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North American Congress on Biomechanics Canadian Society for Biomechanics - American Society of Biomechanics University of Waterloo Waterloo, Ontario, Canada August 14-18, 1998 |
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North American Congress on Biomechanics Canadian Society for Biomechanics - American Society of Biomechanics University of Waterloo Waterloo, Ontario, Canada August 14-18, 1998 |
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THE EFFECT OF FATIGUE OF THE QUADRICEPS AND HAMSTRINGS DURING RUNNING
J.A. Mercer, L.A. Kindling, A.W. Arata, A. Hreljac, J. S. Dufek & B.T. Bates
Department of Exercise and Movement Science, University of Oregon
Eugene, OR 97403INTRODUCTION
Running performance is the result of the integration of several factors, for example, physiological, biomechanical, psychomotor, and biochemical factors (Cavanagh & Kram, 1985). When attempting to maximize run performance, the central nervous system must integrate the various systems in such a way to prevent or compensate for fatigue. As Bates, James and Osternig (1977) noted, "...fatigue is a factor that affects the breakdown of a movement pattern." The purpose of the present project was to investigate the effect of fatigue of specific muscular groups on running mechanics.
REVIEW AND THEORY
Fatigue has been defined as the "transient decrease of working capacity" (Asmussen, 1979) and will be discussed in the present paper as either muscular or system fatigue. Muscular fatigue would result from, for example, repeated maximal knee extensions. System fatigue would be the result of fatigue occurring concurrently in several systems, such as at the end of a 400 m sprint or marathon. Although there have been studies investigating the effects of system fatigue on running mechanics (e.g. Bates, et al., 1977; Elliot & Roberts, 1980), there are no known published data on the effect of muscular fatigue of specific muscle groups on running mechanics.
To better understand the effect of fatigue on performance, as well as the relative importance of different components of performance, running mechanics were compared during non-fatigued running and running following quadriceps and hamstrings fatigue (on different days). These muscles were selected due to the importance of the quadriceps and hamstrings (e.g. shock-attenuation, stability, propulsion) during running.
PROCEDURES
Five male (27 ±6.8 years; 83.3 ±7.19 kg; 1.85 ±0.03 m) experienced runners completed 2 tests, separated by at least 48 hours and no more than 1 week. Each test day consisted of a 3 minute non-fatigued run (NF) followed by a "fatigue protocol", designed to fatigue a specific muscle group bilaterally (either quadriceps or hamstrings). Using an isokinetic dynamometer, five consecutive maximal repetitions of the test muscle were completed. All testing/exercise was done with the subject seated and angular speed set at 30 deg· -1 . The peak torque value out of the 5 repetitions was recorded. The criteria for the number of repetitions to be completed within a set was 80% of this value (80PT). The fatigue protocol consisted of 8 sets of maximal contractions, with 45 seconds rest between sets. Within a set, repetitions were continued until the peak torque of 3 consecutive repetitions fell below 80PT. Order of muscle tested was randomized, and only one muscle was fatigued per test day.
Following muscular fatigue, subjects moved as quickly as possible to the treadmill (and did so in about 15 to 20 s) to complete another 3 minute run (Quadriceps Fatigued: QF; Hamstring Fatigued: HF). The run velocity was self selected and constant within a test day. For each run condition (NF, QF and HF), subjects started running while the treadmill belt was moving at the preferred speed. This resulted in subjects hanging onto the rails for about 1-3 strides. No data were analyzed during this period.
Knee angle was calculated from digitized markers (60 Hz) over 2 consecutive strides starting with the 5th stride. Digitized data from subject 5 were not included in the knee angle analysis due to problems with the reflective markers. Stride rate, calculated from 2 consecutive right heel contacts (30 Hz), was calculated over 25 consecutive strides during NF running, starting at the point where the subject released the hands from the handrails. During QF and HF, stride rate was calculated over 3 blocks of 25 strides. The first block of strides (t0) was calculated beginning at the point of handrail release. The second and third stride rate blocks were calculated starting at the 1 and 2 minute mark of fatigued running (t1 and t2, respectively).
RESULTS
Results of a repeated measures ANOVA, indicated no differences in maximum knee flexion (Table 1) between fatigue (QF or HF) and NF conditions during support or swing (p>0.05). There were no significant differences in stride rate between NF and HF running (Figure 1) across any blocks (i.e. NF, t0, t1, or t2) (p>0.05). Simple effects post hoc testing indicated that during QF (Figure 2), stride rate was increased during t0 vs NF (p<0.05); however, no differences were observed when comparing t1 and t2 vs NF (p>0.05).
Quad. Fatigue Ham. Fatigue Support Swing Support Swing NF 135.4 (9.55) 74.8 (6.47) 138.3 (7.44) 138.9 (6.91) F 137.6 (10.20) 76.9 (8.39) 80.4 (5.56) 80.7 (6.78) Table 1: Maximum knee flexion during support and swing phase during running.
Figure 1: Stride rate: NF vs HF
Figure 2: Stride rate: NF vs QF
DISCUSSION
The effect of muscular fatigue on stride rate was observed only during the first minute of running following quadriceps fatigue. There was no effect of muscular fatigue (either quadricep or hamstring) on maximal knee flexion during the support or swing phase of running. One possible explanation for the minimal muscular fatigue effect is that the fatigue protocol was not intense enough to elicit a change in running mechanics. On average, 11.7 ±2.42 repetitions were completed during the fatigue protocol for quadriceps, vs 10.8 ±1.56 repetitions for hamstrings. It is possible that a more intense fatigue protocol utilizing both concentric and eccentric exercises may elicit different results. However, the subjects were highly motivated athletes, and each related that the exercise was intense.
The increased stride rate during the first minute of running following quadriceps fatigue is evidence that the system made subtle adjustments to running mechanics to compensate for the fatigued quadriceps. During running, the quadriceps function in part to absorb the energy of ground impact through eccentric activity through midsupport (Winter, 1983). An explanation for the increased stride rate may be that adjustments were made to reduce the demand on the quadriceps. Derrick, Hamill, and Caldwell (1996) reported that the energy absorbed by the hip, knee and ankle during non-fatiged running was dependent on stride rate. Subjects ran at a constant speed, and changed stride rate to higher or lower rates compared to the preferred stride rate. It was reported that the level of impact was lower and the energy absorbed by the lower extremity was lower during the higher stride rates. The energy absorbed by each joint was dependent on stride rate relative to the preferred stride rate. At stride rates greater than preferred, most of the energy was absorbed by the knee and ankle. At stride rates lower than the preferred, most of the energy was absorbed by the knee (Derrick, et al., 1996).
During non-fatigued running, Hamill, Derrick, and Holt (1995) reported that the metabolic cost of running at a particular speed was minimized when subjects ran at a preferred stride rate. Interestingly, the shock attenuation was not minimized during running at the preferred stride rate. That is, the system optimized the metabolic cost but not the mechanical cost of running.
The increased stride rate during QF compared to NF running may be evidence that the system compensated for muscular fatigue by optimizing the mechanical cost of running but not the metabolic cost. This hypothesis has yet to be tested, but would appear to be tenable. Further research into the effects of muscular fatigue on running mechanics may lend insight as to how the system optimizes performance.
REFERENCES
Asmussen, E., MSSE, 11, 313-321, 1979.
Bates, B.T. et al., J Motor Behav, 9, 205-7, 1977.
Cavanagh & Kram, MSSE, 17, 304-308, 1985.
Derrick, et al., CSB, 9th Bi. Conf., 136-137, 1996.
Elliott & Roberts, Can. J. Appl. Spt. Sci., 5, 203-207.
Hamill, et al., Hum Mov Sci, 14, 45-60, 1995.
Winter, D., J. Biomech., 16, 91-97, 1983.