Over the past decade, high-intensity interval training (HIIT) has captivated the attention of the scientific community and health and exercise professionals alike, largely because it has been shown to improve cardiorespiratory fitness and cardiometabolic health for a lesser weekly time commitment relative to the current aerobic physical-activity guidelines. While most research has focused on the time-efficiency of HIIT for cardiorespiratory fitness, it is equally critical that training for muscular strength/endurance, flexibility, balance and other areas of fitness are also time-efficient. With that in mind, this article highlights specific strategies you can use with your clients for creating time-efficient workouts that target the entire fitness spectrum and move beyond aerobic HIIT.

Why is Time-efficient Exercise Programming So Important?

The most widely accepted physical activity recommendations urge American adults to accumulate at least 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity aerobic physical activity per week, or a combination of the two. These recommendations are based on research demonstrating that this level of exercise provides numerous health and fitness benefits. Unfortunately, the proportion of American adults meeting these recommendations is quite low, with research suggesting adherence rates of less than 5% when measured objectively. Although the factors explaining low exercise uptake and adherence are complex, the most common reported barrier to exercising regularly is a lack of time. Clearly, offering clients time-efficient exercise opportunities is crucial for helping them meet these minimum recommendations.

The Evolution of REHIT for Cardiorespiratory Fitness

HIIT involves multiple (approximately four to 10 repetitions) brief bouts (20 seconds to five minutes) of high-intensity exercise [80 to 100% peak heart rate (HRpeak)], interspersed with either rest or low-intensity workloads throughout an exercise session. Another prominent form of interval training is known as sprint interval training (SIT), which is characterized by repeated (six to 10 bouts) 20- to 30-second all-out supramaximal sprints [greater than 100% maximal oxygen uptake (VO2max)]. This strategy enables individuals with a low level of fitness to accumulate periods of vigorous- to high-intensity exercise that would otherwise not be possible if attempted continuously.

However, one drawback to the protocols employed in most previous HIIT/SIT studies is that they are not actually time efficient. In fact, most HIIT/SIT protocols require a time commitment (approximately 120 minutes per week) that is similar to the current recommended exercise guideline of 150 minutes per week of moderate-intensity physical activity. Moreover, it has also been suggested that the potential for a negative perceptual response to high-intensity exercise heightens with increasing repetition. Thus, for HIIT or SIT to be a feasible option to improve public health, it must be made time-efficient by specifically reducing the number of bouts (intervals) performed at vigorous- to high-intensity exercise.

More recent research has shown that a modified version of SIT known as reduced-exertion high-intensity interval training (REHIT), characterized by minimal sprint durations and repetitions (2 x 20-second sprints), produces substantial cardiorespiratory fitness benefits. The premier benefits of REHIT are two-fold: (1) it optimizes the time efficiency of exercise sessions; and (2) it permits clients to perform a more manageable intensity regimen. Indeed, there is now convincing scientific evidence from ACE-supported research (see sidebar) that REHIT is superior at improving cardiorespiratory fitness when compared with currently recommended moderate-intensity continuous training. 

In 2018, our group of researchers at Western Colorado University conducted a study to determine the effectiveness of an eight-week REHIT program for improving cardiorespiratory fitness in the workplace environment. Half of the 32 participants were randomly chosen to follow an eight-week REHIT program, while the other half was performed moderate-intensity continuous training. Cardiorespiratory fitness was measured at baseline and after eight weeks. A CAROL cycle ergometer unit was used to perform REHIT sessions three to four days per week for the duration of the study.

This figure illustrates the main fitness findings, which were as follows:

1. The REHIT workouts performed on the CAROL bike were considerably more time efficient. Total weekly exercise time of traditional workouts was 150 minutes, whereas the CAROL workouts took only 41 minutes to complete. This was approximately one-quarter the time commitment of traditional workouts.   

2. The REHIT exercise group improved their fitness nearly twice as much (12.3%) as those who performed traditional, moderate-intensity workouts (6.9%)

Multi-tasking, Time-efficient Exercise Programming Strategies

Cardiorespiratory, flexibility, neuromotor and muscular training are each paramount for the overall health, physical fitness and well-being of individuals. As a health and exercise professional, you follow established industry guidelines, such as those published by the American College of Sports Medicine (ACSM), when designing training programs to positively modify each of these fitness components. However, to fulfill maximum frequency requirements and exercise guidelines for each form of activity (14 overall; five cardiorespiratory bouts, three flexibility bouts, three neuromotor bouts and three resistance bouts), it is necessary for individuals to perform at least two (or more) activities on the same day, and most likely within the same exercise session. Clearly, this approach is not time-efficient and undoubtedly presents a barrier for many of your clients.

An alternative, and likely more successful, strategy for individuals to achieve these recommended guidelines for each form of activity is for the exercise modality itself to permit simultaneous training across various fitness components (e.g., neuromotor and cardiorespiratory). In fact, previous ACE-supported research, which is described below, has demonstrated that this multitasking approach is a time-efficient strategy for simultaneously improved multiple domains of fitness.

Core-Tex Training

In this study, a cohort of 15 healthy men and women participated in a six-week exercise-training program with the Core-Tex. After six weeks, participants experienced the following improvements:

  • 8% increase in cardiorespiratory fitness
  • 2% increase in upper-body muscular fitness
  • 6% increase in lower-body muscular fitness
  • 5% increase in flexibility
  • 6% increase in balance (i.e., neuromotor)

This study demonstrated that Core-Tex improves various domains of fitness in a time-efficient manner. In fact, the findings demonstrated that the Core-Tex may simultaneously satisfy training guidelines for cardiorespiratory, flexibility, neuromotor and muscular fitness in just two hours of exercise per week.

TRX Suspension Training

Over the past decade or so, the TRX Suspension Trainer has become a mainstay in gyms and training studios around the world. Leveraging gravity and the exerciser’s body weight as resistance, it is possible to perform hundreds of exercises on the TRX Suspension Trainer, making it a favorite of health and exercise professionals. In this study, a cohort of 16 healthy men and women participated in an eight-week exercise-training program with TRX Suspension Training. After eight weeks, participants experienced the following improvements:

  • 5% increase in cardiorespiratory fitness
  • 7% increase in upper-body muscular fitness
  • 6% increase in lower-body muscular fitness
  • 6% increase in flexibility
  • 3% increase in balance (i.e., neuromotor)

This study showed that TRX Suspension Training is holistically beneficial, as evidenced by the improvements observed across all fitness domains. It’s also worth noting that these results were achieved over only eight weeks of training on three days per week. Clearly, this type of training program is an ideal multitasking, time-efficient exercise programming strategy.

Final Thoughts

As a health and exercise professional, one of the biggest obstacles you must overcome in supporting your clients’ adherence to exercise programs over the long term is a perceived lack of time. REHIT workouts are more potent and more time-efficient than traditional moderate-intensity continuous training. REHIT and other multitasking, time-efficient exercise programming strategies are a great way for you to assist your clients as they work to achieve their goals across the entire fitness spectrum.