Poor recovery.

shaf238 wrote: »

Need more food and/or rest by the sounds of things but as posters above have already asked, it would be helpful to have a bit more information.

Yup. Sound like food/rest to me as well.

Without any information around your volume, my impression is that you've increased your training density (density = frequency*duration) based on your comment that you've "reintroduced running while progressively increasing resistance, weight and intensity". This could surely result in building fatigue.

As far as addressing it, an example might help. In the endurance sports, athletes are very focused on the cumulative fatigue that builds over weeks of training. This is known as Cumulative Training Load. To manage and shed fatigue, most (if not all?) athletes employ a plan that relies on "periodization" where recovery weeks are built in to the training schedule, say every 4th week. Recovery weeks often employ both reduced volume and reduced intensity.(Rest days) By monitoring fatigue, both acute training load (how much stress did a particular workout cause?) and cumulative training load (how much fatigue is being carried based on the last XX days of training) can be tracked to allow athletes to reach high levels of fitness over time.

Many athletes focused on a lifting program use a similar approach when they employ "de-load weeks".

Again, I don't know what type of plan you are following, so feel free to ignore if this doesn't fit your situation. But, if you are curious, you might look up a "periodization" and "supercompensation over time" to see how these approaches build fitness. Good luck!