High-intensity training: a 14-minute recipe for success?

Optimizing the time-energy equation

While we now know for sure that the benefits of adding strength training to a endurance-training program are very significant and irrefutable, why is it that many endurance athletes do not perform strength training as part of their regular training regime? There are a number of possible explanations for this. Some athletes may still be under the mistaken impression that strength training is only for athletes who want to get big and bulky. Others may lack the knowledge or confidence to get started on a strength routine. It may even simply be due a lack or cost of strength training facilities in the area. In my experience (as an ex-coach) however, the most common reasons given are the cost to the athlete in terms of time and energy.

When adding strength training to an endurance program, there is an unavoidable a trade off at play; performing high-quality strength sessions requires extra time and significant amounts of mental and physical energy. But the same requirements are also true of the athlete’s sport-specific training sessions. Because there’s only so much time and energy an athlete has before they risk becoming excessively stressed and fatigued (with all the potential impacts on sport performance that involves), many athletes feel reluctant to spend that extra time and effort strength training. And when offered the option to slightly cut endurance training volume to compensate for a little added strength training, many endurance athletes eschew this option, believing (incorrectly) that any drop in their endurance training volume will inevitably lead to poorer endurance performance – something that research has disproved^(6,7).

Combining intervals and strength

Perhaps the best way to overcome these concerns is to ensure that any strength training performed is as productive as possible for the time and energy invested. By doing this, improved muscle strength and economy (leading to better endurance performance) can be had while minimizing demands on the athlete’s physical reserves. In short, strength training should produce the biggest bang per unit of time and effort invested. One approach to maximize endurance benefits and minimize time invested is to combine high-intensity endurance training sessions such as intervals with some relevant strength training – so called concurrent training.

This concept isn’t new; the ‘traditional’ circuit training workouts aimed to do just that, improving muscular strength and cardiovascular fitness simultaneously⁽⁸⁾. The beauty of this approach is that endurance athletes who may be reluctant to spend time and effort performing a pure strength routine can take comfort from the fact that concurrent strength-endurance sessions will not just build strength (and muscle economy), but can also further develop aerobic power and endurance performance. There are numerous methods of putting together concurrent training sessions, but if you’re an endurance athlete who really wants to minimize your time investment while still developing endurance-specific strength and muscle economy, new research published by a team of Greek researchers may be just what you’re looking for!

New research

Published in the journal ‘Sports’⁽⁹⁾, this research looked at the physiological responses (heart rate, blood lactate concentration) and muscular performance during and following a high intensity interval session that integrated jumping and running exercises - using an optimized structure based on evidence from prior studies^(10,11). In particular, the researchers wanted to know if adding in dynamic leg strength exercises into a running interval program was able to help develop leg strength and power (vital for muscle economy) over and above that produced by performing high intensity running intervals alone.

Sixteen moderately trained athletes with good levels of endurance fitness (average maximum oxygen uptake [VO2max] scores of around 56mls/kg/min) were recruited for the study. Initially, familiarization sessions were performed in order to determine the optimum jump height for each athlete (ie the height that elicited the most power) and to introduce the athletes to the interval training structure that was to be used in the two subsequent sessions.

Following this familiarization process, the athletes performed two bouts of interval training on two separate occasions. These two interval sessions were similar but not quite the same; one session was an interval-only session while the other used a very similar structure but also included jump exercises. These two sessions were as follows:

·        Running intervals only - included two 6-minute sets of high-intensity running exercise as shown in figure 2. In each set, the participants had to complete 12 repetitions of running for 15 seconds at 100% of the velocity that elicited VO2max, interspersed with 15 seconds intervals of passive recovery. The recovery interval between the two sets was 2 minutes.

·        Running intervals + jumping - The integrated session included a combination of high-intensity running and jumping exercises of 2 × 6 minutes, as illustrated in figure 2. During each 6-minute set, the participants had to complete 4 consecutive rounds of 1.5 min, each including 2 x bouts of 15 seconds running at 100% of the velocity that elicited VO2max, and one 15-second bout of jumping (consisting of 9 drop jumps) from the predetermined height, all interspersed with 15 seconds of passive recovery. The drop jumping exercise was executed using two boxes of appropriate height, as shown in figure 3. The distance between the two boxes was 1 metre and a metronome was used to determine drop jump rate.

Figure 2&3: Running-only vs. running+jumping protocols

What they found

When it came to cardiovascular training stimulus, the researchers were surprised because although it containing less running intervals, the running + jumping protocol elicited a far superior heart rate response. In particular, the time spent above 85% maximum heart rate (85% HRmax – a key parameter of how much aerobic training stimulus is applied during an exercise bout) was two-fold higher in the running + jumping protocol compared to running only (8.5 vs. 4.3 minutes respectively) – see figure 5. Moreover, the time spent above 90% HRmax was more than 4-fold higher in the running + jumping protocol compared to running only (5.0 vs. 1.2 minutes respectively).

Figures 4&5: Heart rates during running-only vs. running + jumping protocol (top) & post-training countermovement jump performance (bottom)

Top: Black solid trace = running + jumping. Blue solid trace = running only. Orange dotted line indicates 85% of HRmax and red dotted line indicates 95% of HRmax.
Bottom: Black dots = running + jumping protocol; white dots = running-only protocol.

Take home lessons for athletes

In their summing up, the authors of the above paper concluded that “an integrated running/jumping high-intensity interval exercise approach could be a very useful and time efficient method for strength and conditioning coaches, especially in team sports, where the time available for the improvement of physical parameters is often limited”. However, given the very high cardiovascular stimulus produced by the insertion of a few bursts of jumps into a short session of high-intensity intervals, this approach would undoubtedly prove beneficial for endurance athletes too, especially when time is tight or for those who are reluctant to perform conventional strength training in the gym.

In addition to aerobic conditioning, this running + jumping protocol also enhanced countermovement jump performance, which shows it was effective at generating a good neuromuscular response. That matters because such a stimulus (using explosive jumping) is also associated with improvements in strength, power and muscle economy^(12-14). Therefore, if endurance athletes can gain more power, strength, muscle economy and aerobic power by carrying out some 14-minute interval running + jumping sessions, there are good reasons for trying this approach!

In practice

Despite its brief duration, the running + jumping protocol as outlined above was fairly demanding. For endurance athletes and/or coaches who want to try it therefore, this kind of session is best carried out when athletes are mentally and physically fresh. When setting up the jumping box, what height should it be. In the study above, the researchers experimented with different box heights from 30-60cms then used a simple but scientifically validated^(15-19) phone app called ‘My Jump2’, which is available on the Apple/iPhone platform. Essentially, this app calculates jump height, flight time, velocity, force and power of an athlete’s vertical jumps. Also, it gives athletes the contact time, vertical stiffness and reactive strength index (RSI) of their drop jumps. Moreover, it allows you to calculate force-velocity profile when using different jump heights. By experimenting with a range of box heights, you can find which produces the best power profile.

One word of caution however; it is advisable to closely stick with the protocol above, which was chosen carefully with a delicate balance in mind. On the one hand, there had to be enough jumps included in each burst (nine in this case) to produce an excellent aerobic stimulus. Research shows that reducing the number of jumps from nine to seven per burst significantly reduces the aerobic stimulus produced⁽²⁰⁾. On the other hand, performing too many jumps in total appears to reduce the neuromuscular response, most likely due to excessive fatigue⁽²¹⁾. This of course is undesirable in terms of muscle economy gains, so athletes shouldn’t be tempted to get carried away!

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