Competitive rock climbing places unique physiological demands on the body. Intermittent isometric handgrip contractions are required to prevent falling and as fixators to enable larger arm muscles to provide upward propulsion (22). Progression up the wall thus requires high-force isometric handgrip contractions, performed intermittently for 3-6 minutes in total to complete the climb (27). For example, average handgrip forces of >300 N per hand in a two-handed static climbing posture on a vertical wall have been observed (13), and yet greater handgrip forces will be required with a single hand posture on an overhanging wall or if the climber wishes to move upward. Typical handgrip duty cycle (the time spent contracting divided by the time spent relaxed) and contraction time during competitive rock climbing have yet to be documented in a reliable scientific study. However, as at least one hand must be holding on at all times, the duty cycle must be greater than 50%. Previous laboratory-based studies simulating rock climbing have used 5-second contractions with 5-second rests (14), 5-second contractions with 2-second rests (11), and a single sustained contraction (10). Maximal voluntary contraction (MVC) handgrip force decreases by >28% after maximal climbing exercise (26).
In an intermittent isometric handgrip exercise such as climbing, forearm blood flow is partially or completely occluded during contraction and may be inadequate to meet oxygen demand and clear metabolic waste. Barnes (1) demonstrated that forearm blood flow during sustained isometric contractions was completely occluded at a handgrip force of about 340 N regardless of the MVC force of the subject. Many studies show very large postcontraction hyperemia even after isometric contractions of much less than a force of 340 N (7,11,19,24,28,31-33), implying that blood flow during contraction is insufficient to meet metabolic needs. Thus, the rate of fatigue development is likely to be related to the ability to maximize blood flow between contractions. There is some evidence in support of this (23,33), showing perfusion pressure, and presumably muscle blood supply, affect intermittent isometric exercise performance.
Repeated bouts of intermittent isometric contractions, such as occurring during rock climbing training, have specific effects on blood flow in the trained muscles independent of those changes in capillary density usually found with dynamic endurance training. These include attenuated muscle sympathetic nerve activity during isometric forearm exercise (21) and decreased sympathetic pressor response to isometric plantar flexion exercise (5), suggesting increased local vasodilation in the trained muscle. These results are further supported by studies that observed enhanced vasodilatory capacity in the forearms of tennis players (18) and manual workers (20) compared with untrained individuals. Compared with the untrained population, elite rock climbers have greater forearm blood flow and twice the time to fatigue during intermittent isometric handgrip exercise, but not continuous isometric handgrip exercise (11), suggesting that the greater endurance of elite rock climbers is related to blood flow between contractions.
In an attempt to further increase forearm blood flow and speed recovery during a rock climb, an active recovery technique called “shaking out” has become a common rock climbing practice. Whenever the terrain allows the rock climber to adopt a resting stance, the climber will shake the resting hand as if trying to flick water from the fingertips. Anecdotally, this is reported to speed recovery and improve climbing performance by increasing blood flow. Another recovery technique, low-frequency vibration, has been shown to increase muscle blood flow (6,12,34) so also may have beneficial effects on climbing performance.
The primary aim of this study was to test the hypothesis that recovery strategies of shaking out and low-frequency forearm vibration during the rest periods increase intermittent isometric handgrip exercise performance. The secondary aim was to determine whether this increase in intermittent isometric handgrip exercise performance was different in trained vs. untrained climbers. Finally, it was also hypothesized that any effects of recovery strategy or training status would be abolished by restriction of blood flow during the rest periods.
Experimental Approach to the Problem
Two groups of subjects were recruited: trained climbers from the local university sport climbing club and untrained subjects from the general student body. To determine the effect of recovery techniques during exercise, subjects completed a simulated rock climb by performing controlled sets of handgrip contractions on a specially modified handgrip exerciser. Between sets, subjects performed different recovery techniques: shaking out, low-frequency vibration, or passive rest. Each recovery technique was performed with and without forearm occlusion, giving a total of 6 interventions. Handgrip MVC was measured before and after each simulated rock climb to determine the decrement in strength. A 20-contraction time trial was performed after the post-climb MVC test as a relative measure of post-climb handgrip power.
A total of 18 subjects took part in this study. Nine male indoor rock climbers (mean [minimum-maximum], age 23 [19-32] years, body mass 72 [63-82] kg, height 1.77 [1.69-1.83] m) who trained at least 4 days per week were recruited from the local university sport climbing club. All had at least 3 years of climbing training history and did not perform any other form of upper-body training. Nine untrained participants were recruited from the student population at the university (5 men and 4 women, age 23 [19-32] years, body mass 74 [54-125] kg, height 1.76 [1.65-1.93) m). Untrained participants had no rock climbing experience and had not undertaken any handgrip-specific training for at least 12 months before the study. Subjects were informed of the experimental risks and signed an informed consent document before the investigation. The investigation was approved by an institutional review board for use of human subjects and complied with the Declaration of Helsinki.
After completing a familiarization session, each subject performed 6 trial sessions each separated by a minimum of 48 hours. All sessions were performed at 20-22° C at sea level. Testing was performed during winter when the trained climbers performed all their training indoors. Subjects were required to refrain from strenuous handgrip exercise for 48 hours before each session. Each session consisted of (a) a pre-MVC test, followed by (b) a fixed workload fatiguing exercise bout including electromyogram (EMG) recording, (c) a post-MVC test, and finally (d) a 20-contraction time trial (Figure 1).
MVC Tests (a) and (c)
The MVC test required the subject to perform 3 maximal voluntary handgrip contractions on an electronic grip strength transducer (ADInstruments, Sydney, Australia). The largest of the 3 force values was recorded as MVC force. This test has been previously shown to reliably and significantly measure indoor climbing performance (25).
Fixed Workload Fatiguing Exercise Bout (b)
The fixed workload fatiguing exercise was performed using a custom handgrip exerciser with a switch to detect when the exerciser was fully closed (Figure 2). This switch was interfaced with a POWERLAB 4ST (ADInstruments), and the resulting signal was recorded using CHART 5 software (ADInstruments). Three different handgrip exercisers with different spring stiffness (106, 148, and 196 N) were used to produce a similar relative handgrip force between subjects. Subjects sat with the dominant arm hanging vertically in the functional position and the handgrip exerciser held in the dominant hand. Subjects completed sets consisting of six 3-second contractions with 1-second rest. Each set was separated by 9-second rest periods. The recovery interventions were performed during the 9-second rest periods. For each contraction, the subject closed the handgrip exerciser to activate the switch, then held the switch closed for the duration of the contraction. A computer program provided the subject with visual and audio cues to indicate when the switch was closed and to get ready, contract, relax, or perform the resting intervention. To maintain the same relative intensity between subjects, the difficulty of the fixed workload fatiguing exercise was tailored to each subject during the initial familiarization session. Subjects were allocated the easy, medium, or hard handgrip exerciser depending on their MVC force. Subjects then performed between 5 and 11 sets (30-66 contractions) intended to reduce their post-exercise handgrip MVC force to 70% of the pre-exercise force. If the post-exercise force was not between 65 and 75% of pre-exercise force, then the number of contractions was revised and the subject allowed 30-minute rest before attempting the revised target. The number of contractions required became that subject's designated target for all subsequent testing sessions.
One of the 3 different recovery strategies was performed during each fixed workload fatiguing exercise bout: active recovery (SHAKE), with the subjects shaking their arm during the rest period, designed to mimic the shaking out action commonly used by rock climbers; vibration (VIB), with the subject's hand resting on a vibration device vibrating at 12.5 Hz (Galileo Top; Novotec Medical, Pforzheim, Germany), designed to vibrate the forearm tissue at a frequency previously shown to increase blood flow (34); and a control of passive recovery (PAS), with the subjects resting their arm passively by their side.
To isolate the effects of the recovery strategies on blood flow, recovery was performed with either free blood flow (FREE) or with occlusion (OCCL). Occlusion was performed using a blood pressure cuff inflated about the bicep during the rest periods. The cuff was inflated manually to 240 mm Hg. Inflation was completed within 3 seconds of the beginning of the rest period. Thus, if a recovery strategy affected performance by altering blood flow, this effect would only be seen in the FREE interventions.
In total, subjects performed 2 × 3 = 6 interventions: PAS/FREE, SHAKE/FREE, VIB/FREE, PAS/OCCL, SHAKE/OCCL, and VIB/OCCL. Each subject performed each intervention once in a balanced randomly allocated order.
Electromyogram Recording (b)
Recordings for all trials were made from the skin above the flexor carpi radialis (FCR) muscle of the right forearm. Surface EMGs were obtained via two 16-mm-diameter self-adhesive electrodes 40 mm apart and centered about the midpoint of the FCR. The FCR was located by palpitation while the subjects adducted their middle finger against the desk. To allow accurate placement of the electrodes in subsequent sessions, electrode positions were marked with permanent marker and subjects were requested to remark the positions after bathing. An earth electrode was also placed at the transverse carpal ligament of the right wrist. Electromyogram signals were preamplified (Bioamp; ADInstruments), filtered (1-5 kHz with a 50 Hz notch), digitized (POWERLAB 4ST, 1 kHz sampling rate), and recorded in a personal computer (CHART 5; ADInstruments). Root mean square (RMS) values were calculated for the stationary portion (i.e., while the switch on the handgrip exerciser was held closed) of the last contraction of each set of the fixed workload fatiguing exercise bout.
20-Contaction Time Trial (TT20) Test (d)
The 20-contraction time trial involved the subject fully closing the handgrip exerciser 20 times as fast as possible. The time was recorded from the start of the first closed period to the start of the 20th closed period. The computer recorded the time taken for 20 contractions and provided visual feedback to indicate when the exerciser was fully closed.
All results are presented as mean (SD). Statistical significance level was set at 0.05 for all tests.
To determine whether trained and untrained participants performed a similar number of contractions in the fixed workload fatiguing exercise, a 2-tailed independent sample t-test was performed between each group's designated targets.
To test the effects of recovery strategy, occlusion, and training status on TT20, an analysis of variance (ANOVA) analysis was performed with a between-subject factor of training status and within-subject factor of recovery strategy (PAS, SHAKE, or VIB) and occlusion (FREE or OCCL). For MVC measurements, a within-trial (repeated) factor of pre-exercise vs. post-exercise was included. Third-order interaction factors were also included in the models. To test the effects of recovery strategy, occlusion, and training status on EMG signal, the time each contraction occurred was normalized to the total time of the fatiguing exercise bout. An analysis of covariance (ANCOVA) was then performed with a between-subject factor of training status, within-subject factor of recovery strategy and occlusion, and a covariate of normalized time. Where significance was found, t-tests with Tukey's adjustment for multiple tests were used to locate the differences, and the intraclass correlation coefficients derived from the within-intervention and between-intervention means of squares were computed. Least squares means were used to generate estimators of the population means.
There were no significant first-order differences between trained and untrained in the number of contractions performed (42 [SD 7] vs. 41 [SD 11], p > 0.05), the fraction of MVC force required to close the handgrip tester (35% [SD 6%] vs. 33% [SD 6%], p > 0.05), TT20 time (26 [SD 20] seconds vs. 21 [SD 16] seconds, p > 0.05), or RMS EMG signal (1.52 [SD 0.61] mV vs. 1.38 [SD 0.57] mV, p > 0.05), indicating suitable prescription of spring stiffness and number of contractions giving the same relative intensity for both trained and untrained groups. There were no significant first-order or interaction effects of shaking out or low-frequency vibration on any of the variables measured (MVC, TT20, and EMG all p > 0.05, Table).
MVC Tests (a) and (c)
The trained group exhibited significantly greater MVC than untrained both before (559 [SD 72] N vs. 450 [SD 133] N, p < 0.01) and after (371 [SD 90] N vs. 322 [SD 91] N, p < 0.01) fatiguing exercise. Reflecting the differences in absolute MVC between groups, there were differences in the spring stiffness of the handgrip testers allocated to each group (trained: 1 medium and 8 hard; untrained: 3 soft, 4 medium, and 2 hard). The ANOVA of MVC data (R 2 = 0.87) revealed a significant interaction effect of training status and occlusion, with the trained group having a significantly larger decrement in MVC than untrained only when occlusion was applied (Figure 3, p < 0.05, intraclass correlation coefficient = 0.39). Individual subject's handgrip MVC results for each resting intervention are shown in Figure 4.
Electromyogram Test (b)
As expected, the EMG ANCOVA (R 2 = 0.72) revealed that EMG signal increased throughout the fatiguing protocol (p < 0.001, intraclass correlation coefficient = 0.97), and this increase is augmented by occlusion (p < 0.01, Figure 5, intraclass correlation coefficient = 0.38). Interestingly, the increase in EMG with occlusion is greater in the trained group than in untrained (p < 0.01, Figure 5, intraclass correlation coefficient = 0.36).
TT20 Test (d)
The TT20 ANOVA (R 2 = 0.69) shows a significant interaction between training status and occlusion (p < 0.01, intraclass correlation coefficient = 0.46). Although there is no difference in TT20 times between groups when free blood flow is allowed, the trained group has significantly greater TT20 time than untrained when occlusion is applied during the recovery periods (Figure 6). Individual subject's TT20 times for each resting intervention are shown in Figure 4.
The primary finding of this study is that neither shaking out nor low-frequency vibration significantly improve intermittent isometric handgrip exercise capacity compared with passive rest. This corresponds with the findings of previous research that show no effect of low-frequency vibration on forearm blood flow (4,9). Shaking out is regularly performed by climbers between maneuvres with the aim of delaying fatigue in the forearm muscles. However, as there is no performance benefit from this technique, rock climbers should be advised to optimize their resting postures rather than performing this recovery strategy.
Anecdotal reports suggested that shaking out would improve recovery and performance by increasing forearm blood flow during recovery. A similar mechanism could be proposed for low-frequency vibration (12,34). The results of the present study show that these recovery modalities do not affect performance. Given that reduced perfusion pressure decreases intermittent isometric exercise performance (23,33), it seems likely that shaking out and low-frequency vibration do not affect forearm blood flow. However, as no blood flow measurements were taken in the present study, the possibility remains that the active recovery strategies did increase blood flow but that this increased blood flow had no effect on performance.
The handgrip exercisers and the handgrip dynamometer used in this study do not simulate all the handgrip positions that are encountered during rock climbing. In fact, there are a wide variety of handgrip positions employed in rock climbing as each different handhold requires a different hand position to achieve optimal grip strength. Due to the wide variety of handgrip positions required in rock climbing, we felt that the handgrip exercisers and handgrip dynamometer used would have adequate specificity for the findings to be applied to a real rock climbing situation. This is supported by the greater handgrip MVC of the trained group compared with untrained in this study and the correlation between handgrip strength and climbing performance observed by Wall et al. (25).
A notable finding of this study is that the increased intermittent handgrip exercise capacity shown by trained rock climbers is abolished if adequate blood flow does not occur during the recovery periods. The MVC tests (a) and (c) and the TT20 (d) are all direct measures of performance, and all show a significantly greater effect of occlusion on the trained group than untrained. The greater rate of EMG signal increase in the trained group (b) during constant force contractions with occlusion indicates that the performance decrement results from a higher level of peripheral fatigue as more motor units are recruited to generate the same force. We can thus infer that, compared with untrained subjects, the performance of trained climbers is more dependent on recovery blood flow. This finding corresponds with that of Fergusson and Brown (11) who show that trained rock climbers have greater endurance than untrained at the same relative intensity of intermittent isometric handgrip exercise but not in continuous isometric handgrip exercise.
Blood flow may influence fatigue by a variety of mechanisms. Restricted blood flow presents limits to oxygen delivery to the muscle and to the removal of various contraction by-products including H+ (2,8), Pi (29), Mg++ (3,30), and reactive oxygen species (15-17). All these factors are potential candidates for peripheral fatigue mechanisms. As intermittent isometric contractions present a challenging situation to the body's blood supply mechanisms, it is not surprising that training for this mode of exercise results in adaptations that allow increased recovery blood flow and therefore allow adequate oxygen supply and metabolite removal at higher contraction intensities and higher duty cycles.
Previous research has demonstrated enhanced vasodilatory capacity in isometrically trained muscles (18,20) and decreased sympathetic nervous pressor response (5,21) with intermittent isometric training, independent of the increases in vascularity usually observed with endurance training. Taken in conjunction with trained rock climbers' greater dependence on recovery blood flow demonstrated by the present study, these results suggest that the greater intermittent isometric handgrip exercise capacity of the trained group may be attributable to trained rock climber's enhanced vasodilatory capacity and the higher blood flows this allows during the rest periods.
Another potential explanation of the results of this study is that the trained and untrained groups had different levels of restriction to blood flow during the fixed workload contractions. As the untrained group used lower absolute force than the trained group (i.e., the same relative intensity), they may have had a greater forearm blood flow and be more able to provide substrate and clear waste metabolites during contraction. Furthermore, at lower contraction forces, untrained subjects are likely to consume less substrate and produce less waste. As such, untrained subjects would require less recovery blood flow so are likely to be less affected by occlusion during recovery. Further studies including blood flow measurement are needed if the relative importance of these 2 potential mechanisms is to be determined.
Trained rock climbers exhibit greater intermittent isometric handgrip exercise capacity than untrained individuals, but this greater capacity is dependent on blood flow during the recovery periods. Despite this, active recovery strategies of shaking out and low-frequency vibration aimed at increasing forearm blood flow have little effect on intermittent isometric handgrip exercise performance. Rock climbers and their coaches are therefore advised to focus on optimizing body position to minimize handgrip force at resting stances rather than compromising body position to allow for shaking out. This is particularly important for highly trained climbers who are reliant on forearm blood flow during rest periods.
This study was funded by Massey University. The authors have no financial or other interest in the results of this study. The results of the present study do not constitute endorsement of any product by the authors or the National Strength and Conditioning Association.
1. Barnes, WS. The relationship between maximum isometric strength and intramuscular circulatory occlusion. Ergonomics
23: 351-357, 1980.
2. Bergstrom, J, Harris, R, Hultman, E, and Nordesjo, L. Energy rich phosphagens in dynamic and static work. Adv Exp Med Biol
11: 341-355, 1971.
3. Blazev, R and Lamb, GD. Low [ATP] and elevated [Mg2+] reduce depolarization-induced Ca2+ release in rat skinned skeletal muscle fibres. J Physiol
520: 203-215, 1999.
4. Bovenzi, M, Lindsell, CJ, and Griffin, MJ. Acute vascular responses to the frequency of vibration
transmitted to the hand. J Occup Environ Med
57: 422-430, 2000.
5. Carrington, CA, Fisher, W, and White, MJ. The effects of athletic training and muscle contractile character on the pressor response to isometric exercise of the human triceps surae. Eur J Appl Physiol Occup Physiol
80: 337-343, 1999.
6. Cochrane, DJ and Hawke, EJ. Effects of acute upper-body vibration
on strength and power variables in climbers. J Strength Cond Res
21: 527-531, 2007.
7. Degens, H, Salmons, S, and Jarvis, JC. Intramuscular pressure, force and blood flow
in rabbit tibialis anterior muscles during single and repetitive contractions. Eur J Appl Physiol Occup Physiol
78: 13-19, 1998.
8. Edwards, RHT. Human muscle function and fatigue
. In: Human Muscle Fatigue: Physiological Mechanisms
. Porter, R and Whelan, J, eds. London, United Kingdom: Pittman Medical Ltd., 1981. pp. 1-18.
9. Egan, C, Espie, B, McGrann, S, McKenna, K, and Allen, J. Acute effects of vibration
on peripheral blood flow
in healthy subjects. J Occup Environ Med
53: 663-669, 1996.
10. Felici, F, Rosponi, A, Sbriccoli, P, Scarcia, M, Bazzucchi, I, and Iannattone, M. Effect of human exposure to altitude on muscle endurance during isometric contractions. Eur J Appl Physiol
85: 507-512, 2001.
11. Ferguson, RA and Brown, MD. Arterial blood pressure and forearm vascular conductance responses to sustained and rhythmic isometric exercise and arterial occlusion in trained rock climbers and untrained sedentary subjects. Eur J Appl Physiol
76: 174-180, 1997.
12. Kerschan-Schindl, K, Grampp, S, Henk, C, Resch, H, Preisinger, E, Fialka-Moser, V, and Imhof, H. Whole-body vibration
exercise leads to alterations in muscle blood volume. Clin Physiol
21: 377-382, 2001.
13. Quaine, F and Martin, L. A biomechanical study of equilibrium in sport rock climbing
. Gait Posture
10: 233-239, 1999.
14. Quaine, F, Vigouroux, L, and Martin, L. Finger flexors fatigue
in trained rock climbers and untrained sedentary subjects. Int J Sports Med
24: 424-427, 2003.
15. Reid, MB, Haack, KE, Franchek, KM, Valberg, PA, Kobzik, L, and West, MS. Reactive oxygen in skeletal muscle. I. Intracellular oxidant kinetics and fatigue
in vitro. J Appl Physiol
73: 1797-1804, 1992.
16. Reid, MB, Khawli, FA, and Moody, MR. Reactive oxygen in skeletal muscle. III. Contractility of unfatigued muscle. J Appl Physiol
75: 1081-1087, 1993.
17. Reid, MB, Shoji, T, Moody, MR, and Entman, ML. Reactive oxygen in skeletal muscle. II. Extracellular release of free radicals. J Appl Physiol
73: 1805-1809, 1992.
18. Sinoway, LI, Musch, TI, Minotti, JR, and Zelis, R. Enhanced maximal metabolic vasodilatation in the dominant forearms of tennis players. J Appl Physiol
61: 673-678, 1986.
19. Sjogaard, G, Savard, G, and Juel, C. Muscle blood flow
during isometric activity and its relation to muscle fatigue
. Eur J Appl Physiol
57: 327-335, 1988.
20. Smolander, J. Capacity for vasodilatation in the forearms of manual and office workers. Eur J Appl Physiol
69: 163-167, 1994.
21. Somers, V, Leo, K, Sheilds, R, Clary, M, and Mark, A. Forearm endurance training attenuates sympathetic nerve response to isometric handgrip training in normal humans. J Appl Physiol
72: 1039-1043, 1992.
22. Steel, AW. Physiology of sport rock climbing
. Br J Sports Med
38: 355-359, 2004.
23. Tachi, M, Kouzaki, M, Kanehisa, H, and Fukunaga, T. The influence of circulatory difference on muscle oxygenation and fatigue
during intermittent static dorsiflexion. Eur J Appl Physiol
91: 682-688, 2004.
24. Van Beekvelt, MCP, Colier, WNJM, Wevers, RA, and Van Engelen, BGM. Performance of near-infrared spectroscopy in measuring local O2 consumption and blood flow
in skeletal muscle. J Appl Physiol
90: 511-519, 2001.
25. Wall, CB, Starek, JE, Fleck, SJ, and Byrnes, WC. Prediction of indoor climbing performance in women rock climbers. J Strength Cond Res
18: 77-83, 2004.
26. Watts, P and Drobish, K. Physiological responses to simulated rock climbing
at different angles. Med Sci Sports Exerc
30: 1118-1122, 1998.
27. Werner, I and Gebert, W. Blood lactate responses to competitive climbing. In: Proceedings of the First International Conference on Science and Technology in Climbing and Mountaineering
. Messenger, N, Patterson, W, and Brook, D, eds. Leeds, 1999. chap 3 (CD-ROM).
28. Wesche, J. The time course and magnitude of blood flow
changes in the human quadraceps muscles following isometric contraction. J Physiol
377: 445-462, 1986.
29. Westerblad, H and Allen, DG. Changes of myoplasmic calcium concentration during fatigue
in single mouse muscle fibres. J Gen Physiol
98: 615-635, 1991.
30. Westerblad, H and Allen, DG. Myoplasmic free Mg2+ concentration during repetitive stimulation of single fibres from mouse skeletal muscle. J Physiol
453: 413-434, 1992.
31. Wigmore, DM, Propert, K, and Kent-Braun, JA. Blood flow
does not limit skeletal muscle force production during incremental isometric contractions. Eur J Appl Physiol
96: 370-378, 2006.
32. Williams, CA and Lind, AR. Measurement of forearm blood flow
by venous occlusion plethysmography: Influence of hand blood flow
during sustained and intermittent isometric exercise. Eur J Appl Physiol
42: 141-149, 1979.
33. Wright, JR, McCloskey, DI, and Fitzpatrick, RC. Effects of muscle perfusion pressure on fatigue
and systemic arterial pressure in human subjects. J Appl Physiol
86: 845-851, 1999.
34. Yamada, E, Kusaka, T, Miyamoto, K, Tanaka, S, Morita, S, Tanaka, S, Tsuji, S, Mori, S, Norimatsu, H, and Itoh, S. Vastus lateralis oxygenation and blood volume measured by near-infrared spectroscopy during whole body vibration
. Clin Physiol Funct Imaging
25: 203-208, 2005.
Keywords:© 2010 National Strength and Conditioning Association
shaking out; vibration; rock climbing; blood flow; fatigue