Impact of High-Intensity Interval Duration on Perceived Exertion
The rate of perceived exertion (RPE) has traditionally been used to monitor in-task exercise intensity. Current research indicates that anticipated, in-task, and postexercise RPE values can be notably different from each other. An important new consideration is how such perceptions are impacted by high-intensity interval training (HIIT). HIIT has been shown to have significant physiologic benefits in both fit and unfit participants. Therefore, a need exists to learn more about the perceptual aspects of interval versus continuous exercise as a means to assist in exercise prescription.
The purpose of this study, in the May 2015 issue of Medicine & Science in Sports & Exercise®, was to investigate the exertional responses before, during, and after exercise between one 20-min trial of heavy-intensity continuous (HC) exercise and three 24-min trials of severe-intensity interval exercise with varied interval durations in a mixed-gender sample of inactive, overweight, and unfit adults (2). The interval training used 1:1 work-to-recovery ratios of 30 s (SI-30), 60 s (SI-60), and 120 s (SI-120).
Subjects completed six trials, each separated by at least 48 h, and trials were completed over 2 to 4 wk. The first trial was a protocol to measure peak oxygen uptake (V˙O2peak). The second trial was used to familiarize the participants to the upcoming experimental trials. The remaining experimental trials included the one HC trial and the three interval sessions: SI-30, SI-60, and SI-120.
Continuous and interval trials differed on total duration but were equal in terms of total external work.
RPE was assessed before, during, and after exercise using the single-item CR10 scale ranging from 0 to 10. The label for 0 is “nothing at all,” and the label for 10 is “very, very hard (maximal),” with 3 representing “moderate” and 5 representing “hard.” Preexercise RPE was taken immediately after the participant was provided with a description of the upcoming trial. In-task RPE was assessed 12 times during the trials and occurred during the last 10 s of the work and recovery intervals approximating 1/6, 1/3, 1/2, 2/3, 5/6, and 6/6 of trial completion. Postexercise RPE was assessed immediately following cooldown and again 10 min later. Heart rate (HR) served as the objective measure of exercise intensity and was recorded using an HR monitor while collecting RPE data.
Results demonstrated that anticipated exertion was highest in the SI-120 trial compared with that in other trials. In-task RPE increased from beginning to end in all trials, with greatest increases within the HC trial. Session RPE for the SI-120 trial was significantly higher than that for all other trials, and the SI-30 trial was significantly lower than the HC trial. Predicted and session RPE values also were compared and revealed no differences for HC and SI-60 trials but indicated that session RPE was significantly lower than predicted RPE for the SI-30 trial and predicted RPE was significantly lower than session RPE for the SI-120 trial immediately after exercise but not 10 min after exercise.
These findings suggest that 30-s HIIT protocols limit the perceptual drift that occurs during exercise in comparison with that in heavy continuous exercise. In addition, performing more intervals with shorter durations appears to produce lower postexercise RPE values than fewer intervals of longer duration and equal intensity.
Bottom Line: Since RPE before, during, and after exercise may influence behavior, these results should provide reason to consider the prescription of shorter duration interval training in overweight sedentary adults.
Tendon Vibration Does Not Alter Recovery Time Following Fatigue
Research has demonstrated that tendon vibration can enhance muscle activity and increase muscular endurance times; however, the impact of vibration on recovery from fatigue is not known. The purpose of this study in the May 2015 edition of Medicine & Science in Sports & Exercise® was to investigate the impact of activation of Ia sensory neurons, through tendon vibration, on recovery of force and electromyography following fatigue of the ankle dorsiflexor muscles (1). Given the excitatory influence of tendon vibration on the motor neuron pool, the authors hypothesized that relative to a sham condition, recovery from fatigue would occur more quickly when vibration was applied to the tendon during the recovery period.
The study enlisted eight sedentary males to perform a fatiguing protocol of the ankle dorsiflexor muscles on two separate days, with a minimum of 72 h between each visit. Surface EMG was recorded from the tibialis anterior (TA) muscle while participants performed 25 maximal voluntary contractions (MVC), each lasting 5 s and separated by 2 s. Following the fatiguing protocol, recovery was assessed with 3-s MVC each minute over a 10-min period. Recovery was defined as the time for force to return to 90% of baseline. On one visit, vibration was applied between MVC, throughout recovery, to the distal tendon of the TA. The alternate visit involved a sham condition in which no vibration was applied.
MVC force and EMG amplitude were not significantly different across testing days. Both MVC force and EMG amplitude declined significantly at the end of the fatigue protocol. However, there were no significant interaction effects for MVC force or EMG amplitude, indicating similar levels of fatigue across days. With tendon vibration, MVC force recovered within 4.0 ± 2.5 min, which was not different than the sham condition. Similarly, EMG recovery time was not different between vibration and sham conditions.
These results suggest that activation of excitatory group Ia afferents through tendon vibration does not substantially alter recovery time following fatigue. One consideration that the authors mentioned was the fact that the study participants were healthy young males. It is possible that in a different population, such as older adults or those with diminished sensory feedback, vibration may have sped recovery.
Bottom Line: Tendon vibration does not alter recovery time following fatigue in young, healthy males.
1. Christie A, Miller NR. Tendon vibration does not alter recovery time following fatigue. Med. Sci. Sports Exerc.
2015; 47: 1038–45.
2. Kilpatrick MW, Martinez N, Little JP, et al. Impact of high-intensity interval duration on perceived exertion. Med. Sci. Sports Exerc.
2015; 47: 931–36.