The prevailing training advice to \u2018keep your hard days hard and your easy days easy\u2019 is intended to be simple \u2013 but in reality, it can really mess with your head. Most runners understand what \u2018easy\u2019 feels like (although whether they have the restraint to stick to that pace is another story). But \u2018hard\u2019 is entirely different territory. Just how hard should \u2018hard\u2019 actually be? How do you measure it? Is it possible to run a hard run too hard?<\/p>\n
To get some perspective, we chatted with a handful of experts about the appropriate intensity for hard runs, signs that you might be overdoing it and all the benefits that you get from pushing the needle.<\/p>\n
How hard should a hard run really feel?<\/p>\n
One of the issues with the concept of a \u2018hard run\u2019 is that it\u2019s subjective. A sprinter may find a three-mile jog challenging, while a distance runner would rather run 10 miles at a steady pace than crank out a handful of track intervals<\/a>. Then, of course, there are all the factors that can make runs harder than initially intended, like weather, terrain, gastrointestinal issues and how well you slept the night before.<\/p>\n Individual runners\u2019 circumstances and preferences aside, when coaches talk about running hard, they\u2019re usually referring to speed and intensity. A hard run is some kind of structured, faster training session, Jason Fitzgerald, USATF-certified coach and the host of the Strength Running Podcast<\/a>, tells Runner\u2019s World, which means that it\u2019s faster than the foundational miles that you log at a conversational pace<\/a>.<\/p>\n Just how fast you run on a hard day depends on the intended purpose of that workout, as different levels of intensity elicit different training adaptations. Essentially, it\u2019s about choosing the appropriate tool for the task at hand.<\/p>\n The \u2018hard run\u2019 falls on a spectrum. For example, you might run a 5K<\/a> at a hard, race pace effort of 7:30 min\/mile. However, Fitzgerald explains, a lactate threshold<\/a> training run, while still \u2018hard\u2019, is typically 30 to 45 seconds slower per mile than your 5K race pace. So, you would likely run a lactate threshold run at a pace of 8:00 min\/mile. And if your workout calls for you to run intervals at your one-mile<\/a> race pace, you\u2019d want to push yourself to run at a pace of around 7:00 min\/mile, or 30 seconds faster than your 5K pace.<\/p>\n All of these runs are \u2018hard\u2019, but they\u2019re specific to the distance and the purpose of the workout.<\/p>\n What metrics should you monitor during your hard runs?<\/p>\n Intention is key when it comes to hard runs, says Kaleigh Ray<\/a>, certified running coach and exercise physiologist. \u2018The purpose of the hard run should be to develop something specific and this is something that runners should be able to articulate before they do their hard run,\u2019 she says. <\/p>\n This is where working with an experienced coach or following a thoughtfully designed training plan<\/a> can be helpful. That way, you\u2019re not just winging it or pushing yourself for the sake of doing a tough workout.<\/p>\n Applying metrics to your run can also help to ensure that you\u2019re staying on track and in line with your original intention. \u2018It can keep runners at the right intensity without doing too much and overloading or doing too little and not getting the stimulus that they\u2019re looking for,\u2019 says Ray.<\/p>\n Fitzgerald is a proponent of using race history to set the pace for hard runs and often encourages beginner runners to register for a few short races after a couple of months of training. \u2018That provides a baseline for understanding where their fitness is at,\u2019 he says. \u2018If you have a substantial race history, you\u2019re going to know your mile race pace, your two-mile race pace, your 5K race pace \u2013 and you\u2019re going to be able to execute workouts [that align with those paces] more effectively,\u2019 he says.<\/p>\n If you don\u2019t have recent race data, you can also keep an eye on your heart rate<\/a>. \u2018If you\u2019re looking at a five [heart rate] zone training model, I would say that a hard run is zone 4 or 5, whereas zones 1 and 2 are easy and zone 3 is like a tempo [or moderate intensity],\u2019 says Todd Buckingham, Ph.D. exercise physiologist at PTSportsPRO<\/a> in Michigan.<\/p>\n To determine your heart rate zones, first estimate your maximum heart rate (MHR). (Subtracting your age from 220 is one easy method, but there are other equations that may be more precise.) Each heart rate zone is a percentage of your estimated maximum heart rate:<\/p>\n Zone 1: less than 57% of MHRZone 2: 57-63% of MHRZone 3: 64-76% of MHRZone 4: 77-95% of MHRZone 5: greater than 95% of MHR<\/p>\n Alternatively, you can use your own rate of perceived exertion (RPE)<\/a>, which you use to subjectively grade your effort on a scale of one to 10, where one is resting and 10 is a maximal, all-out effort.<\/p>\n Will Baldwin<\/a>, USATF and VDOT-certified running coach, considers any run that\u2019s at an RPE of seven or higher to be hard. He also notes that you don\u2019t need to maintain a hard pace for the duration of a workout for it to be considered hard. \u2018We\u2019ll usually have an easy warm-up, some strides<\/a> and a few different pace ranges,\u2019 he says. \u2018It\u2019s usually segmented and broken up into smaller chunks, including rest intervals. We\u2019ll almost never have a run that\u2019s all hard.\u2019<\/p>\n How can you benefit from running hard?<\/p>\n Besides adding variety to your training and boosting your confidence, hard runs offer some unique training benefits. Among the most important physiological adaptations is improved lactate threshold<\/a>, which refers to the body\u2019s ability to clear lactate \u2013 a metabolic byproduct \u2013 from the blood and use it for energy.<\/p>\n When you train at your lactate threshold pace or faster, your ability to buffer lactate, particularly in zone 4 (the threshold zone), is going to improve, says Buckingham. This means that you can run harder for longer without fatiguing.<\/p>\n High-intensity exercise, like running hard, also affects mitochondria, which are located in the body\u2019s cells and convert oxygen to adenosine triphosphate (ATP), the body\u2019s energy currency. A recent study<\/a> compared the effects of moderate-intensity exercise and those of high-intensity exercise on mitochondria (often referred to as the \u2018powerhouse\u2019 of the cell) in 20 healthy subjects. After six weeks of training, both groups saw improvements in mitochondrial content and overall fitness. However, high-intensity exercise appeared to be more effective at driving mitochondrial adaptations \u2013 and more\/bigger mitochondria means more available energy.<\/p>\n Lots of research also shows that high-intensity interval training (definitely considered a hard run), can help to boost your VO2 max<\/a>, or the measurement of maximum oxygen intake and use during cardio exercise. For example, one meta-analysis<\/a> found that just four weeks of HIIT workouts, with 30-second intervals and about five minutes of volume, increased VO2 max. And increasing the duration of training, the length of the intervals and the total volume led to even greater effects.<\/p>\n Running fast will also develop muscular power, which you need to charge up a hill or sprint across the finish line. And while it may seem obvious, you have to practice running fast to be able to run fast. \u2018The faster you run, the more of an athletic movement it is,\u2019 says Fitzgerald. Hard runs, he explains, will improve your turnover and your coordination.<\/p>\n How do you know if you\u2019re running too hard?<\/p>\n Each type of hard run demands a specific level of speed and intensity, but it is possible to run too hard, no matter what kind of workout you\u2019re doing. Here are three obvious signs that you need to take things down a notch.<\/p>\n 1. Your form breaks down<\/p>\n If picking up the pace is wrecking your posture, messing with your gait or creating movement inefficiencies (think: flailing arms), it\u2019s not worth it.<\/p>\n