97, CON: 710 ± 77, ECC: 726 ± 72 mmol·L-1·120 min, p = .86) and insulin (control: 24995 ± 11229, CON: 23319 ± 10417, ECC: 21842 ± 10171 pmol·L-1·120 min, p = .48), peak glucose (control: 8.1 ± 1.3, CON: 7.7 ± 1.2, ECC: 7.7 ± 1.1 mmol·L-1, p = .63) and peak insulin levels (control: 361 ± 188, CON: 322 ± 179, ECC: 299 ± 152 pmol·L-1, p = .30) were similar. It was concluded that glucose tolerance and the insulin response to an OGTT were not changed immediately by muscle-damaging eccentric exercise.
Michael S. Green, J. Andrew Doyle, Christopher P. Ingalls, Dan Benardot, Jeffrey C. Rupp and Benjamin T. Corona
This study determined whether disrupted glucose and insulin responses to an oral glucose-tolerance test (OGTT) induced by eccentric exercise were attenuated after a repeated bout. Female participants (n = 10, age 24.7 ± 3.0 yr, body mass 64.9 ± 7.4 kg, height 1.67 ± 0.02 m, body fat 29% ± 2%) performed 2 bouts of downhill running (DTR 1 and DTR 2) separated by 14 d. OGTTs were administered at baseline and 48 hr after DTR 1 and DTR 2. Maximum voluntary isometric quadriceps torque (MVC), subjective soreness (100-mm visual analog scale), and serum creatine kinase (CK) were assessed pre-, post-, and 48 hr post-DTR 1 and DTR 2. Insulin and glucose area under the curve (38% ± 8% and 21% ± 5% increase, respectively) and peak insulin (44.1 ± 5.1 vs. 31.6 ± 4.0 μU/ml) and glucose (6.5 ± 0.4 vs. 5.5 ± 0.4 mmol/L) were elevated after DTR 1, with no increase above baseline 48 hr after DTR 2. MVC remained reduced by 9% ± 3% 48 hr after DTR 1, recovering back to baseline 48 hr after DTR 2. Soreness was elevated to a greater degree 48 hr after DTR 1 (48 ± 6 vs. 13 ± 3 mm), with a tendency for greater CK responses 48 hr after DTR 1 (813 ± 365 vs. 163 ± 43 U/L, p = .08). A novel bout of eccentric exercise confers protective effects, with subsequent bouts failing to elicit disruptions in glucose and insulin homeostasis.
Jeffrey J. Chu and Graham E. Caldwell
Studies on shock attenuation during running have induced alterations in impact loading by imposing kinematic constraints, e.g., stride length changes. The role of shock attenuation mechanisms has been shown using mass-spring-damper (MSD) models, with spring stiffness related to impact shock dissipation. The present study altered the magnitude of impact loading by changing downhill surface grade, thus allowing runners to choose their own preferred kinematic patterns. We hypothesized that increasing downhill grade would cause concomitant increases in both impact shock and shock attenuation, and that MSD model stiffness values would reflect these increases. Ten experienced runners ran at 4.17 m/s on a treadmill at surface grades of 0% (level) to 12% downhill. Accelerometers were placed on the tibia and head, and reflective markers were used to register segmental kinematics. An MSD model was used in conjunction with head and tibial accelerations to determine head/arm/trunk center of mass (HATCOM) stiffness (K1), and lower extremity (LEGCOM) stiffness (K2) and damping (C). Participants responded to increases in downhill grade in one of two ways. Group LowSA had lower peak tibial accelerations but greater peak head accelerations than Group HighSA, and thus had lower shock attenuation. LowSA also showed greater joint extension at heelstrike, higher HATCOM heelstrike velocity, reduced K1 stiffness, and decreased damping than HighSA. The differences between groups were exaggerated at the steeper downhill grades. The separate responses may be due to conflicts between the requirements of controlling HATCOM kinematics and shock attenuation. LowSA needed greater joint extension to resist their higher HATCOM heelstrike velocities, but a consequence of this strategy was the reduced ability to attenuate shock with the lower extremity joints during early stance. With lower HATCOM impact velocities, the HighSA runners were able to adopt a strategy that gave more control of shock attenuation, especially at the steepest grades.
Nicola Giovanelli, Lea Biasutti, Desy Salvadego, Hailu K. Alemayehu, Bruno Grassi and Stefano Lazzer
downhill running induce muscle damage and neuromuscular alterations, with a decreased central drive and strength loss. 24 In fact, UT induces muscle damage and inflammation which could affect the contractility properties and oxidative metabolism. 21 Thus, the repeated downhill sections occurred during
Thomas M. Doering, Peter R. Reaburn, Nattai R. Borges, Gregory R. Cox and David G. Jenkins
Following exercise-induced muscle damage (EIMD), masters athletes take longer to recover than younger athletes. The purpose of this study was to determine the effect of higher than recommended postexercise protein feedings on the recovery of knee extensor peak isometric torque (PIT), perceptions of recovery, and cycling time trial (TT) performance following EIMD in masters triathletes. Eight masters triathletes (52 ± 2 y, V̇O2max, 51.8 ± 4.2 ml•kg-1•min-1) completed two trials separated by seven days in a randomized, doubleblind, crossover study. Trials consisted of morning PIT testing and a 30-min downhill run followed by an eight-hour recovery. During recovery, a moderate (MPI; 0.3 g•kg-1•bolus-1) or high (0.6 g•kg-1•bolus-1) protein intake (HPI) was consumed in three bolus feedings at two hour intervals commencing immediately postexercise. PIT testing and a 7 kJ•kg-1 cycling TT were completed postintervention. Perceptions of recovery were assessed pre- and postexercise. The HPI did not significantly improve recovery compared with MPI (p > .05). However, comparison of within-treatment change shows the HPI provided a moderate beneficial effect (d = 0.66), attenuating the loss of afternoon PIT (-3.6%, d = 0.09) compared with the MPI (-8.6%, d = 0.24). The HPI provided a large beneficial effect (d = 0.83), reducing perceived fatigue over the eight-hour recovery (d = 1.25) compared with the MPI (d = 0.22). Despite these effects, cycling performance was unchanged (HPI = 2395 ± 297 s vs. MPI = 2369 ± 278 s; d = 0.09). In conclusion, doubling the recommended postexercise protein intake did not significantly improve recovery in masters athletes; however, HPI provided moderate to large beneficial effects on recovery that may be meaningful following EIMD.
David C. Nieman, Courtney L. Capps, Christopher R. Capps, Zack L. Shue and Jennifer E. McBride
included 30 min of −10% downhill running. Methods Participants Recruitment was conducted through direct messages to runners in Charlotte, NC, metropolitan area. Participants included 20 male and female runners (aged 22–45 years) who regularly competed in long-distance road races and were capable of running
Lauri M. Webber, William C. Byrnes, Thomas W. Rowland and Vicky L. Foster
Although delayed onset muscle soreness and increased serum creatine kinase activity (SCKA) following unaccustomed exercise is common in adults, little is known concerning these responses in children. The perception of muscle soreness and SCKA in children (n = 16) (M age = 10.4±.30 yr) was compared to a control group of adults (n = 15) (M age = 27.1±.87 yr) following a single bout of downhill running (30 min − 10% grade). Preexercise SCKA was not significantly different between the children (91.7±8.5 μmol•L−1•min−1) and the adults (77.1±5.9 μmol•L−1•min−1). The difference in SCKA (pre to 24 hours post) was significantly less (p<.01) for the children (68.6±16.2 μmol•L−1•min−1) than for the adults (188.7±36.8 μmol•L−1•min−1). When the groups were adjusted for weight differences, SCKA was not significantly different between the adults and the children. Regardless of age, males demonstrated a significantly greater increase in SCKA postexercise when compared to females. Soreness ratings (verbally anchored scale from 1 to 10) 24 hours following the downhill run were not significantly different between the children (3.8±.6) and the adults (4.5±.7). Following an eccentrically biased exercise task, children exhibited less of a SCKA response compared to adults that is related to body weight.