Acute Passive Static Stretching and Cramp Threshold Frequency

Context: Exercise-associated muscle cramps are a common clinical problem for athletes. Objective: To determine whether acute passive static stretching altered cramp threshold frequency (CTF) of electrically induced muscle cramps. Design: Crossover study. Setting: Laboratory. Patients or Other Participants: Seventeen healthy college-aged individuals. Intervention(s): Stretching or no stretching. Main Outcome Measure(s): The independent variable was the static stretch versus the no-stretch condition, and the dependent variable was the CTF. Results: The CTF increased in both the control (pretest: 18.12 ± 6.46 Hz, posttest: 19.65 ± 7.25 Hz; P = .033) and stretching (pretest: 18.94 ± 5.96 Hz, posttest: 20.47 ± 7.12 Hz; P = .049) groups. No difference between the groups was found (t15 = 0.035, P = .97). Conclusions: Acute passive static stretching did not seem to increase the CTF.

Are electrically induced muscle cramps able to increase the cramp threshold frequency, when induced once a week?

The cramp threshold frequency (CTF) is known to be positively correlated with the individual cramp susceptibility. Here we assessed CTF changes after two bouts of electrically induced muscle cramps (EIMCs). The EIMCs (6×5 sec) were unilaterally induced twice (separated by one week) in the gastrocnemius of an intervention group (n=8), while 5 participants served as control. The CTF increased from 25.1±4.6 Hz at baseline to 31.4±9.0 Hz and 31.7±8.5 Hz 24 h after bout 1 and 2 (P<0.05). Thereafter, the CTF declined following both bouts to reach values of 28.0±6.7 Hz and 29.1±7.7 Hz after 72 h after bout 1 and 2. Creatine kinase (CK) activity and perceived discomfort during cramps was lower after bout 2 (P<0.05). CTF, CK, and discomfort did not change in CG. That is, a single bout of EIMCs induces a 24 h CTF increment and a second bout sustains this effect, while perceived discomfort and muscle damage decreases. This short term effect may help athletes to reduce the cramp susceptibility for an important match.

Initial Electrical Stimulation Frequency and Cramp Threshold Frequency and Force

Context In the electrically induced cramp model, the tibial nerve is stimulated at an initial frequency of 4 Hz with increases in 2-Hz increments until the flexor hallucis brevis cramps. The frequency at which cramping occurs (ie, threshold frequency [TF]) can vary considerably. A potential limitation is that multiple subthreshold stimulations before TF might induce fatigue, which is operationally defined as a decrease in maximal voluntary isometric contraction (MVIC) force, thereby biasing TF. Objective To determine if TF is similar when initially stimulated at 4 Hz or 14 Hz and if MVIC force is different among stimulation frequencies or over time (precramp, 1 minute postcramp, and 5 minutes postcramp). Design Crossover study. Setting Laboratory. Patients or Other Participants Twenty participants (13 males: age = 20.6 ± 2.9 years, height = 184.4 ± 5.7 cm, mass = 76.3 ± 7.1 kg; 7 females: age = 20.4 ± 3.5 years, height = 166.6 ± 6.0 cm, mass = 62.4 ± 10.0 kg) who were prone to cramps. Intervention(s) Participants performed 20 practice MVICs. After a 5-minute rest, three 2-second MVICs were recorded and averaged for the precramp measurement. Participants were stimulated at either 4 Hz or 14 Hz, and the frequency was increased in 2-Hz increments from each initial frequency until cramp. The MVIC force was reevaluated at 1 minute and 5 minutes postcramp. Main Outcome Measure(s) The TF and MVIC force. Results Initial stimulation frequency did not affect TF (4 Hz = 16.2 ± 3.8 Hz, 14 Hz = 17.1 ± 5.0 Hz; t19=1.2, P = .24). Two participants had inaccurate TFs when initially stimulated at 14 Hz; they cramped at 10 and 12 Hz in the 4-Hz condition. The MVIC force did not differ between initial frequencies (F1,19 = 0.9, P = .36) but did differ over time (F2,38 = 5.1, P = .01). Force was lower at 1 minute postcramp (25.1 ± 10.1 N) than at precramp (28.7 ± 7.8 N; P < .05) but returned to baseline at 5 minutes postcramp (26.7 ± 8.9 N; P > .05). Conclusions The preferred initial stimulation frequency might be 4 Hz because it did not alter or overestimate TF. The MVIC force was lower at 1 minute postcramp, suggesting the induced cramp rather than the varying electrical frequencies affected force. A 1- to 5-minute rest should be provided postcramp induction if multiple cramps are induced.

Duration of Electrically Induced Muscle Cramp Increased by Increasing Stimulation Frequency

Context:Electrically induced muscle cramps (EIMC) do not last long enough to study many cramp treatments. Increasing stimulation frequency lengthens cramp duration; it is unknown which frequency elicits the longest EIMC.Objective:To determine which stimulation frequency elicits the longest EIMC and whether cramp duration and stimulation frequency are correlated.Design:Randomized, crossover.Setting:Laboratory.Participants:20 participants (12 male, 8 female; age 20.7 ± 0.6 y; height 174.9 ± 1.9 cm; mass 76.6 ± 2.2 kg) with a self-reported history of muscle cramps in their lower extremities within the 6 mo before the study.Interventions:The dominant leg’s tibial nerve was percutaneously stimulated with 2-s-duration electrical stimuli trains starting at a frequency of 4 Hz. After 1 min of rest, stimulation frequency increased in 2-Hz increments until a cramp occurred in the flexor hallucis brevis. The stimulation frequency at which a cramp occurred was termed cramp threshold frequency (TF). Cramp duration was determined using strict clinical criteria (loss of hallux rigidity and return of hallux neutral). On the next 4 consecutive days, participants were stimulated at 5, 10, 15, or 20 Hz above TF, and cramp duration was reassessed.Main Outcome Measures:Cramp TF and duration.Results:Cramp TF was 16.9 ± 5.1 Hz. Cramp duration was longer at 15 and 20 Hz above TF (77.9 ± 37.6 s and 69.5 ± 36.9 s, respectively) than at TF (40.8 ± 34.0 s; P < .05). Cramp duration and TF were highly correlated (r = .90). Conclusions: Stimulating at 15 and 20 Hz above cramp TF produces the longest-lasting EIMC.